Another Knocking 2.5L Jeep TJ Four-Cylinder Engine

[Tenny]

Hi Moses:

I've researched dozens of these knocking, rattling and ticking Jeep engine cases but after checking mine for similar problems/fixes I haven't found a viable cause to repair.

I started the restoration of a 2000 TJ SE with a blown 2.5(threw a rod out the oil pan).I took on the project after finding a "good" 2.5 with complete running gear from another TJ with rusted frame, no tub.The gentleman I bought it from claimed it ran good with 80k but the frame rust was no longer repairable so he put the tub on another TJ w/4.0 and a rusty tub.

Before installing the good engine, I checked static, cold compression which was 175 psi +/- 10 lbs. I thought this to be good since the engine had not run for over a year.

Everything I checked or replace on the engine indicated it was a sound engine w/ 80k. Once installed in the now restored Jeep,it started right up but had a bad skip on at least 1 cylinder.

I was just about to remove 1 plug wire at a time but the skip went away and it ran good w/ a constant 50+ psi oil pressure hot or cold.I figured maybe a stuck injector or just air in the fuel system caused the skip for the first couple minutes.

I didn't hear any noticeable ticks or knocks for the first several times I started and ran it but when I was about ready to take it out for the first test drive,I noticed a slight knock had developed @ idle only.As soon as I cracked the throttle it went away but came right back @ idle.It was also very present going down hill using the engine to hold me back(5 spd) but was very quiet at idle once warmed up.

I continued to drive the Jeep for 250 back road miles but the knocking got louder @ idle and didn't quiet down as much once up to temp and it still rattles under compression braking

I've tried some of the suggested fixes including sea foam and marvel mystery in oil.I also used a good oil flush as directed and changed the oil to a thicker Rotella T-5 (15w-40) oil.It seemed like that only made things worse.Now it sounds real good and quiet at cold start but begins to knock within 20-30 seconds.

I used a stethascope and listened all over, under and around the engine, including the dist.,timing chain cover and oil pan.I thought the noise was loudest under the valve cover but also on shallow end of pan.I thought no oil on that end might account for that.Just listening to it run with the hood up made me think it was a top end valve lifter/rocker issue.

I removed the valve cover and everything looked good and tight cold.Then I fired it up and ran it til it started knocking and shut it down for a recheck.Everything still looked good and tight and then with the engine was running and knocking, I put pressure on each rocker which made no difference to the knock.There is plenty of oil coming up the push rods and they all spin while the engine is running although a few spin slower then others. I'd already bought new the rockers and push rods hoping that was the problem so I replaced them.Of course that didn't help.

I then removed the oil pan thinking I'd find a loose piston skirt to bore situation but I couldn't get a .002 feeler in while holding the piston to one side all the way down in the bore on any of them.If one slapped I think they all would since they are all the same and that's not the noise I hear

I removed the rod bearings to inspect and they look new, perfect and tight.

I checked for piston pin wear while the bearings where out and everything is tight.I have no excessive or noticeable crank end play.

After removing the timing chain cover,I saw the chain is tight with the adjuster that shows little wear.

The only things I've found is I do need a new distributor as mine has some gear wear and a lot of side play at the rotor end.The gear on the cam looks fine though.

Also I removed the plugs to make turning the engine from under easier and I noticed the cam will move forward and rearward(end play) aprox 3/16" a couple times with every revolution of the crank.

After removing the chain cover I can see that the thrust button on it is shinny as is the center of the cam gear retaining bolt.While turning the engine with the cover off, I can hold the cam from coming forward with my hand with out much pressure.

I was sure the end play on the cam would be my problem but everything  else looks normal.

So to recap my symptoms:

(1) Engine is quiet on start up but knocks within 20-30 seconds.

 (2)   knocking increases with engine RPM's but unsure if 1/2 speed(cam related) or 1 to 1 with RPM(crank related).Going to check that when I get it running again.

 continues to knock but not as load after warm up.

 (3) Rattles while going down hill, engine braking

(4) Removed 1 plug wire at a time while running doesn't effect knock.

(5) Engines runs and starts perfect at all times with great oil pressure and normal coolant temp.

(6) I am running regular gas but it just doesn't sound like spark knock plus it increases with RPM while going downhill, foot off the throttle.

Once I get it going again I will shut the engine off going down hill with the clutch out in gear to see if it knocks then.Not sure what that would tell me but just curious.

I still have the engine apart hoping to find something but will put it together for more testing up top,(lifters) if need be.Also I'll install a new dist. after I've started it to see if it still knock.I'm sure it will.

The one thing that I'm uncertain about is how the cam walks forward to the thrust button then back as I turn it over.It does make a knocking sound when I pry it rearward all the way with pressure.

Does this sound normal?

Thanks for enduring this read.I've been about 3 weeks trying different things and collecting as much info as I could before asking for help.

Tenny

                                            

[Tenny]

I haven't had much interest in this topic yet but I thought I'd go ahead with a update anyways.

Since I found no reason for the knocking I was hear from the crank related parts of my engine, I decided to remove the camshaft and try to figure out what is causing it to move back and forth when rotating the crank from below.I couldn't believe this is normal.

The lifters look and test fine but the cam doesn't look so good.I work in a machine shop so can accurately measure for wear of the lobes.according to the specs of a OEM camshaft,I found that 3 of the lobes are worn to the point that they've lost .022 " of lift and the rest between that and .012 ". I also think I found the reason the cam was walking back and forth while rotating.

2 lobes(#8 & 6)are worn opposite of the way they should be with a .001" taper that would force the cam forward against the button inside the cover.This shows to be the case because both the cam gear bolt and button inside the timing cover show wear.

Then the front 2 lobes(#1 & 2) are worn but still maintain a .001" taper" that would force the cam back to the rear.I read that all the lobes are ground with a .001" taper to keep the camshaft in place. Does anyone know if this is true? It makes sense from the measurements I took at the lobe bases where there isn't any wearing.Each lobe has a .001" taper front to rear (bigger @ the rear) which would cause the lifters to spin and gently encourage the cam to run back where the gear contacts the block acting as a thrust washer. All the other(4) lobes are worn flat with no taper at all just holding the cam neutral.

