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Hey Guys.  I have enclosed a link to the noise this engine has.  I have not been able to figure this one out.  Here's a little history and the diagnostic procedures used so far.

https://www.youtube.com/watch?v=Oa12bVGEOwU&feature=youtu.be

This engine is a "refresh".  It's in a 98 TJ that blew its engine.  I pulled this engine from a pull-n-pay out of a Dakota.  When I tore it down it was clear the chain tensioner had destroyed itself and gone through a couple bearings.  I did a complete refresh on the Dakota engine.   Took it down to the block and thoroughly cleaned it with electrolysis, warm solvent soak, pressure wash, soap and water cleanup of all passages. Cam bearings, dingle hone cylinders, all new bearings throughout, new rings-properly clocked, new lifters, new pushrods, Cleaned and lapped the heads (valves). New intake and exhaust valves on #4 cylinder.  New oil pump.  The old cam and crank were fine so I used them.

The engine runs great and has good "pop" for a 4-banger.  It runs smooth with no misses.  I broke it in and drove it around a bit so the computer could relearn the fuel trims and to get some back-pressure on the rings with some semi-hard slow pulls.

The noise is deep in the block and toward the rear.  Specifically it seems to be mid-block and around the #3 or #4 cylinder.  The noise is its worst at idle.  With even a slight throttle change it disappears.  It doesn't knock at anything but idle.  I cut-out (killed) each cylinder and it did not change the sound.  I really suspected a lifter was not charging.  Indicators were the location of the noise and the fact that it went away with 'any' acceleration (thus charging the lifter with a touch more oil pressure).  I suspected a weak lifter and ruled-out everything else, so I replaced the lifters.  Same sound.  I took the pan off.  No metal in the pan.  Pulled the break-in filter apart.  No metal in the filter.  It has 40 psi consistently at idle (rises with acceleration).  (10W30) With the pan off, I checked each rod on all four quadrants=no movement.  I pulled the caps off #3 and #4 rods and the bearings are perfect.  I suspected piston slap.  Moved the pistons through their range, examining each.  At the top of the stroke (rotating the engine back and forth) I watched the piston skirts for movement [because the force axis on the piston changes].  There was no lateral movement.  The #4 piston had "maybe" a 16th of an inch lateral movement at the bottom of the skirt.  (It was barely perceptible).  I don't believe this is enough to cause piston slap.  The engine has no noise upon startup, and begins this knocking after about 30 seconds usually.  It doesn't seem to change with engine temperature.  I went back to the top of the engine and pulled the valve cover.  All the rockers were tight.  I ran the engine and pressed down on each valve.  There was no "clacking" or any indication there was any play in any valve.  I can take/post more videos if it would be helpful.

I think that about covers it.  Hopefully I've included all the variables.  I'm out of ideas!  Any help would be much appreciated!  Thank-you!

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I value your thoroughness and detailed description of the work performed, Wayne.  You're taking a conscientious and professional approach.  Here are two suggestions:

1)  You may have a lean, individual cylinder knock at idle.  An injector pulse tool like the Waekon 76462 could indicate an injector that is "misfiring" or, better yet, an inexpensive diagnostic tool for injectors could test the actual flow behavior: 

https://www.amazon.com/Waekon-76462-Universal-Electronic-Injector/dp/B0021V0FRE/ref=sr_1_12?dchild=1&keywords=fuel+injector+pulse+tester&qid=1607533364&s=automotive&sr=1-12

or 

https://www.amazon.com/Professional-Injector-Kawish-Automotive-Diagnostic/dp/B07V43G3H3/ref=psdc_15727741_t1_B0021V0FRE  [This is just one example at Amazon, there may be other devices that you will prefer, including OTC.  Each is relatively inexpensive in this tool class.]

2)  The noise is in the area of the distributor and oil pump.  Use a stethoscope, sounding rod or, ideally, a Steelman Chassis/Engine EAR tester to see whether the distributor shaft or drive gear, or even the new oil pump, is creating a knocking noise.  I have a Chassis/EAR that does wonders with its multi-channel sound comparisons:

https://www.amazon.com/Steelman-06606-ChassisEAR-EngineEAR-Combination/dp/B001G1JKPS/ref=sr_1_4?dchild=1&keywords=steelman+sound+tester&qid=1607533946&s=automotive&sr=1-4

The Steelman tool is also useful for comparing and contrasting the origins of a knocking sound, separating the six channels will indicate the intensity and decibel contrast.

Despite your fuel trim checks, there may be a specific injector(s) getting a very lean idle mix and creating knock.  As you hint, knock or ping is piston rock.  If your calculation is right about piston skirt clearance, and you've ruled out "slap", this may simply be a cylinder/piston knock from a lean idle mixture.  Also use a timing light to see how much advance you have at idle, significant advance can contribute to knock if you're running low octane fuel.  These engines do not use a knock sensor to retard timing and stop pre-ignition/knock.  Sometimes, a simple change in octane will stop knock, though the fuel price may not be desired.

I'm going to spend 2021 sharing in-depth diagnostics and troubleshooting at the magazine site.  There are lab scope procedures for associating noises with injector firing and also in-cylinder transducer pressure tests that indicate cylinder imbalance and low compression while cranking.  These techniques will help demystify electronic fuel-and-spark issues and basic engine conditions like lower compression in a given cylinder.  Two- and four-channel lab scopes move well beyond most scan tools for diagnostics.

Here is a current video series I did on engine knock analysis and injector cleaning to resolve knock caused by poor injector firing.  This could be helpful to your current issue and illustrates the use of the Steelman Chassis/EAR:

1) https://www.4wdmechanix.com/how-to-diagnose-an-engine-noise-or-knock/

2) https://www.4wdmechanix.com/curing-an-engine-knock-with-surr-tools-and-sea-foam/

This is a place to start.  Let us know what you find.  If necessary, we can go from there.

Moses

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  • Moses Ludel changed the title to Jeep TJ Wrangler Refreshed 2.5L Engine Has Knocking Noise

Hello Sir.

 

Thanks for responding.  You have certainly given me some alternate direction.  I will try to get out to the shop within the next day or two and will let you know what I find.

 

I have used a stethoscope on this engine quite a bit, but I'll keep at it.

 

Thanks again!

 

Wayne

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Wayne...I have one additional focus area to suggest.  Had the Dakota engine been previously rebuilt?  You lapped the valves and did not resurface the head or block deck.  Did you use the original pushrods when determining pushrod length?  Pushrod length is crucial on these engines, and you can check the needed pushrod length (per valve) with an inexpensive CompCams gauge for the 2.5L engine's length range. 

We have discussed correct length pushrods at the forums.  4.2L, 4.0L and 2.5L AMC engines require measuring and choosing the right length pushrods.  These topics will cast light: 

1)  https://forums.4wdmechanix.com/topic/1168-new-lifters-and-valvetrain-noise/?tab=comments#comment-8187

2)  https://forums.4wdmechanix.com/topic/1155-42l-re-build-77-cj-7-project/?tab=comments#comment-8020  [This exchange includes photos and guidelines for the CompCams gauge test of lifter length.]

Especially with a used camshaft and new head gasket, I would check the pushrod lengths.  This can be done with the cylinder head in place.  Pushrod access is with the valve cover removed.  Review our discussions on pushrod length and tests.  You may need different length pushrods at one, some or all valves.

A further comment on fuel knock...Our 4.0L '99 inline six had a knock at idle.  When I cleaned the injectors via the fuel rail (see the link in previous reply), the noise disappeared.  This suggested a lean condition on a given cylinder(s) at an idle. 

These AMC/Jeep engines set spark timing and fuel flow to a preset determined by the sensor signals and PCM programming.  One example is the oxygen sensor that looks at the exhaust stream for its combined, all cylinders oxygen content, not the O2 reading for individual cylinders.  Likewise, spark timing is fixed by sensor feedback and PCM programming.  Timing is not per cylinder advance but rather a preset number of degrees for all cylinders determined by the engine mode and operating conditions.

No two cylinders of any production engine have precisely the same timing advance needs.  The best ignition designs work in concert with a knock sensor.  They set spark advance individually for each cylinder.  In the early nineties, I played with SafeGuard ignition control by J&S Electronics (http://www.jandssafeguard.com/).  These devices can retard timing per cylinder until a knock disappears in the culprit cylinder(s).  The remaining cylinders each run at their peak tolerable advance, which is synonymous with peak power.

With SafeGuard, you can set a fixed conventional distributor to a slightly exaggerated base timing advance.  SafeGuard pulls per cylinder timing down to a knock-free level in nanoseconds.  You never hear ping from detonation.  Each cylinder runs at its individual peak timing advance—just below the cylinder's knock point.  This process is continuous, adjusting under all engine speeds and load conditions.

Without a device like the SafeGuard or a factory ignition system capable of sensing knock in individual cylinders and retarding just the culprit cylinder(s), an engine may depend upon higher octane fuel to stop knocking.  The Mopar EFI Conversion for 4.2L engines specified the use of 91-92 octane gasoline.  The MPI conversion was stock 1995 YJ Wrangler inline 4.0L six design, which has a cylinder head (combustion chambers) that is less vulnerable to knock.  The Mopar MPI used from 1991-up on 2.5L and 4.0L engines does not require a knock sensor because the combustion process is less prone to pre-ignition.

Food for thought...I would take a cranking compression test to see whether compression is high in one or more cylinders.  (This could cause knock.)  For overall condition, I use a leak down test to confirm cylinder seal.

Moses

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Oops.  I left a lengthy message a couple days ago but I don't believe I was logged-in.

I ordered the comp cams pushrod length checker:

https://www.amazon.com/gp/product/B00062YER2/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I had a bad computer day when I posted this response previously.  I also had this tool in que and did not finalize the order so it will be a bit delayed.

I checked the secondary ignition with a PICO scope.  The secondary looked good with no misfires or lean cylinders.  I listened to each injector with a stethoscope and the pintles all sounded ok.  After these checks I leaned away from a lean cylinder so I didn't scope the injectors.

However...I think you may be on to something with the pushrods.  Given the variables you described, it makes sense.  I also replaced both intake and exhaust valve in cylinder #4 with new units.  I did not measure the length of the new valves prior to installation.  While waiting for the comp cams length checker, I was considering this approach.

From another source:  "...install the bridge, pivots, rockers, and cap screws over the push rods. [with the valves closed] Slowly turn each push rod while slowly turning down the cap screws until resistance is felt in the push rod turning.

Mark the cap screw with index marks as shown in the pic. Alternate tightening the cap screws until they bottom out, then torque them to 21 ft/lbs. Observe the index mark position. This will show you the preload on the lifters."

906404419_jpgPreloadDegreesTurn.thumb.jpg.e848bce3a6a8aa3685ad8e96e9540174.jpg

 

This is a method used by crane cams.  Do you have any opinions on this method?

 

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Hi, Wayne...Yep, valve stem lengths and face margins vary, although most replacement parts are equivalent to OEM/stock.  Valve seat recession occurs, and this increases preload.  A valve may originally have a borderline pushrod length that becomes unacceptable with valve seat recession.  Lapping valves (properly) should make little preload difference, you're not removing much material at all.

The capscrew degree of rotation method relies upon several factors:  1) thread pitch on the capscrews determines the amount of drop or preload, 2) the rocker arm ratio is a factor, since the capscrew is pulling down the entire rocker arm, and 3) torque is relative to whether the threads in the head casting or capscrew have any stretch.  It's certainly a ball-park quick check.  Make sure they are talking about stock rockers or the same rocker arm ratio you're using.

When you get the gauge, you'll smile big.  It will completely demystify pushrod length.  The only measurement concern is the actual length of the pushrods, although ordering new ones to fit should be precise.  Melling offers pushrods by length.  I listed part numbers for earlier (1990-back) 4.2L engines at the '77 Jeep CJ project link.  There are many length options, see the Melling full catalog.  You'll pick a pushrod(s) that bring the valve/lifter into an acceptable range:

 

I did this vlog some time ago to provide a framework for understanding valve stem length, valve seat depth and lifter preload concerns:

https://www.4wdmechanix.com/jeep-232-258-and-4-0l-inline-six-and-2-5l-straight-four-valve-clearances-and-adjustment/

Moses

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Sorry for the delay...holidays.  I hope your Christmas went well!

I received the pushrod length checker.  I used the EOIC method to make sure I was on the base and it worked well.  I was able to obtain precise, repeatable measurements.  Each pushrod (with minor variances in a couple) measured right at 9.400.  That is zero-lash (no preload).  The pushrods I have are Melling and each measure 9.481.  Easy math...this gives .081 preload.

My initial thought was, "Perfect.  This is very high and I found my problem".  However, it is my understanding too much preload would likely cause valves to be held open.  Since my running ignition secondary patterns were good, I don't believe this to be the case.  So in a nutshell, I am not seeing any symptoms indicating this extra preload is causing issues.  I do not know how much travel the lifter plunger has total, so I'm not sure how close I am to its limits.

On another note, a compression check showed 145 psi at #1,2,4 and 125 at #3.  (5300' Elevation)  It should be noted this was not a 'proper' compression check (the engine was cold) but it gave me a reference point for relativity between the cylinders.  If this is unrelated I will look into it later.  For now, I am focusing on the knocking noise.

What do you think about that preload?  Thanks!!

Wayne

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Hi, Wayne...I like a preload of 0.030" to 0.040" in a freshly rebuilt engine.  This allows for normal valvetrain wear and moderate valve and valve seat recession over time.  The lifter preload will increase accordingly, usually just a nominal amount, before rebuilding time.  If you were using the pushrod checker during a fresh build and trying to determine the correct pushrods to order, you would order 9.440" (or closest to that length) pushrods. 

Since the camshaft is also presumed original, there's no reason to suspect that the camshaft's heel is on a greater than stock radius.  If the valve stem lengths, head gasket thickness and valve seat depths are okay, the only other variable would be the head deck height.  Uniform pushrod length measurements are a good sign.  

The 0.080" preload hints that the 2.5L may have  been cylinder head decked at some point.  I'm doubting the block deck has been milled, as you did not mention oversized pistons or other signs of a previous rebuild/remanufacturing of the engine.  A valve grind with decking is possible or an exchange/rebuilt cylinder head.  The lifter plunger travel may compensate for 0.080" preload; however, if lifter plunger/preload becomes excessive, as you note, the valves will not seat. 

For a reference, if you have any of the old 2.5L lifters, drain one of oil, reassemble it, allow the plunger to extend to the circlip, then measure how much travel you have between the plunger at the top/against the circlip and the point where the plunger stops or bottoms.  Subtract 0.080" from that measurement.  The difference is the travel range left with your current lifter preload.  You don't want too little preload, and you don't want the plunger to either block the flow of oil or bottom in the lifter body.  The plunger should "float" in the correct zone.

In the lifter, the oil acts as a solid column to support the plunger at the right height or position.  Normal oil bleed down is approximately 0.004" per crankshaft revolution, and a constant flow of pressurized oil restores the plunger height each time the valve opening and closing event takes place.  To do this, a steady and sufficient flow of pressurized oil to the lifter is essential.

Lack of oil to a lifter(s) creates clearance at the rocker arm.  While the knock is occurring, with the engine idling, check for rocker arm to valve stem clearance.  Use a feeler gauge(s).  If there is noticeable clearance, a lifter is bleeding down from either lack of oil supply or a defective lifter check ball.

Lifters can also be tested for bleed down.  Bleed down is a sign of a bad lifter (highly unlikely with new lifters) or too little pressurized oil flow through the lifter(s).  Lifter leakdown can be caused by inadequate or erratic oil flow through the lifters.  If you suspect this is the cause of your knock, check for rocker arm clearance with the engine idling and noisy.