When looking at the cam and the position of these tapered lobes, it makes since that the cam would walk back and forth while turning under the pressure of the valve springs, which would be greatest when the lobe pushes the lifter up.

As the cam turns, starting @ TDC.# 8 lobe pushes the cam forward.Shortly after,the next lobe to push a lifter up is # 6 lobe which is also the lobe with the wrong taper. Then all of the 4 other lobes to push lifters up in sequence are the ones that are just worn flat, not causing the cam to move front or back.Then when the cam reaches 180 degrees of it's rotation,along comes #1 and a few degrees later # 2 lobes pushing their lifters up(having the proper taper) forcing the cam rearward back against the block where it should be.I believe(and surely hope) this is the knock I could hear when the engine was running.As I'd mention in my first post, I can get a similar  knock when prying the cam rearward when it was still in the engine.

I do have a new camshaft and lifters ordered with a complete timing chain/gear set.I already have new rockers and push rods.Even if this cam swap doesn't cure the knock problem,it needed replacing anyways.I'm blaming the use of zinc free oil for the last half of the Jeeps life for causing the camshaft wear on an other wise good engine.

I'm posting all of this as my "theory" now to convince myself it is my knock problem and will update the actual results once I get the engine running again.I haven't seen any other situations where a worn camshaft was the culprit of a engine knock so I remain skeptical. 

I'm still looking for any info,advice or feedback from anyone that has thoughts and knowledge of the problem of knocking Jeeps.

Thank:Tenny 

 

[Moses Ludel]

Hi, Tenny!  Thanks for the very thoughtful assessment of the 2.5L noise.  I'll add my two-cents with red comments below:

On 6/27/2022 at 6:16 PM, Tenny said:

Hi Moses:

I've researched dozens of these knocking, rattling and ticking Jeep engine cases but after checking mine for similar problems/fixes I haven't found a viable cause to repair.

I started the restoration of a 2000 TJ SE with a blown 2.5(threw a rod out the oil pan).I took on the project after finding a "good" 2.5 with complete running gear from another TJ with rusted frame, no tub.The gentleman I bought it from claimed it ran good with 80k but the frame rust was no longer repairable so he put the tub on another TJ w/4.0 and a rusty tub.

Before installing the good engine, I checked static, cold compression which was 175 psi +/- 10 lbs. I thought this to be good since the engine had not run for over a year.

Good preliminary step...

Everything I checked or replace on the engine indicated it was a sound engine w/ 80k. Once installed in the now restored Jeep,it started right up but had a bad skip on at least 1 cylinder.

I was just about to remove 1 plug wire at a time but the skip went away and it ran good w/ a constant 50+ psi oil pressure hot or cold.I figured maybe a stuck injector or just air in the fuel system caused the skip for the first couple minutes.

I didn't hear any noticeable ticks or knocks for the first several times I started and ran it but when I was about ready to take it out for the first test drive,I noticed a slight knock had developed @ idle only.As soon as I cracked the throttle it went away but came right back @ idle.It was also very present going down hill using the engine to hold me back(5 spd) but was very quiet at idle once warmed up.

I continued to drive the Jeep for 250 back road miles but the knocking got louder @ idle and didn't quiet down as much once up to temp and it still rattles under compression braking

I've tried some of the suggested fixes including sea foam and marvel mystery in oil.I also used a good oil flush as directed and changed the oil to a thicker Rotella T-5 (15w-40) oil.It seemed like that only made things worse.Now it sounds real good and quiet at cold start but begins to knock within 20-30 seconds.

Common enough symptoms...

I used a stethascope and listened all over, under and around the engine, including the dist.,timing chain cover and oil pan.I thought the noise was loudest under the valve cover but also on shallow end of pan.I thought no oil on that end might account for that.Just listening to it run with the hood up made me think it was a top end valve lifter/rocker issue.

I removed the valve cover and everything looked good and tight cold.Then I fired it up and ran it til it started knocking and shut it down for a recheck.Everything still looked good and tight and then with the engine was running and knocking, I put pressure on each rocker which made no difference to the knock.There is plenty of oil coming up the push rods and they all spin while the engine is running although a few spin slower then others. I'd already bought new the rockers and push rods hoping that was the problem so I replaced them.Of course that didn't help.

I then removed the oil pan thinking I'd find a loose piston skirt to bore situation but I couldn't get a .002 feeler in while holding the piston to one side all the way down in the bore on any of them.If one slapped I think they all would since they are all the same and that's not the noise I hear

This was a very good step...

I removed the rod bearings to inspect and they look new, perfect and tight.

I checked for piston pin wear while the bearings where out and everything is tight.I have no excessive or noticeable crank end play.

After removing the timing chain cover,I saw the chain is tight with the adjuster that shows little wear.

The only things I've found is I do need a new distributor as mine has some gear wear and a lot of side play at the rotor end.The gear on the cam looks fine though.

Interesting note on the rotor lateral movement...

Also I removed the plugs to make turning the engine from under easier and I noticed the cam will move forward and rearward(end play) aprox 3/16" a couple times with every revolution of the crank.

After removing the chain cover I can see that the thrust button on it is shinny as is the center of the cam gear retaining bolt.While turning the engine with the cover off, I can hold the cam from coming forward with my hand with out much pressure.

MAJOR INSIGHT.

I was sure the end play on the cam would be my problem but everything  else looks normal.

So to recap my symptoms:

(1) Engine is quiet on start up but knocks within 20-30 seconds.

 (2)   knocking increases with engine RPM's but unsure if 1/2 speed(cam related) or 1 to 1 with RPM(crank related).Going to check that when I get it running again.

 continues to knock but not as load after warm up.

 (3) Rattles while going down hill, engine braking

(4) Removed 1 plug wire at a time while running doesn't effect knock.

(5) Engines runs and starts perfect at all times with great oil pressure and normal coolant temp.

(6) I am running regular gas but it just doesn't sound like spark knock plus it increases with RPM while going downhill, foot off the throttle.

I would run a live fuel trim readout to monitor the A/F compensation under these various conditions.  Each of your knock phases correlates to maximum timing advance, higher manifold vacuum and no engine load.  A scan of the MAP and other related devices could be helpful/insightful.  There is no knock sensor to retard timing under a knock condition, PCM presets are supposed to adjust sufficiently.

Once I get it going again I will shut the engine off going down hill with the clutch out in gear to see if it knocks then.Not sure what that would tell me but just curious.

I still have the engine apart hoping to find something but will put it together for more testing up top,(lifters) if need be.Also I'll install a new dist. after I've started it to see if it still knock.I'm sure it will.

Curious about any gains with the distributor.  Our 4.0L's noise was at the vicinity of the distributor, but #5 cylinder is slightly lower on compression.  Did not replace the distributor, and that noise has gone on for 50K miles.  

The one thing that I'm uncertain about is how the cam walks forward to the thrust button then back as I turn it over.It does make a knocking sound when I pry it rearward all the way with pressure.

Does this sound normal?

When you pry, is the knock coming from the camshaft hitting the rear plug in the block?  (This would be excess movement, obviously.)  Where does the knock emanate from?  If movement is severe enough, is a lobe hitting the adjacent lifter?

Thanks for enduring this read.I've been about 3 weeks trying different things and collecting as much info as I could before asking for help.

No problem, actually intriguing and not uncommon.  Any insight for others is of value.  I'll respond to your second/follow-up reply below...I would emphasize that the use of our Autel MT906TS scan tool has broadened my perspective.  I was bent on finding mechanical errors, which is sensible and your approach, but the scan tool takes live data into consideration.  You can observe changes in sensor readings, timing, fuel trim, MAP, etc., etc., while monitoring the knock.  These changes can point to or help pinpoint causes unrelated to clear mechanical woes.  Enlightening when used properly.  Do you have access to a more sophisticated scan tool?

Tenny

                                            

See reply to your follow-up below...Moses

[Moses Ludel]

Tenny...Here is some fodder for your other post/reply:

On 7/1/2022 at 6:39 AM, Tenny said:

I haven't had much interest in this topic yet but I thought I'd go ahead with a update anyways.

Since I found no reason for the knocking I was hear from the crank related parts of my engine, I decided to remove the camshaft and try to figure out what is causing it to move back and forth when rotating the crank from below.I couldn't believe this is normal.

The lifters look and test fine but the cam doesn't look so good.I work in a machine shop so can accurately measure for wear of the lobes.according to the specs of a OEM camshaft,I found that 3 of the lobes are worn to the point that they've lost .022 " of lift and the rest between that and .012 ". I also think I found the reason the cam was walking back and forth while rotating.

Perfect approach!  This is significant lobe wear...

2 lobes(#8 & 6)are worn opposite of the way they should be with a .001" taper that would force the cam forward against the button inside the cover.This shows to be the case because both the cam gear bolt and button inside the timing cover show wear.

Then the front 2 lobes(#1 & 2) are worn but still maintain a .001" taper" that would force the cam back to the rear.I read that all the lobes are ground with a .001" taper to keep the camshaft in place. Does anyone know if this is true? It makes sense from the measurements I took at the lobe bases where there isn't any wearing.Each lobe has a .001" taper front to rear (bigger @ the rear) which would cause the lifters to spin and gently encourage the cam to run back where the gear contacts the block acting as a thrust washer. All the other(4) lobes are worn flat with no taper at all just holding the cam neutral.

This would stand to reason, and I'm sure your measurements are accurate.  Unlike the AMC inline sixes, including the 4.0L, the 4-cylinder engines require the timing cover button/thrust.  There must be an engineering phenomenon around the camshaft wanting to walk forward on the four-cylinder engine.  The 4.0L and 2.5L are otherwise similar with many interchangeable parts.  The valve spring load phasing could be a factor with the four-cylinder engines and camshaft walk.  Buick V6 engines also require a thrust button.

Importantly, let's consider the relationship between the lifter bases and the lobes.  The lifters, though called "flat tappet", do not have flat bases.  The bases are convex.  So much so that the psi load between the lifter base and the lobe surface is the highest load point anywhere in the engine...I would check the lifter bases.  If they are flat (not convex), you have located a problem.  

From the wear you detected at the lobes (presumably wear measured from the centerline of the camshaft to the lifter peaks), the camshaft and lifter bases are worn substantially.  This could create noise and also valve clearance issues—which you could have confirmed with a CompCams or similar gauge while the engine was fully assembled (just the valve cover removed).  Also, lifter bleed down is always a concern;  this increases valve clearance and makes tappet noise.

When looking at the cam and the position of these tapered lobes, it makes since that the cam would walk back and forth while turning under the pressure of the valve springs, which would be greatest when the lobe pushes the lifter up.

Yes, given your findings, this would make sense...

As the cam turns, starting @ TDC.# 8 lobe pushes the cam forward.Shortly after,the next lobe to push a lifter up is # 6 lobe which is also the lobe with the wrong taper. Then all of the 4 other lobes to push lifters up in sequence are the ones that are just worn flat, not causing the cam to move front or back.Then when the cam reaches 180 degrees of it's rotation,along comes #1 and a few degrees later # 2 lobes pushing their lifters up(having the proper taper) forcing the cam rearward back against the block where it should be.I believe(and surely hope) this is the knock I could hear when the engine was running.As I'd mention in my first post, I can get a similar  knock when prying the cam rearward when it was still in the engine.

Could well be...The loose thrust button would be a contributing factor, allowing the lifter base to "grind off" the taper on the lobe.  If so, you should be able to get accurate lobe height measurements at the region outside (fore and aft) the lifter base's contact zone—unless the lifter base is flattened from wear and has no convex shape.  In that case, the lifter base could be contacting the entire lobe surface.  From your machinist's perspective, imagine the lifter base acting like a cutting tool, flattening the lobe(s) as the camshaft walked back and forth.  There may be an outer margin to that lobe wear area unless the lifter's base contacts and sweeps the entire lobe.