As for the compression check, I'm not a big fan of cranking compression tests.  However, since they can be a ballpark or quick check, I would now move to a cylinder leakdown test on #3 cylinder, then the others if necessary.  A leak down test is done with the piston at TDC on the compression stroke, so the piston and rings are at the maximum wear point in the cylinder.  (This is the maximum taper point on a worn wall.  I also check pushrod length in this position, as the piston being at TDC on the compression stroke assures the camshaft heel position.  Your method should be okay, too, I used it for many years on routine valve adjustments with stock profile camshafts.)  There are "leak down" or "leakdown" discussions here at the forums, use these two key words.  You can find an inexpensive tester for $30 to $60.  It will become a handy diagnostic tool if you do this kind of work.  A quick search turned up this $25 bargain close-out at Harbor Freight.  OTC makes a kit for $75.  Depends upon how often you want to use it and the degree of accuracy demanded:

https://www.harborfreight.com/cylinder-leak-down-tester-62595.html

I went back through your initial info.  You mention piston skirt movement of 'maybe 1/16"'.  If this is anywhere near accurate, the skirt of the piston would have way too much clearance.  It's hard to gauge rock.  I would measure actual skirt-to-wall clearance with a flat feeler gauge, using care to not get the gauge stuck between the skirt and wall.   Normal lower skirt-to-wall clearance should be 0.0013" to 0.0021" for new pistons in a properly sized bore.  You suggest maybe 0.0625"?  That would be excessive.  0.003"-0.004" might be okay on a lightly honed cylinder with a good piston—a piston with proper shape and dimensionally correct.  For reference, production pistons are cam ground and not "round".  They are slightly narrower at the pin bosses, allowing for thermal expansion in this area...The skirt measurement is the reference needed.  Use the feeler at the centerline of the skirt.

I have no desire to create extra work for anyone, but if you're right about the amount of piston skirt clearance, that needs attention.  Piston skirts "shrink" from overheat and wear.  Excess wear or galling would have been noticeable.  The easiest way to measure skirt clearance in an assembled engine is to bring the piston/skirt downward to the lower end of the cylinder bore.  Stop the skirt at or slightly below the bore.  Gently work the feeler gauge between the skirt and cylinder bore/wall.  At the thickness we're discussing, any blade of 0.004" or less thickness should readily curve to the radius of the cylinder wall.  There should be virtually no bore wear at the bottom of the cylinder, so excess clearance would be due to a worn or collapsing/collapsed piston.

The other possibility is oiling, though this should not differ widely when the engine warms.  Oiling depends upon cam bearing and rod bearing oil hole alignment and clearances.  If you installed the bearings with oil holes aligned, and if the rods/pistons are in their original order and facing correctly, there should be good oil flow at the camshaft, lifters and each connecting rod squirt hole. 

You mention cam bearings.  Did you install new cam bearings or have them installed?  Were cam bearing oil holes aligned with the block passageways?  This is a long shot, but misaligned or spun cam bearings create a range of oiling issues.  When you cleaned passages, did you inspect the cam bearing oil hole alignment?

You shared that checking the new rod bearings for shake in multiple positions of the journal showed no movement.  If rods are facing correctly and in their original positions, there should be no variables created by your work.  I do use Plastigage to check the clearance at 90-degree intervals; this provides a fairly good take on the journal's roundness and the bearing oil clearance.  Jeep® oil pressure is always high, which masks irregular clearances and oil bleed-off from the sides of the rod bearings.

Check the cheeks of the rod journals for wear.  Check the rod side clearance.  Oil will bleed off the bearing(s) if there are irregularities here.  If the crankshaft has never been reground, Plastigage will enable you to make a judgment call about use of undersize 0.001", 0.002" or even 0.003" (sometimes mixtures of these undersize shell sizes, which I can discuss) on a round, slightly worn or undersize crankshaft journal.  If you determine this need, we can discuss how to size rod (or even main) bearings for the precise oil clearances you want.

Ford 300 cubic inch inline sixes were notorious for excessive rod bearing/oil clearances when new.  I dealt with that years ago and know the official Ford warranty "fix".  On that note, when rebuilding an engine with round OEM/standard size journals, polishing the journals is acceptable if the bearings are sized and fitted for proper oil clearance.  Measurements can be done on the bench with outside and inside micrometers.  If the engine is assembled or in the chassis like in your situation, sizing can be determined or confirmed with the proper use of Plastigage.

Though dropping the pan is not much fun, measuring the piston skirts might be in order.  There is some discussion of broken pistons and skirts on late nineties and early 2000s 4.0L and 2.5L Jeep engines at other forums.  A good friend with a Jeep repair shop has described broken pistons and skirts on later AMC-design Jeep engines that have accrued mileage.  While there may not be a widespread problem here, it's worth noting that piston skirts do break on these engines.  Piston slap could logically occur as well.

My takeaway from these failed piston concerns would be replacement of the OEM pistons if the engine is torn down, whether re-boring or not.  If bores are true and can clean up with glaze breaking like you performed, the same size pistons and rings should be used.  Checking ring end gaps is sensible, though nearly all service/OEM replacement ring sets are accurately pre-gapped unless noted otherwise.  High performance rings, however, usually do require gapping with a hand or power gapper.  When performing a light overhaul as you did, ring end gaps should be checked at maximum cylinder taper point in the cylinder (just below the ridge) to confirm round and degree of cylinder/bore wear.

For decades, I have used hypereutectic United Engine "Silv-O-Lite" pistons on stock engines.  Keith Black (KB) pistons are an option.  Mahle is now making Jeep® replacement pistons.  Any of these pistons would be a far better bet than the OEM.  (As you have seen, the OEM pistons have very light skirts.)  I only use forged pistons in a high compression or race engine, they are built with clearance for expansion and can be noisy when cold.

On another note, I am very interested in your use of a PICO.  I am devoting magazine how-to videos to scanners and lab scopes this coming year after attending some very interesting trade-level webinars on advanced use of these diagnostic tools.  You mention stopping short of using the tool for injector testing.  Would it warrant doing an injector test or checking fuel trim per cylinder?  This would be a basic requirement if the injectors are not flowing fuel properly or are simply "dirty".  You did do cylinder shorting to no avail, so I understand why you ruled out a lean mix knock or detonation.  My concern is that the PCM and oxygen sensor can only generalize when adjusting A/F at idle.  The result is an average rather than actual A/F per cylinder—some cylinders may be lean while others enrichen. 

Moses

 

 

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Hello Sir:

Thanks again for all the input.  That's quite a comprehensive analysis.  I have been working on another couple Jeeps with more pressing time constraints so this is a bit delayed.  I thought I'd update on some progress.  I pulled a lifter out and measured hydraulic piston travel (plunger).  For the lifters I installed, they have .198 total travel.  My preload (although high) looks like it is within the range the lifter can handle.  From here, I will likely get the Jeep back on a lift, drop the pan, and check for piston slap again.  What you've said makes sense and gives me a more accurate way to check.  If it looks good, I will re-assemble the top side (valve cover, etc.) and run the PICO tests you've described.  If the piston is indeed is the issue, I will pull the head and examine the bore for piston fit (I recently obtained a dial bore gauge).  I will definitely stay tuned and am looking forward to your videos on the PICO!

Thanks,

Wayne

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Hi, Wayne...When you pushed the lifter plunger down, did the plunger's base still clear the oil feed hole in the lifter?  The lifter needs a steady, unrestricted oil flow.  Confirm that the plunger does not block or restrict the oil feed at a preload height of 0.080".  (It shouldn't block the hole anywhere within the plunger's range of travel, but I would confirm this.)  If all looks good, normal wear over time (valve seat recession and valve face wear, primarily) should not create more than 0.005"-0.007" additional preload.

In the article section of the URL below, check out the illustrations of the two lifter cutaway views.  The plunger should be able to bottom without restricting the oil flow.  If the lifter plunger's base is floating 0.118" above this point, you should be okay:

https://www.4wdmechanix.com/jeep-232-258-and-4-0l-inline-six-and-2-5l-straight-four-valve-clearances-and-adjustment/

Note: If the noise was a lifter bleeding down from low oil at idle, there would be measurable rocker arm-to-valve stem clearance.