I do have a new camshaft and lifters ordered with a complete timing chain/gear set.I already have new rockers and push rods.Even if this cam swap doesn't cure the knock problem,it needed replacing anyways.I'm blaming the use of zinc free oil for the last half of the Jeeps life for causing the camshaft wear on an other wise good engine.

Fully agree with each of your points...Flat tappet cams suffer woefully from no zinc.  As I noted, the lifter base-to-lobe load is extreme.  (I have 'eighties Sealed Power literature noting a 200,000-plus psi load between the apex of the convex lifter base and lobe.)  A roller lifter camshaft is significantly less stress on the lobes even when running higher valve spring pressure rates.  The roller distributes the load over parallel, much wider surfaces. 

I am very interested in whether this "cures" the knocking.  And yes, you have every reason to replace the camshaft, lifters and timing set regardless of the conclusion.

I'm posting all of this as my "theory" now to convince myself it is my knock problem and will update the actual results once I get the engine running again.I haven't seen any other situations where a worn camshaft was the culprit of a engine knock so I remain skeptical. 

Let's not be skeptical yet.  Your findings are insightful.  Engines get these parts renewed during a rebuild, so the shop or DIY builder can always blame the pistons or some other source for the noise.  You're taking the time to isolate the problem.  This will be telling. 

Assuming that you do not have significant carbon atop the pistons or in the combustion chambers (carbon being unusual for any EFI engine), the remaining possibility, considering the depth of your work to date, would be the unseen piston skirts.  The coatings on these pistons are known to wear off, but you checked for skirt wear in the correct way.  Cylinder taper would be unusual, too;  you could peek look inside the cylinders with a borescope and look for wear and cross hatch...Piston skirts would be a consistent noise and rattle under throttle tip-in or load, not intermittently.  (A loose pin makes a distinct, consistent double-rap noise under slight tip-in.)  Piston noise, typically, would diminish as the engine warms and the piston(s) expand. 

It will be interesting to see whether the decel knocking/noise goes away with the camshaft, lifter and timing chain set renewal...Are you doing the chain guide snubber and spring tensioner, too?  They wear and can be a trouble source, throw off valve timing and allow the chain to rub the timing cover...We shall see!

I'm still looking for any info,advice or feedback from anyone that has thoughts and knowledge of the problem of knocking Jeeps.

On a bright note, if your thorough measurements and insights around camshaft wear and thrust movement do pan out, you have provided a real service to owners vexed with the Jeep engine knocking issue.  I, for one, look forward to your findings.  My 4.0L engine's intermittent idle "knocking" has not progressed or caused an issue in more than 50K miles. 

The 4.0L's noise is at idle only and not consistent.  (As for deceleration engine noise on a grade, there is none, but this is an automatic transmission XJ Cherokee).  Now that you've done this thought-provoking footwork, I would look closer at my camshaft/lifter wear and valve clearances.  The camshaft could be floating, or lobe wear could be at the core of this issue.  Before becoming a "knock", there was an occasional, subtle tappet-type noise.  As a point of interest, and not surprisingly, the noise emanated from the area in line with the distributor...Moses

Thank:Tenny 

 

 

[Tenny]

Thanks for all the input on my engine knock Moses.To be more clear on a couple of points, the cam measurements I took where done as follows:

I mic'ed the lobes on the sides to get the base size(all were the same and correct) then from highest point to opposing side(base) to get amount of lift and compared the measurement to the advertised specs of a OEM cam lift .This is where I observed the lack of lift on all lobes,all to much but some twice as much as others.

Then I mic'ed the 4 cam bearings.The surfaces looked wear free as did the cam bearings in the block.The rear one was 2.00" and they increase in dia. .010" per bearing to the front one on the cam which measured 2.030". I've never replaced a camshaft before but thought this made since for removal/installation reasons ???

Then I put V-blocks under the end cam bearings with a .015" shim(half the total difference in their dia.)  under the small end V-block to bring the cam center line up even with the .030 larger front bearing.

Then with a dial indicator I first checked the base of each lobe and they where all the same showing no wear. They also have what I think is the correct .001 taper(bigger at the rear of each lobe base)which under normal circumstances would help keep the cam towards the rear.They taper is evident on each lobe base as only the rear 1/3 width of each base is shinny with the front 2/3 showing brownish oil color.

It's only at the max lift point of each lobe where things get ugly.I even took a file to the worn tip of the worst lobe since I wouldn't be reusing it to see if the case hardened surface had been worn through.It still seemed to be present but must be very thin.

The lifters actually looked and seemed to test OK although I'm replacing them of course.After pulling them from the engine which hadn't been run for 2 days, I couldn't compress any of them.They do have a slight concave base of less then .001" and measure the same height as well looking shinny and pit free.

The knocking noise I could recreate was by prying the cam rearward.It only moves about 3/16" front to back so I'm sure it not hitting the rear plug.The noise is when the back side of the cam gear hits the block with a little force,more then it should while running in normal conditions.I'm hoping the sudden back and forth motion of the cam that I observed while rotating the crank is causing this abnormal front to back force, enough to cause a knock.???

I am replacing the snubber and tensioner  even though the ones I removed show very little wear.The chain needed about 1/2 of the tensioner's total travel to keep it tight and the snubber has hardly been touched.

The cam gears do look a little sharper at the points then I've seen on other engines but will know better when I can compare them to the new cloyes set coming.

It is strange how the engine went from "no bad noises" for the first few start ups then to a slight knock only at idle that went away when warmed up to where it is now.

It did seem to be worse after using a quality engine oil flush as directed and then changing the oil and filter to Rotella T-5 15W-40. I've read others have had some success doing this but not me.I also used seafoam in the gas and through the throttle body as directed but noticed no change.Runs real good though.

It always had the rattle/clatter when letting off the throttle going downhill. It reminds me of a rattle that a little 48 CJ-2A had that I used to have when pushing the clutch on it to shift but I knew it had a bad throw out bearing.My noise now is from the engine and goes back to the knock when I push the clutch, allowing the engine to idle.

It's possible the two different noises are two different reasons.

If the engine still knocks after the cam,lifters,chain,gears and distributor replacement, I'll spend more time checking for other causes.If nothing is found then I'll remove the engine and hone it, install new pistons and anything else that doesn't look right.

This little Jeep was a worthy project that needed saving.It looks and drives real good and I plan to sell it so the noise has got to be found at all costs.

I'll get back with results after the cam install as soon as it gets here.

Thanks again: Tenny

 

[Moses Ludel]

Some comments below, Tenny...

3 hours ago, Tenny said:

Thanks for all the input on my engine knock Moses.To be more clear on a couple of points, the cam measurements I took where done as follows:

I mic'ed the lobes on the sides to get the base size(all were the same and correct) then from highest point to opposing side(base) to get amount of lift and compared the measurement to the advertised specs of a OEM cam lift .This is where I observed the lack of lift on all lobes,all to much but some twice as much as others.

Then I mic'ed the 4 cam bearings.The surfaces looked wear free as did the cam bearings in the block.The rear one was 2.00" and they increase in dia. .010" per bearing to the front one on the cam which measured 2.030". I've never replaced a camshaft before but thought this made since for removal/installation reasons ???

Then I put V-blocks under the end cam bearings with a .015" shim(half the total difference in their dia.)  under the small end V-block to bring the cam center line up even with the .030 larger front bearing.

Smart and needed with the step sizes of the journals...

Then with a dial indicator I first checked the base of each lobe and they where all the same showing no wear. They also have what I think is the correct .001 taper(bigger at the rear of each lobe base)which under normal circumstances would help keep the cam towards the rear.They taper is evident on each lobe base as only the rear 1/3 width of each base is shinny with the front 2/3 showing brownish oil color.

Again, you're thorough, and is accurate...

It's only at the max lift point of each lobe where things get ugly.I even took a file to the worn tip of the worst lobe since I wouldn't be reusing it to see if the case hardened surface had been worn through.It still seemed to be present but must be very thin.

Initial case hardening is typically 0.030"-0.035" for this kind of part.  I use Fowler hardness files (a set) to confirm surface hardness in HRC.  As you suggest, the case is likely thin on the high wear lobes.

The lifters actually looked and seemed to test OK although I'm replacing them of course.After pulling them from the engine which hadn't been run for 2 days, I couldn't compress any of them.They do have a slight concave base of less then .001" and measure the same height as well looking shinny and pit free.

Lifter bases should be convex or arc'ing outward slightly...When there is a cam-to-lifter lobe issue or a cam goes "flat", the damage is typically concave or dished wear into the lifter base.

The knocking noise I could recreate was by prying the cam rearward.It only moves about 3/16" front to back so I'm sure it not hitting the rear plug.The noise is when the back side of the cam gear hits the block with a little force,more then it should while running in normal conditions.I'm hoping the sudden back and forth motion of the cam that I observed while rotating the crank is causing this abnormal front to back force, enough to cause a knock.???

Worth mentioning, Manley, Cloyes, CompCams and others make aftermarket spring loaded thrust buttons.  (Buick V6 engines have a spring loaded, rotating button with the stock timing sprocket and camshaft.)  Since the slight taper of the lobes ramp toward the rear of the camshaft, the natural tendency, as you note, would be to push the camshaft rearward and also to rotate the lifters.  There is no thrust plate (between the cam sprocket and block) on a Jeep 2.5L, so the cam gear/sprocket rides against the block face.  The pressure is not high enough to wear the block's face significantly.  This is more to keep the sprockets aligned.

I am replacing the snubber and tensioner  even though the ones I removed show very little wear.The chain needed about 1/2 of the tensioner's total travel to keep it tight and the snubber has hardly been touched.

Just a wise precaution here...

The cam gears do look a little sharper at the points then I've seen on other engines but will know better when I can compare them to the new cloyes set coming.

Cloyes is a wise choice and proven quality...A double roller chain is superior and provides far more accurate valve timing when wanted...

It is strange how the engine went from "no bad noises" for the first few start ups then to a slight knock only at idle that went away when warmed up to where it is now.

This does raise concerns.  How did you flush this engine and with what agent?  Is there a possibility that the flushing compound provided too little protection between the lifters and cam lobes?  How long did the flush go on?   Could the lifters have worn into the lobes during this flush?

My other concern is spark timing and fuel trim/injector flow...I actually invested in an injector cleaning and testing machine to rule out uneven or erratic injector flow rate concerns when tuning and troubleshooting EFI engines.  I bought the Autool CT200 for around $400 at the time on eBay.  This has proven smart for accurate diagnostics and troubleshooting.  Again, a good way to separate mechanical issues from fuel-and-spark management issues.  Here's the machine:  https://4wdmechanix.com/jeep-4-0l-ignition-tune-up-and-injector-cleaning/.  

Have you run a fuel rail pressure and fuel flow volume test on this engine and chassis?  Are there any check lights?  Although I weigh Jeep OBD-II MIL readings and DTCs with caution, they can be a place to start.  A good scan tool will provide clearer findings.

It did seem to be worse after using a quality engine oil flush as directed and then changing the oil and filter to Rotella T-5 15W-40. I've read others have had some success doing this but not me.I also used seafoam in the gas and through the throttle body as directed but noticed no change.Runs real good though.

I use SeaFoam for the SUR&R FIC903 and 203 cleaning processes.  This is good for on-the-engine but is short of testing the flow rate/volume of the injectors.  Here's an FIC203 cleaning on the engine, which did cure knocking as described.  Carbon build-up on the piston crowns can contribute to knock, especially when running 87-octane Brand-X gasoline without anti-knock or cleaning additives.

It always had the rattle/clatter when letting off the throttle going downhill. It reminds me of a rattle that a little 48 CJ-2A had that I used to have when pushing the clutch on it to shift but I knew it had a bad throw out bearing.My noise now is from the engine and goes back to the knock when I push the clutch, allowing the engine to idle.

It's possible the two different noises are two different reasons.