Your check for piston skirt to cylinder wall clearance sounds on track...Let us know what you discover.

Moses

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  • 2 weeks later...

Hello Sir:

I was able to get back to this Jeep.  I dropped the pan and followed the advice you gave.  I found the #4 piston-to-bore clearance to be .004.  I decided to check for wrist-pin movement also, and found none.  I attached a video.  The video shows me rocking the piston from side to side.  It takes a decent amount of force, but I was able to get it to "knock".  I believe this is where my problem is.  I tried to video the movement but visually it is imperceptible.  However, it can certainly be heard.  I decided a relative comparison would be in order.  I tried to get the rest of the pistons to "knock" using this method. #1 and #2 were rock solid--no movement or sound at all.  #3 had slight movement. #4 is in the video.  #4 clearance was .004".  #3 clearance was .002".

Based on this data, I was planning on removing the #4 piston and obtaining measurements of that piston and the bore.  I would make comprehensive measurements to include "out of round" and taper measurements.  This will give me some precision to work with.  

 

 

https://youtu.be/MQjSokXCvGE

Thanks again!

Wayne

 

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Wayne, this is very useful video, thanks!  Others can see what you're up against.  An audible knock at this level, especially when you rock the wrist pin, is telling.  Good job!

Very pleased that you'll take accurate measurements to determine whether this is a block/bore issue, piston wear or both.  You'll also know whether the piston has "collapsed", most often from overheating.

No ready signs of cylinder wall or lower piston skirt scuffing/drag?  The bores were smooth before you did the glaze breaking?  My bet is an overheated/shrinking or worn piston, as there is normally the slightest perceptible rock with the piston this far down in the cylinder and the factory acceptable (0.0013" to 0.0021") skirt to wall clearance.  Glaze breaking seldom removes enough material to create this degree of skirt clearance.  The problem likely existed before your initial tear down. 

Before you pull this rod/piston out of the block, with the cylinder head removed, run the piston down 3/4-inch or so in its bore to drop the piston crown just below the maximum taper point in the cylinder.  Measure your piston-to-wall (side-to-side) clearance with the piston in this position.  It will be 0.006" or more.

Moses

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Hello Sir:

I included a photo of the cylinder currently.  You can see where some scuffing is going to happen.  There is nothing that can be felt (yet), but with a good light you can see some scuffing that will develop.  I also included a photo of the bore and piston measurements.  As expected, there is too much clearance (listed).  You are correct!  Over .006" toward the top of the cylinder.

For reference, the measurements were taken just below the top ring wear, 2 5/16" down the bore (per service manual), and at the bottom wear pattern.  The piston measurements were directly beneath the rings, centerline with the wrist pin, and at the base of the piston (not at the end of the tabs, but where they 'meet' the piston 2 5/16" from the top).  In looking back at my measurements, it seems a more accurate "clearance" measurement would be the "M"iddle bore measurement against the "B"ase measurement of the piston.  I used 2 5/16" as the 'M' measurement for the bore.  The 'B' piston measurement is also 2 5/16" down the bore.  If I use this apples to apples measurement I would need to add .0002" to my 'M' clearance making it .0039.  Hopefully that makes sense.

Based on my measurements, it looks like a "C" piston would be the best fit per the service manual.  However, for this engine I was planning on using a set of Enginetech #P3071 pistons.  I'm hoping those will provide proper clearances.  I'd rather not go to a dealership for the fitted pistons ($$$).  My plan is to replace all four as a set. 

Luckily, it appears the bore is well within spec for out of round, taper, and bore size.  I will pull the rest of the pistons, measure the bores, order the new pistons (and a new head gasket), measure them prior to installation to verify fit, install them, and see how we do.

Thanks again for all of your help!

Wayne

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4.jpg

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Well.  I measured all my bores.  Some specs were slightly out. I re-measured cylinder #4 since I had a new "set-up"; for consistency.  It measured the same so that made me feel good about the accuracy/repeatability of measurements.  For reference I set my bore gauge at 3.9000" and subtracted from there.  (i.e. 3.9000 minus .0234 equals 3.8766 etc.)  I'm using a Shars 303-4737 for reference.

I also found some conflicting info in the Service Manual vs Mopar Performance Parts'  "Jeep Engines".  Nothing major, but minor differences.  (I attached a page).  Specifically the depth of measurement for pistons and a new classification for coated pistons.  These variations shouldn't affect what I found.

Also, I added a measurement labelled "D" for "deep".  I found a page specifying 3/8" from top, and 3/8" from bottom after finishing my measurements.  As mentioned, I measured the top and bottom of the ring-wear-pattern.  Next time I'll follow the manual more closely.  For these measurements, I added the bottom measurement, however, I did not re-do the top at 3/8 from the deck.  I used the top of the ring wear pattern.  If this will invalidate my measurements, I will redo that measurement.

I'm a bit concerned about cylinde r#1. .0013" out of round at the middle measurement.  If I use my new measurement at the base on the bore, my taper also rises to .0014.  Also cyl #2 .001" taper in both axes, and cyl# 3 Y-taper at .0011".  I think it will be okay since these are right at max-spec with #1 OOR being .0003 over max-spec.  I find it curious the #4 cylinder had the slap, but appears to be in the best condition as far as measurements go.  Interesting....

It has been a learning experience!

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I like your approach and thoroughness, Wayne, the bore gauge is excellent...The Jeep® Engines book was very useful, largely a compilation from the OEM factory service manuals and supplemented with racing experience.  Larry Shepard at Mopar® played a large role in that book, which was released in the era of my original Jeep® Owner's Bible™, which also carried a Mopar® Performance official part number.

Your measuring method is sound.  For cylinders, you want round and minimal taperYour bore measurements are not bad.  The bore readings will keep the rings in alignment with minimal expansion and contraction over the piston travel range.  Your photo indicates that the bore is showing minor "scuff" from either the rings tilting or piston rock (or both).  At this stage, there is no serious damage; however, continued operation would lead to trouble with the excessive piston-to-wall clearance. 

The piston-to-wall measurement should be on your "Y" axis.  The piston is cam ground and has slightly less diameter at the pin (your "X") axis.  This allows for normal piston expansion that results from heat transfer between the wrist pin and the piston pin bosses.  From a practical standpoint, 0.006" piston to wall clearance is too much.  The minor cylinder taper is not the issue, the piston shape(s) are wrong.  There is piston rock and rattle from the variations in piston-to-wall clearance.  This is most noticeable at an idle because the engine speed is lower and the air/fuel mixture is quite lean, with spark timing advanced, while idling unloaded.

Separate the issues:  1) current bores will allow for normal ring seal and reasonable piston-to-wall clearance, 2) pistons are out of tolerance for wall clearance and ring movement, and 3) the piston(s) are distorted, as the wall clearance variations are well in excess of the minimal cylinder bore tapers.  

In the day, we used at least a 3-stone hone to true cylinder bores.  Your glaze breaking was done correctly; however, silicone ball "glaze buster" brushes are notorious for following the bore shape.  You break the glaze but do not true the cylinders.  This gets tricky, because a three or more stone hone will remove more material than the glaze-buster.  Considering your bore diameters and their proximity to OEM specs, I would still use a 3-stone hone and lightly true up the cylinders

I would measure carefully during the honing process to prevent increasing the bore size beyond allowable limits.  If done in-chassis, the crankshaft must be protected from stone/metal debris;  otherwise bearing damage will result.  Clean/wash the cylinder walls thoroughly after stone honing, otherwise abrasive debris will impregnate the cylinder walls.  If done properly, there will be plenty of uniform cross-hatch for ring seating and a lasting finish.  Note that your glaze buster finish is already disappearing.

If you attempt stone honing, the technique that has always worked well for me is to move the hone into the cylinder at a moderate, even pace.  Power still on, withdraw the spinning hone at a reasonably fast speed.  Once you get this honing "rhythm" going, the movement will become familiar:  into the cylinder slower, out faster, repeatedly.  Use a honing oil or equivalent to prevent roughness.  Do not go too deeply and make sure the crankshaft weights are out of the way to avoid stone damage!...You'll get the "cross hatch" pattern desired while knocking off any roughness with the faster withdrawal speed.