Sounds like it...As I've hinted, If you have access to a quality scan tool that can stream and capture live data while driving, it would be useful to observe the engine sensor functions while this knock occurs.  Determine whether or not fuel-and-spark timing management is involved.

If the engine still knocks after the cam,lifters,chain,gears and distributor replacement, I'll spend more time checking for other causes.If nothing is found then I'll remove the engine and hone it, install new pistons and anything else that doesn't look right.  

I would do a borescope peek in the cylinders to see if there is much carbon buildup on the piston crowns or combustion chambers.  These engines work hard, and carbon knock can be a factor.  Consider, too, that the piston loads are higher under deceleration/compression braking.  This can create piston rocking. 

Consider checking the valve spring heights and seat pressures.  (If necessary, you can use an air hold and carefully remove valve springs with the head still in place.)  Inspect for guide/stem clearance issues or possible valve seating noises.  (A full inspection of seats and valve faces would require cylinder head removal.)  Also check for exhaust back pressure issues if the problem persists.

This little Jeep was a worthy project that needed saving.It looks and drives real good and I plan to sell it so the noise has got to be found at all costs.

I'll get back with results after the cam install as soon as it gets here.

Sounds good, Tenny...Moses

Thanks again: Tenny

 

 

[Tenny]

Hello again Moses:

The oil flush I used was Liqui Molly pro line engine flush.It has great rating's and cost more then most so it must be good.The oil in the engine at first was 10W 30. After 250 easy back road miles,(probably 8 hrs run time) I figured the knock wasn't going away on it's own.I drained 1 qt. of hot oil from the engine and added the flush. I followed the instructions (start and idle engine for 15-20 mins then change oil and filter) After filling and installing a new oil filter, I filled the engine with diesel Rotella 15W 40 oil because I read it still has zinc in it for flat tappet lifters(is this a good idea ?).I also added 4 oz of Marvel mystery oil.

Before starting it back up I pulled off the coil wire and cranked the starter a few times until I had oil pressure.I then started it and after about 30 sec. it still had the knock but seemed to be louder now. It could have been the natural worsening of what ever is causing the knock since it had some added run time. Hard to be sure. I do know the entire inside of the engine is now spotless and the valve train free of any sludge.

When I drained and dropped the oil pan to check the piston skirts, I did notice about a 1/2 tea spoon full of black,crunchy carbon deposits +/- the size of a pencil tip in the bottom of the pan.I ran a magnet in the drained oil and pan but didn't get any thing on it so I know there wasn't any steel nor was there anything shinny.The deposits could be crunched between my thumb and finger leaving a black smudge so I don't think they were the chain tensioner ether. I thought the oil flush or running Seafoam through the throttle body may have cleaned these deposits from the internals.There was also some in the drain pan as well when I dumped it.

I cut open the first oil filter(the one w/250 miles on it) and found no metal or debris in it.

Oil pressure has always remained steady around 50+ psi. even @ hot idle.

I haven't had any CEL's and did scan for codes but have none present at this time.

While the Jeep was running and knocking, I've removed the plug wires one at a time (twice) and it didn't affect the knock.Would this rule out a injector, carbon build up or other spark/ fuel knock issue? I am going to use this problem as an excuse to get a borescope. It would be helpful in many projects I get involved with.

If good lifters are slightly convex then my old lifters do have some wear since they do have a slight concave(dish) shaped base.I believe since all of the cam lobe bases were shinny only on the rear 1/3 portion, the lifters have been worn this way for a while.If they were convex it seems the would have shined up the middle of the lobes, not just the edge. 

As I mentioned earlier,the old distributor I removed had about 1/16" of side movement at the rotor end but none at the gear end.I plan to remove the shaft from the housing and gear from the shaft to use it in a drill to prime the engine with oil before starting with the new cam and parts. 

When I ran the engine without the rocker cover trying to locate the knock, I did notice 4 push rods spun very fast and 4 much slower.They would be the 4 with the non tapered wear on the high point of the lobes. I did have lots of oil quickly coming up to the rockers. Also putting pressure on 1 rocker at a time didn't affect the knock ether.

These are all just thoughts and observations to keep me busy while I wait and wonder until the new parts arrive.

Until that time: Tenny 

 

 

[Moses Ludel]

Tenny...Thanks much for sharing these details.  You were thorough in your approach as usual...Some additional thoughts and quips below:

On 7/6/2022 at 2:41 PM, Tenny said:

Hello again Moses:

The oil flush I used was Liqui Molly pro line engine flush.It has great rating's and cost more then most so it must be good.The oil in the engine at first was 10W 30. After 250 easy back road miles,(probably 8 hrs run time) I figured the knock wasn't going away on it's own.I drained 1 qt. of hot oil from the engine and added the flush. I followed the instructions (start and idle engine for 15-20 mins then change oil and filter) After filling and installing a new oil filter, I filled the engine with diesel Rotella 15W 40 oil because I read it still has zinc in it for flat tappet lifters(is this a good idea ?).I also added 4 oz of Marvel mystery oil.

The Rotella certainly would not hurt anything, though the 15W is high for cold weather start-ups.  I use 10W-40 in the 4.0L in the summer, 5W-30 in the winter if parked outside without using the block heater.  When the block heater is in play, I use 10W-40 year round..Marvel Mystery Oil won't hurt anything, either;  the product has been around forever.  I used it in the late sixties on carbureted light truck engines that really benefited from Marvel Mystery Oil and Rislone. 

Before starting it back up I pulled off the coil wire and cranked the starter a few times until I had oil pressure.I then started it and after about 30 sec. it still had the knock but seemed to be louder now. It could have been the natural worsening of what ever is causing the knock since it had some added run time. Hard to be sure. I do know the entire inside of the engine is now spotless and the valve train free of any sludge.

When I drained and dropped the oil pan to check the piston skirts, I did notice about a 1/2 tea spoon full of black,crunchy carbon deposits +/- the size of a pencil tip in the bottom of the pan.I ran a magnet in the drained oil and pan but didn't get any thing on it so I know there wasn't any steel nor was there anything shinny.The deposits could be crunched between my thumb and finger leaving a black smudge so I don't think they were the chain tensioner ether. I thought the oil flush or running Seafoam through the throttle body may have cleaned these deposits from the internals.There was also some in the drain pan as well when I dumped it.

Solid carbon of "crunchy" variety could be simply the slough from hot (oil cooled) areas of the block.  The result of carbon loosened from piston crowns or combustion chambers is unlikely, as that carbon would pass out the exhaust and not get past the rings.  More likely, this stuff was from the cylinder head valve spring areas, timing case or main caps, the hottest spots in the engine.  As you note, the flushing could have loosened this carbon and sent it to the oil pan.

I cut open the first oil filter(the one w/250 miles on it) and found no metal or debris in it.

Consistent with your bearing inspection and other observations that you have shared...

Oil pressure has always remained steady around 50+ psi. even @ hot idle.

I haven't had any CEL's and did scan for codes but have none present at this time.

While the Jeep was running and knocking, I've removed the plug wires one at a time (twice) and it didn't affect the knock.Would this rule out a injector, carbon build up or other spark/ fuel knock issue? I am going to use this problem as an excuse to get a borescope. It would be helpful in many projects I get involved with.

Would rule out piston slap (rock at the skirt), mainly.  Could also reduce a loose connecting rod or piston pin noise.  This would eliminate a lean knock, too.  A fuel trim check could troubleshoot for a lean knock.  Simply reading the spark plug coloration is helpful if the compression is uniform.

Again, this is why I like the CT200 injector cleaner and flow test machine.  I am able to confirm whether the injectors flow properly.  I saved a bundle after cleaning my OEM/original 4.0L injectors with the ultrasonic cleaner phase of the machine and installing new filters.  Fortunately, the flow tested uniformly and as new on each injector, and I could take the injectors off the troubleshooting list.  I avoid using off-shore Brand-X type injectors, and new genuine OEM Bosch or Siemens injectors can get quite pricey.  The machine nearly paid for itself the first time I used it.  It will amortize with a couple of injector cleanings.

You will really like the borescope.  They can be bought for well under $100.  Daily use pro grade scopes with more recording and optics features cost more.

If good lifters are slightly convex then my old lifters do have some wear since they do have a slight concave(dish) shaped base.I believe since all of the cam lobe bases were shinny only on the rear 1/3 portion, the lifters have been worn this way for a while.If they were convex it seems the would have shined up the middle of the lobes, not just the edge.

Yes, that would be the case.  That's also a lot of camshaft wander, as you have noted.  According to the wear pattern, the camshaft is walking forward, toward the timing cover.  The lifter/lobe wear and thrust button would be involved.  The timing sprocket is moving outward from the block and not staying in alignment.

As I mentioned earlier,the old distributor I removed had about 1/16" of side movement at the rotor end but none at the gear end.I plan to remove the shaft from the housing and gear from the shaft to use it in a drill to prime the engine with oil before starting with the new cam and parts.

Good use of worn parts...Why waste a "primer tool"? 

When I ran the engine without the rocker cover trying to locate the knock, I did notice 4 push rods spun very fast and 4 much slower.They would be the 4 with the non tapered wear on the high point of the lobes. I did have lots of oil quickly coming up to the rockers. Also putting pressure on 1 rocker at a time didn't affect the knock ether.

Pressure on each rocker was a good test for valvetrain issues...The spinning pushrods would be characteristic of distinct lobe wear and valve clearance issues.  A CompCams gauge ($20) is a must for selecting pushrod lengths and also serves well to troubleshoot valve clearance issues like lobe wear or, going the other way, valve seat recession.  Part of your thorough valvetrain renewal should include a check of the pushrod lengths with a CompCams or similar gauge.  If valve face wear and seat recession are minimal, renewing the camshaft lobe and base heights should permit reuse of the original pushrods if still in good condition.  Verify lengths and fit to each valve accordingly. 

These are all just thoughts and observations to keep me busy while I wait and wonder until the new parts arrive.

Until that time: Tenny 

You're separating piston/rod and block (cylinder bore size/shape or core shift) issues from valvetrain noise, a good move...If the noise is valvetrain related, the new camshaft, lifters and timing chain set will do the trick as long as the valves, seats, valve guides and springs are in good condition.  I would install a new or upgrade thrust button as insurance against camshaft walk...I am very interested in your findings after this work!

Moses

 

 

[Tenny]

Hello again Moses

I finally got my new camshaft,lifters and timing set and distributor installed and much to my disappointment the knock hasn't changed.I held out hope while the engine was at fast idle for 20 mins. breaking in the cam but as soon as it was brought back to normal idle the knock was still there.

I did some more testing and am quite sure it is coming from a piston.I once again removed plug wires 1 @ a time and it did seem like # 4 made a little less knock.If I reved the engine quickly the knock would subside some but when I let it return to idle it would make the clatter until the engine slowed which is what I hear when engine braking while driving.

I also unpluged 1 injector @ a time and got the same results, a little less knock but not gone.I did do a static comp. test on the engine warm this time and had 160 psi on #'s 1 & 2.On # 3 I had 150 and # 4 @ 175.Interesting the suspect problem cylinder has the most psi. Maybe a lot of carbon ? I'll find out tonight. Even though I thought everything looked good on the bottom something isn't.

So now the little engine is back out and on a stand waiting to be disassembled.I would like to do a pressure leak down if I can get a tester in time.The borescope I ordered did come in and I'm going to use it tonight.I want to get to the bottom of the noise but I'm not disappointed that I had to remove the engine.It did have a bad rear main seal leak that didn't show it self until ran for a while.

As far as the running part of the engine with the new camshaft and parts, it runs great but it always did.It does have a better idle now. Before it would have a slight uneven idle once in a while. Maybe the bad dist.?

At least I know it will continue to for a long while to come when I'm done.

I'll update once I get into it.

Thanks for your help.Tenny   

 

[Moses Ludel]

So, this is telling, Tenny...I applaud your tenacity and ambitious pursuit of the knock source...Reading through your findings carefully, I believe you have excessive carbon in #4 cylinder.  175 psi at this mileage would only be possible with carbon.  Like you note, a leakdown test could compare each cylinder's ability to seal, which would bring the compression comparison more into focus. 