Hone examples:

https://www.tooldiscounter.com/product/lisle-cylinder-hone-3-425-inch-range-lis15000 [nice multi-stone hone if you do much of this work; seems a good price for the tool]

https://www.summitracing.com/parts/lil-23500 [lighter tool with less precision but still more effective than a silicone glaze breaking brush; see review comments]

When considering ring seating and honing, I have two anecdotes to share...AMC was having trouble with 4.2L piston ring seating and warranty work in 1987-88.  I was testing YJ Wranglers and picked up a new (800 miles on the odometer) YJ that had the shit run out of it by the previous journalist/tester.  Rings cannot seat under abuse and high engine speeds right out of the gate.  The crankcase oil was down to just under two quarts following the journalist's fast trip from L.A. to the Mammoth Mountain ski area at the Sierra. 

In that era of Japanese engines with higher nickel content iron blocks, little if any break-in was expected.  New vehicle buyers and journalists were clueless about traditional engine break-in techniques.  AMC/Jeep® tried to address the mounting problems by using a very course wall finish on the cylinders to seat the rings quickly or at least prevent cylinder wall glazing, loss of compression and ring oil blow-by.  

Shortly after that test, Mopar® provided a new long-block engine for a project.  I removed the cylinder head for some blueprinting work and could see the course, swept pattern of the cylinder honing.  Obviously, the intent was to seat rings fast and not allow glazing.  Courser honing can be useful for certain engines and operating conditions.  These 4.2L inline sixes, unlike your 2.5L four, had a longer stroke and considerably more piston travel per mile.

You need new pistons, regardless of the honing method.  You could bore the engine block to 0.010" oversize, although that's not mandatory with your minimal taper.  If after honing, the bores remain within tolerance for standard pistons, that would prevent the need for another complete teardown.  United Engine (Silv-O-Lite) pistons would be my choice.  I have traditionally used Silv-O-Lite hypereutectic pistons for stock engines.  Forged pistons required more clearance and can be noisy when cold.  For your usage, forged pistons would be overkill.  Mahle is making Jeep® replacement pistons, if they have a hypereutectic (not forged) type, that would be a consideration.

Keep us posted...

Moses

   

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Well....I bought the Lisle 15000 with a set of course and medium stones. I'm pretty sure the wife is happy I found an excuse to buy another tool! :)

I have used triple stone hones, but nothing like this one.  This thing is going to come in pretty handy.  I have not received my pistons yet (on order), but I did run the hone through lightly (both stones) once.  Most measurements increased on average of one to two ten thousandths.  Now that I have a feel for it, I'll run it again, taking a couple critical measurements along the way.

Referring to the info I posted above, it seems measuring exactly where the manual says, vs. the ring wear pattern is giving me a discrepancy at the top measurement.  Although I measured these with four measurements, I think I'm over-complicating things a bit.  I'm confident the measurements are correct.  I'm not so confident about my measurement location.  I think my "top" measurement is too low in the bore, and my "bottom" might be too high.  My measurements were top/middle/bottom of the visible wear pattern. But...after re-honing I realized this visual indicator is no good because it's no longer present.

So...I'm going to measure with the three measurements described in the manual.  3/8 (10mm) from top and bottom; and use the 2 5/16" measurement (Since it's the center of the bore).  Then I will use those measurements to determine my out-of-round and taper.  On cyl #1 I got quite a different taper using their reference location vs. where I measured at the perceived ring wear pattern.  I think doing it this way will be more precise.  Then I'll go after it with the hone, being careful not to exceed limits, which brings me to a question.  Cyl #1 in the X-axis, middle measurement is 3.8773.  The Y-axis middle is 3.8761.  This gives me an OOR of .0012.  I'll work on this with the hone.  The question is...for piston fitting would I use the 3.8761 or 3.8773 measurement?  Secondarily, do I need to be careful not to enlarge that 3.8773 measurement?  It's largely academic because I'm not "fitting" the pistons with the 'A-F' factory pistons. I just want to make sure I'm within tolerance for standard replacement pistons.  Hopefully that makes sense.  As always...thank-you!  I should have the pistons tomorrow.

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Hi, Wayne...I understand the wife and tool equation.  At our place I/we justify tools by the massive labor sublet cost savings.  Current shop flat rate hourly rates are $100-$160 per hour.  The neighbor across the way called in a mobile service for vehicle work this week.  I overheard (couldn't avoid the decibel level) the argument with the mobile service about the $140 just for the truck to show up—plus $120 per hour thereafter.  Good angle for buying and justifying the Lisle 15000, right?

Congratulations on the Lisle 15000.  This is a professional approach that will true up your bores properly.  The stop at the bottom is helpful, too...Keep in mind my caveat about cleaning the walls thoroughly, they will otherwise impregnate with abrasive.  Keep the crankshaft journals free of debris.  

I like your cautious approach, or you could quickly find yourself at a machine shop for re-boring.  A tip now that you have total control over the truing and removal of material:  The top of the bore has a minor amount of "ridge" or ledge that happens to be round.  If you concentrate your stones in the upper section, placing the upper end of the hone stones just above the bore, you can true up the taper and bring it into shape with minimal material removal.  Take measurements as you proceed.  Watch the honed surface pattern to determine when you have just rounded out the taper area.  Stop as soon as the area is round.  Do not remove material beyond the maximum acceptable bore diameter. 

If you had a lot of taper, you would have to re-bore to true the cylinder.  However in your case, that should not be necessary.  What you want to avoid here is allowing the stones to follow the taper below the ridge, increasing the taper/cross measurement (below the ridge) on your "y" axis.  You get the idea.  When you favor the stones as I'm describing, you will use the top of the bore (which is round) as a guide for the stones.  As you approach round at the "y" taper point, you can begin working the hone the full reach of the bore to remove the least amount of material while making the bore size/diameter uniform.

Overall, you want to round and finish that high-end cylinder without exceeding the 3.8773" diameter if possible.  (Come as close as reasonable.)  The criterion for piston fit is piston-to-wall clearance in any case.  You want your true, round and finished bores to provide the correct tolerance for piston-to-wall measurement.  You can do some homework on actual replacement piston diameters.  No set of Silv-O-Lite pistons will be precisely the same diameters.  (Since cam-ground, diameter is a relative term.)  As we've discussed, and you're thoroughly versed, the concern is the diameter on your "y" axis, as that is the thrust of the piston and skirts. 

As you hint, United Engine may be able to provide "high" side standard pistons with slight diameter differences (within the ten-thousandths of an inch range).  They may simply make all standard pistons on the high side, expecting the installer to hone the bore sizes to fit.  A machine shop of worth will finish hone with a Sunnen CK-10 or equivalent to achieve the desired piston-to-wall clearance.  Production machine shops, or in your case with a stock block, simply staying within the tolerance limit would be sufficient with a new and properly shaped piston and skirts.  You can mix and match a set of pistons based on the minute tolerance differences between each piston. 

Presumably, you're having a machine shop fit your new pistons and pins on the rods?  If necessary, you can specify which new piston should be hung on which rod.  The shop may want to check rods for straight and recondition the rods to the shop's usual standard.  That's up to your request and the shop's findings.  If you're trying to avoid sublet work, you need to follow the protocol for heating the small ends of the rods for pin removal and installation.  We can discuss that step.

I'm pleased (much more than your wife, I'm sure), that you stepped up for this hone.  This is your best shot at truing the cylinders short of a re-bore.

Moses

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Yes sir.  I give her a hard time, but she actually works in the shop with me.  I too justify tools by examining labor charges.  I will be happy to share the figures you provided!

That hone is going to be money.  That was a great recommendation--thanks.  I will follow your tips above for usage.  By the way, is there a 'hard' number I really need to stay under?  I will work on those bores carefully. Apparently my pistons are a bit delayed.  I will be measuring them when they get here. 

I will be hanging the pistons myself.  I plan on heating the rods (using an infrared thermometer). I was planning on building a small jig to set the pins.  Your advice would be most welcome.  Machine shops in my area have so much business right now, they aren't very interested in small jobs without adding a few upsells.  This makes most jobs cost prohibitive on this particular engine.  The upside is my skillset is expanding (and I'm acquiring more tools :) )

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Wayne, I support your idea of doing your own pin fitting with cautions applied.  Of course, you do not want to alter the rods' small end strength by normalizing (essentially annealing) the original heat treatment.  There is a heat threshold/limit to prevent normalizing or removing heat treatment.  Heated pin fitting, done correctly, is way below that heat point.  You are simply expanding the pin boss of the rod ever so slightly, as this is an interference fit pin/bore.

I use Goodson Tool products.  (To preserve your marriage, don't let your wife catch you gazing at a Goodson Tool catalog.)  Review the Goodson commercial rod heaters sold to automotive machine shops.  This one is gas fired and closest to your emulation of the process:  https://goodson.com/collections/rod-heaters/products/gas-rod-heaters.  Make note of how hot the heat gets at the rod small end:  the heat crayon is only 600 degrees F, presumably the maximum heat needed and well below normalizing or annealing if you stop here.  (There is a misspelling in the Goodson catalog listing, they mean "rest" of the rod, not the "red" of the rod.)  You don't want more heat than just the amount necessary for pin fitting.  The small end shape must return to a firm hold on the pin, and the small end of the rod must remain properly heat treated.  You know that already.

Note:  I am a big fan of heat crayons and heat shield paste for my welding and brazing around heat treated parts.  You'll find this video useful, as I prevent a heat-treated vintage axle shaft end from overheating during a high tensile restoration brazing process:  https://www.4wdmechanix.com/how-to-braze-repair-of-damaged-axle-shaft-threads/.  I get my thermal crayons and insulating paste from a welding supply.  I found a Tempilstik at Amazon in 600 degrees F (click here).

Take photos of your jig or apparatus, I'd like to see your approach.  This is not rocket science, and I'm confident you can do this with the use of the infrared thermometer and a heat crayon for insurance.  As far as a bent rod or need to "recondition" the rods, shops usually do this work as an insurance policy.  Done right, there are four steps involved, each requiring precision machine tools...You shared earlier that the bearings showed no uneven or odd wear, a sign of rod irregularities.  If there are no signs of extreme overheating (the OE bearings would have been toast), and you do not plan to sublet/recondition the rods, clean inside the big ends with solvent and Scotchbrite pad.

I would be comfortable with accurately measuring the I.D. of each rod big end with its cap torqued in place.  If you suspect stretched rod bolt threads (measure pitch with a pitch gauge) or have a loose bolt fit in the shank, replace the rod(s) bolts with ARP rod bolts and new rod nuts.  Take care not to distort or damage rod shanks when removing or installing new bolts.  My rule of thumb is that rod bolts that have not stretched or been exposed to extreme heat should be reused.  Performance machine shops replace rod bolts as a matter of routine.  Again, more tools to do it right.

As for cylinder bore sizes, I shared that the new piston set will likely have high and low piston diameter measurements (your "y" axis).  You have the approximate bore measurements and will minimize material removal during the honing process.  If there are significant diameter differences, you will match high (bigger) size pistons with the bores that finish larger.  Use the low side pistons in the tighter bores.  The goal is singular:  You want to finish with the correct piston-to-wall clearances at each cylinder.

The two measurements that concern us are:  1) piston-to-wall clearance (whether running a CK-10 honing machine after re-boring cylinders or performing an accurate stone honing on a stock OE bore) and 2) the piston ring end gaps.  I check end gaps near the top of the cylinder just below the former ridge with the ring squarely aligned.  This should be the widest ring gap point. 

Since service replacement piston rings come "pre-gapped", the manufacturer usually allows for slight cylinder wear while still staying within the allowable gap range.  This is especially true of standard diameter rings, as the block is OE factory bore and likely being re-honed.  Gap filing is mandatory with unfinished rings that require gapping.  Unfinished rings have close gaps, and the installer must file the gaps accurately and squarely to the desired final gap.  This requires a ring gap filing machine or at least a hand crank gap filer (a decent design).  Hand gap files are tedious, the reason that shops use a power ring gap machine.  Pro level power filers with a dial indicator range from $300-$1000, here is a pro-level ring filer:  https://www.summitracing.com/parts/tsr-prf-812dw (cha-ching!).

In your case, pre-gapped rings eliminate the gapping issue.  You're using cast or moly rings?  What brand?  What brand pistons?  You may be planning to re-use the recently installed new rings?  They should have negligible wear.  Check ring condition and the end gaps after cylinder finish honing.  Gaps follow the ring manufacturer's recommendation. 

Since we've spent enough of your money to this point, let's bank on your cylinders, piston fit and ring gaps finishing within the maximum allowable wear.  Rings are forgiving.  Even near maximum allowable gap during assembly, they will provide a good seal over the lifespan of the rings.  Install rings properly, staggering the rings and oil scrapers as per the instructions...As a backup, compare factory data for piston-to-wall clearance and ring gaps to the piston and ring manufacturers' recommendations.  Some pistons have greater expansion rates (certainly true of forged pistons) and are tolerant of greater piston to wall clearance.  Use the piston manufacturer's guideline for correct piston-to-wall clearance.  There is "ideal" and also "allowable" in the case of a standard bore with re-honing.  We can discuss your findings.

Compare OE specs to the ring and piston manufacturers' specs.  The constant here is the finished bore sizes after honing.  (Some photos of the finished stone honing would be useful to others, a comparison with the silicon ball glaze-breaker.)  As we know, since this is a re-ring and new pistons on original bores with some wear, the goal is to finish within the maximum tolerable measurements.

Moses

 

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  • 2 weeks later...

Hello Sir:

Well.  We're up and running (smoothly)  https://www.youtube.com/watch?v=0aW1LGzT4p8&feature=youtu.be

The new hone and pistons did the job!  I'll delineate some of the process below as well as answer the questions you posed.  I have heat cycled the engine a few times and loaded it up on test drives.  I did controlled but hard pulls between 30-50 mph to apply a bit of backpressure to the rings.  It sounds great.  The video above was the first start-up.  In fact I was still filling it with coolant.

Piston pins.  I made a little jig with things I had lying around.  It took about 25 minutes.  I have a tendency to over-engineer most things and spend more time on the process than justified by the result, so I chose to keep this fairly simple.  Once I set the little jig, it worked great.  (pictures below)  I also whipped-up a method to press the old pistons off the rods.  I was confident the rods were fine, but I would not re-use pistons removed with this method (I would have a machine shop press them off if I intended to reuse the pistons).  Prior to using this process on my real pistons and rods, I practiced with about five old sets.  I set the new piston in the jig, heated the rod end to 480° F , brought the rod to the jig (pressed against the left side of the pin bore for indexing) and inserted the pin quickly.   After a few seconds the rod 'shrunk' to the pin and was press-fit.  I then used a bit of oil to pre-lube the assembly with the thought of drawing the oil into the bore.  I don't think I needed the oil, but it reassured me knowing things moved freely with no binding.  I wanted to use as little heat as possible (according to the infrared laser thermometer).  480° F allowed me to move the pins with ease.  (The rod bores all measured within factory spec)

https://youtu.be/CsFiXgt5sMk

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(above piston is a practice piston)

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(sorry about the ginormous pictures...I'm new at this)

I must admit I swayed from your recommended piston-sorry.  I used Engine Tech P3071 Hyperutectic pistons and Engine Tech S38814 Moly rings.  My thought (other than cost) was I was going to re-use the rings I had in the engine since they were essentially new.  These rings matched these particular pistons...so I thought that would be a good idea.

This picture is a bore (from a different engine) I honed with a ball hone.

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The below picture is from this engine with the Lisle hone.  In the photos they look similar, however the Lisle (medium stone) left a much more course surface.  Based on your previous information, I think this finish is better than the ball hone.

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I was able to remove some taper and out-of-round from the bores.  However, I stayed on the conservative side and was still a touch outside factory tolerance.  I was nervous about making the bores too large.  The pistons measured exactly the same so I didn't specify any particular placement.

I think that's about it.  If I missed anything please let me know.  I'm happy to add info or answer any questions.  This is my first time "posting/documenting" to a forum such as this, but I'm hoping others will find the information helpful with their issues.

I didn't even mention the Goodson tools to my better half.  I think I've used up my tool money allotment for this particular project. :) 

Moses, sir, I cannot thank you enough for taking the time to share your experience and walk me through this process.  SEVERAL lesson were learned on this project.  There are several, "I will never...again", moments here.  I am much better equipped for the next one.

This is an incredibly unique forum in that you share your vast knowledge freely and openly.  I didn't mention this earlier, but I actually own two of your books.  I counted on this being a member-to-member forum until I saw all of your expert responses.  Thank you very much! - Wayne

 

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Wayne, you did a fantastic, thorough job!  Slightly outside the maximum in ten-thousandths (I'm guessing, knowing your high standards) is a non-issue with the new piston design.  Nice looking pistons and skirts, tolerances are spot on, too.  Those piston skirts are on for the duration.

Your pin fit method looks great, thanks for the video!  480-degrees F is perfect, obviously enough to increase the small end bore size for pin fit but way below the threshold for heat affecting either the rod or piston!  Emulates the spendy equipment approach, quick and easy with an infrared temperature tool.

This should be a longevity engine.  The start-up sounded great.  Your approach proves the worth of working with tolerances and not jumping immediately into re-machining and the '0.030"' over-sized rebore syndrome.  These engines have thin wall castings and core shift issues, your 2.5L four will run much cooler at stock bore. 

Your work is restorative and fully functional.  Presume you cleaned up the bores without risking of oil contamination at the journals, if washed thoroughly, there will be no embedded (microscopic) material from the honing process.  The photos, which I'm sure are insightful, came through as thumbnails (actually no picture).  You had success uploading photos earlier, if you could please reload these photos, they will be of great value to others.  I'm excited to see how the honing turned out.

You have a trouble-free engine now.  The pushrods at 0.080" preload should work okay, you would know by now.  There should be minimal change in clearance over time.  You now have the tool to measure and fit pushrods correctly on future work.  You have some cool other tools, too, paid for by not removing the engine and subletting it for machine work!

Glad I could jump into your project.  As for time spent at the forums, I instructed Automotive Technology at the adult level and can't leave it alone.  I do not want to discourage others from participating, so this is a delicate dance.  Your approach, questions, earnest effort to do the job correctly and academic curiosity drew me into the project.  I have enjoyed every minute and trust others will benefit from our exchanges!

The topics we covered are valuable to Jeep owners.  I am thoroughly convinced that many later 2.5L and 4.0L engines are running with sloppy pistons.  Our '99 XJ Cherokee 4.0L is likely one of them.  You opened up a valuable subject, and your measurements pointed to the culprit:  piston skirt clearance over time.  There is an obvious issue with the OEM pistons, must be heat distortion as you found no visible signs of skirt "wear".  (There's additional insight from my retired Mopar friend who spoke of several later 4.0L engines that actually "broke pistons".)  Your bores were reasonably "normal" (even truer now!).  The piston skirts and rod bearings showed no signs of bore misalignment with the crankshaft.

As a footnote, in the day we did in-chassis engine overhauls, commonly called a "ring and valve job" in flat rate manuals.  They turned out just fine when tolerances were on specification after honing.  I was a light- and medium-duty truck fleet mechanic in my early career and can attest to successes with these measures.  We commonly did in frame engine rebuilding to a high level, including replacement of the camshaft, lifters, cylinder head rebuilding, cylinder honing, fitting new rings and, in those years, often knurling the original piston skirts back to size.  OEM pistons were that well built, and truck engines were low compression, running on richer/cooler fuel mixtures than today's emission engines.  

The cylinder head machining included head decking (surfacing) if necessary, so head work and piston skirt knurling were often sublet to an automotive machine shop.  As today, three angle valve seat grinding was common to center up and narrow the valve seats.  Stellite replacement exhaust valve seats and nickel-Stellite exhaust valves were truck grade and also used on high performance engines.  Most medium-duty truck engines had OEM exhaust valve rotators. In the late sixties/early seventies, many truck shops had their own valve grinding equipment for in-house work.  I became proficient at operating a Sioux valve grinding machine and seat grinding with stones. 

Standard size rings were actually designed for slight bore increases, and end gap filing was common.  Later, when the engine rebuilding industry took hold, engine components and blocks were sublet to machine shops for the modern, systematic "remanufacturing" of the entire engine.  That was the birth of the every engine gets a 0.030" rebore syndrome.  Large machine shops bought bulk "reman kits" at a lower price point with 0.030" oversized pistons unless an engine required special order larger 0.040" or 0.060" oversize.  Gone were the 0.010" and 0.020" oversizes.  Larger over-bores often do not work well with modern thin wall castings and casting core shift.  Overheating is common.  Many fifties and early sixties engines, even small-block Chevrolets, would tolerate 0.060" and 0.125" oversizes.  We punched 265s and 283s an eighth inch oversize for racing.  The 1955-57 265 blocks became a 283;  the 283 became the popular 301 cubic inches.  For longevity, I would not bore a late 2.5L or 4.0L Jeep engine beyond 0.040", though there is a 4.7L (mathematically more like 4.65L) stroker build at 0.060" over.  The common stroker build is 4.6L at 0.030" oversize.

Cam bearings, as a matter of course, get changed.  Frankly, in the day there was seldom concern for camshaft bearing wear until time for major out-of-chassis engine machining.  Cam bearing wear was usually minimal and not an issue unless clearances became excessive, causing an oil pressure drop.  Today, we all replace camshaft bearings whenever the short block is disassembled;  however, most of the time the OEM bearings are within tolerance.  Yours likely were when you replaced them, which I would have done as well.  I have to make my Lisle camshaft bearing replacement tool pay for itself, right?

Looking forward to your updates...By the way, I'm very curious about your Autel MaxiDAS.  I have looked at the MaxiScope MP408 as a lab scope possibility.  Autel has overcome an apparent stigma around earlier software.  Likely everyone has done so, including Pico.  Your tool is advertised as a highly versatile scanner and works at OEM level with the PCM.  I'm looking at multi-channel wave form, real time tools for drilling down into functions like fuel pump motor wear, in-cylinder pressure transducer "compression testing" and such.  We'll have fun comparing notes...If you are interested and have time, open a new topic at our tools section/forum on the Autel MaxiDAS and your experiences/impressions.  I will follow closely and leave room for others to jump into the exchanges.

Thanks for sharing, Wayne...

Moses

 

 

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Hello Sir.  Thank you for the kind words.  Your depth of knowledge is impressive.  I have "lurked" on these forums for quite some time, gleaning valuable information and insight.  I am not sure what happened to the pictures so I'll try to repost them here.

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Above is the setup I used to press the old pistons off the rods.  (Piston in picture is a 'practice' piston)

Below is the jig for setting the new press-fit pins.

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Below is a block I did with a ball hone earlier this year.

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And finally below is this engine done with the Lisle hone.  The pictures don't capture it well, but the Lisle with medium stone is more course than the ball hone.  The pictures did catch the fact that the ball hone follows the contour of the bores, where the Lisle does not.  I did use the Lisle hone to actually help restore the bore itself where the ball hone simply gets the surface, but has no affect on out-of-round or taper.  This was a great recommendation and I am excited to use it in the future.

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You are correct in that the spec outside factory tolerance was 2-5 ten thousandths.  I may have been able to do more, but I didn't want to chance it.  Reading how you guys used to basically do an engine rebuild with the engine in the car sounds very labor intensive!  This is the first time I've done any honing with the engine in the bay, and that alone was a pain!  Much respect.  It is nice to see someone with your knowledge AND passion for the subject!  Yes.  I have several cool new tools! :)  And they will continue to pay for themselves several times over!  I suspect we both will see several new cam bearings in our future!  

I will move over to the Tools section and post on the scanner.  I am very interested to see your upcoming info on your scope training!

Thanks again!

Wayne

 

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Wayne, I'm thoroughly impressed with your honing pattern.  Rings will seat beautifully, and this engine should run for 200,000 or more miles with the right oil.  Smart move to use the medium grit stones, a good balance...The finish will retain oil without risk of blow-by.  Really nice work and a service to other members and guests.  I thought you'd be impressed with your new Lisle hone!  These cylinders are round and true.  

As for in-chassis engine rebuilding, here's a tidbit.  I worked with a machine shop at the back of a NAPA franchise, common in the day.  The shop had a "portable" cylinder boring bar and portable crankshaft journal grinder.  The bar could bore a single or multiple cylinders in the field.  This machine mounted to the block deck and relied upon the block surface being square to the crankshaft.  (Shimming of the machine's block deck was possible though tedious.)  Like I encouraged with your honing, the crankshaft was protected, in this case from metal debris during the boring process and, ultimately, the finish honing.  The bar had four cutting blades that were adjusted carefully with a micrometer.  The trick was to get the boring bar centered and cutting straight.  The first pass would be a centering cut, then a near finish diameter cut, then honing to size with a hone similar to your shiny new Lisle.  Here is a similar machine at Australia that also mounts on the block deck.  There are new China-built units available at eBay:

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The journal grinder was fascinating.  I looked on eBay and found a photo of the Van Norman "Inblok" grinder.  These units were used in shops or the field.  If a rod journal went out of round or scored badly, the individual throw(s) could be turned with the crankshaft in the block—and chassis.  Most early engines had poured babbitt rod bearings that changed shape with wear.  Many of these engines used shimmed rod caps. Shims could be removed or changed to restore rod clearance—obviously a primitive approach. This worked with engines as late as the 1953 Chevrolet 216 inline six, which also retained its dip-and-splash rod bearing lubrication method with scuppers.

 Winona Van Norman INTHEBLOK Crankshaft Grinder Manual and Parts List 

From the thirties forward, insert bearings gradually became the norm with standard undersizes (0.010", 0.020", 0.030" and 0.040") available following crankshaft regrinding.  For crankshaft polishing or clearance issues, 0.001", 0.002" and 0.003" undersize are also available.  These slight undersizes are a remedy for stock engines like the Ford 300 inline six, which is notorious for excessive rod bearing clearance on a stock, round crankshaft rod journal.  For dealership warranty and service as late as the nineties, Ford recommended mixing these slightly undersize bearing shells to get the right clearance with Plastigage.  I have that procedure in a Ford FSM for F-trucks.  Proper orientation of the thicker and thinner shell half is critical and outlined in the manual.

So you might ask, "What's with boring a single cylinder?"  While you could bore all cylinders to a common standard oversize and replace all pistons, this Depression Era and postwar tool would also allow a low cost single cylinder repair if there was significant damage to just one cylinder—like a failed piston with pin damage to the wall.  You might ask, "So wouldn't that mean one cylinder has more displacement and compression than the others?  Isn't the new piston's weight an issue for balancing?" 

There was little concern when this boring bar was new.  Compression ratios for a Model T were commonly 4.5:1, a Model A was 4.22:1 and a 1932-48 flathead V-8 ranged from 5.5:1 to 6.75:1.  A 1937-53 Chevrolet 216 inline six ranged from 6.25:1 to 6.6:1.  In these lower-speed, low compression, under-square engines with smaller bores, adding 0.010" or even 0.020" additional bore size with an oversize piston to a single cylinder would have little impact on the compression ratio or engine's smoothness.  NVH concerns were several decades ahead.

Moses      

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Hello Sir:

Sorry for the delay.  I had a guy bring me a Jeep that he ran with no oil.  Needless to say it was shot, and it's his daily driver so in the interest of speed, we found him a used motor, tore it down, did some quick checks, and installed the motor.

I pulled-up that individual cylinder boring machine on Ebay.  I didn't know such a tool existed.  That thing is pretty cool.  Processes have certainly changed since you first entered the industry.  Some of the older technology is just genius.  Now THAT is an expense that wouldn't escape the Mrs. Ha!  

I will get some pictures of the Scantool I'm using.  I also have a DRBII for the older Jeeps.  I'll include that tool in the discussion.  I am currently using the PICO, but that was an evolution itself.  Once I get the photos I'll open a post in the tools forum.  I'm a new user to the PICO and Scantool, but they have helped me on a number of issues thus far.

Once again, I really appreciate your help with this engine.  I have learned a lot!

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Hi, Wayne...Sounds like your shop is busy!  The portable boring bars at China are likely found in smaller shops across that country.  If the block deck is square with the crankshaft centerline, this tool would work well and pay for itself quickly.  We're both into pragmatic solutions.  With the block square between the crankshaft centerline and block deck, this bar would work at a smaller shop.  A hone like your new Lisle would finish the cylinders to size.

I'm excited to share that a 4423 Automotive 4-Channel PicoScope kit came up on my radar screen yesterday morning.  I had been waffling between the Pico and Autel, the latter a fraction of the PicoScope's cost.  Pico by all accounts has the best software in the industry, more user friendly and reliable, the promise of free download updates and improvements.  It's British engineering and build quality.

I did some research, and the only significant feature change with the updated and popular 4425A is the floating ground feature in the newer 4425A.  The 4423 was represented as "new" condition, and I purchased it with the usual PayPal plus vendor safeguards regarding authenticity, completeness and function of the package. (Purchased through Mercari, a reputable site as per reviews, though this is first time I have used this source.  Similar to eBay though a more personal process between sellers and buyers.)   I will test the unit upon arrival.  If as represented, I should have a "new" 4423 PicoScope by week's end!

So do open up the tool topic, and we'll discuss diagnostic equipment and its use, best practices and how we "make these tools pay for themselves".  I have worked with the DRB-III, a loan instrument from a Bosch/SPX friend, so I have some experience here.  Despite its great acclaim as a proprietary tool for Chrysler vehicles, the data is dependent on the PCM and its OEM parameters.  I have my own, virtually new StarScan, the orphan between early CAN-bus Chrysler vehicles and PC-based WiTech.

My interest in the Pico and other scopes centers around their ability to read real-time data in useful wave forms.  This interest was elevated by tech webinars conducted at the recent 2020 AAPEX Virtual Experience, a major Las Vegas industry trade show (during SEMA week) that I cover annually.  AAPEX went virtual during the pandemic and had top tuners and diagnosticians conducting these training sessions.  PicoScope was the buzz. 

I also own a classic Sun 720 Electronic Engine Analyzer (late sixties machine with seventies HEI updates) and worked with these oscilloscopes in the day.  (I taught their use at Job Corps in the early eighties.)  I'm a strong advocate for oscilloscope analyzers and believe a PicoScope, used properly and to its potential with transducers and other accessories ($$$), will outstrip the limitations of scan tools and their "pre-selected programs".  So let's do it, Wayne...See ya at the tool and equipment forum!

Moses    

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Hello Sir:

Well my 'shop' was an accidental hobby that slowly became a bit more.  I'll explain in the other forum.  I am all about pragmatic approaches and making tools pay for themselves!

I am really excited about your PICO!  That is a heck of a find!  I also believe you made the smart choice!  I figure, cry once and buy the right tool for the job!  You certainly did that.  I too looked into the Autel a bit but all my research continued pointing me toward the PICO.  If I were a "full-timer" it would have been a no-brainer.  Now you'll never be looking over your shoulder wondering about that PICO!

I have slowly evolved from old-school 'mechanical' to new-school "electronic".  I too have an old scope.  It's a SunScope II.  Well.  I as I write this, I realize I sold it a couple months ago.  I'll throw a picture up in the other forum.

I'll see you on the other side!

 

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