The new borescope should reveal considerable carbon on the crown of the #4 piston, possibly a coating on the combustion chamber as well.  Let us know what you think of the borescope.  Short of cylinder head removal, this tool provides clarity during in-depth engine troubleshooting. 

If you do find considerable carbon, enough to explain a carbon knock, the logical step is to remove the cylinder head, easy enough on the engine stand, and de-coke the piston crowns and combustion chambers.  Note the cylinder wall condition, the crosshatch and any taper.  If you suspect the rings have wear, this is clearly the time to pull the rods and pistons, hone the cylinders, wash the cylinders carefully and install new rings.  Measure pistons carefully for round, wear and any skirt issues. 

The skirt coating is especially worth noting, it is notorious for wearing off.  Cracked skirts have been noted on many 4.0L engines, possible on the 2.5L and worth considering.  Engines generally do not carbon knock under deceleration, especially EFI engines that virtually shut off the fuel flow.  Piston skirt condition is clearly a consideration.

If you do just the de-coke procedure, after reassembly, perform a leakdown test for a clean slate reading of cylinder seal.  Cranking compression is nowhere near as accurate as a leakdown test.  Make sure there is no loose carbon or debris present before performing a leakdown test.  As you de-coke the pistons, vacuum away debris.

A good review about now is my exchange with "Wayne".  He had very good success with his in-chassis overhaul of a 2.5L TJ Wrangler engine.  The work would be much easier on the engine stand: 

Keep us posted and thanks for sharing!

Moses

[Tenny]

Back again for a update Moses.

Even though I knew I'd be removing the head, I  did get the borescope  and checked into each cylinder bore before taking off the head.

I didn't see much carbon build up but could see some scuffing on the cylinder walls.I could also see some cross hatch left but not where the scuffing took place. All in all the borescope will be a handy tool to have for future issues.

Once the head was off, I confirmed what I saw with the scope. Not much carbon but plenty of scuffing on all bores.Much like the earlier posts from Wayne who had almost identical symptoms, I could duplicate a knocking noise by moving the top of the piston side to side near the top of the bore( aprox. .0010" of side movement).

Then I removed the oil pan again and could now slide a .003" feeler gauge between the skirt and the bottom of the bore.Much easier to do now that the engine was out and upside down.

I then used platigage to check the rod bearings for clearance.All have .0015 clearance except # 2.It has only .001.

I noticed rod bearing shells # 1 & 2 have a .001 stamped on the back with the 3 & 4 shells having std on them. Now I know why the bearings looked like new, they were.

I assume the PO was in there trying to correct this knock along with installing a new timing chain and gear set because they also looked new.At least the crank looks good.

Once I removed the pistons I could see the full extent of scuffing on them and the bore walls.As bad as the walls look, I can't feel the scuffing marks with my finger nail.

I now attempted to measure the amount of wear even though I haven't got a proper bore gauge yet. I've ordered one but it's a week away.

I used a telescoping ID gauge to get a idea if a over bore is called for and I'm afraid it is. After 2 hrs. of measuring and remeasuring it seems I'm outside the acceptable limits.

All 4 bores measure 3.878 down 3/4" from top.

Then measuring down in the bore 2-1/2", the #'s 2, 3 & 4 measurement increases .001 to 3.879 but # 1 is only 3.876. Once again I wonder if the PO honed and installed new rings on the old pistons which would account for some remaining cross hatch and great compression. I also can't explain why # 4 has 175 psi cranking compression.I'm going to try another gauge once the engine is running again.A bad gauge is the most likely culprit.

The bores do seem to net the same results when I measure across them in line with the crank so they do appear to be round.Once again, even after much remeasuring to get consistent numbers, I'd be more confident if I had a true bore gauge if it's the difference of a overbore or just a hone job.    

Then I looked at and measured the pistons.Once again I wished for the proper tool(bigger mic) but had to use my oversized dial calipers instead. I can't find these special tools around here with out ordering them.

I took 3 measurements on each piston. 1 at the very bottom across the skirts (A). 1 across the middle at the center line of the pin (B) and the last 1/4" below the bottom ring(C).

Measurement A(across skirt) is 3.872 on all 4 pistons.

Measurement B( across middle)  is 3.874 on all four.

Measurement C(just under rings) is 3.870 on #2 & #4 and 3.869 on #! and 3.868 on #3. Not sure what new pistons would measure but this seems a bit undersized as indicated by the rocking type wear and scuff marks.

Probably the source of the knocking wouldn't you think. 

I've added a few pictures of the worst worn areas including a view of the head.I noticed intake valves on #'s 3 & 4 are darker colored then the others.This is both sides of the # 3 piston which is the worst but the others aren't much better.

The top of the #4 piston(175 psi comp.)  was this clean when I took off the head.

It may be that I'd been testing for the knock source with the engine running by removing the plug wires on these two cylinders as well as unpluging the injectors just before shutting it down.

If my bore measurements are correct and bores are already honed oversize, I'm most likely looking at a bore job.Would you agree or are slightly oversized pistons available to correct my problem ?

In the meantime I'll move onto another project until proper measuring tools arrive.

Thanks again: Tenny

   

[Moses Ludel]

Tenny...You clearly found the knocking source...See my comments below...Congrats!

6 hours ago, Tenny said:

Back again for a update Moses.

Even though I knew I'd be removing the head, I  did get the borescope  and checked into each cylinder bore before taking off the head.

I didn't see much carbon build up but could see some scuffing on the cylinder walls.I could also see some cross hatch left but not where the scuffing took place. All in all the borescope will be a handy tool to have for future issues.

Turned out not to be carbon, but you have a great diagnostic tool going forward!  Can't see piston skirts with a borescope, but the cylinder wall appearance was a distinct tip-off once the pistons were lowered in the cylinders.  The borescope did its job, a sound investment.

Once the head was off, I confirmed what I saw with the scope. Not much carbon but plenty of scuffing on all bores.Much like the earlier posts from Wayne who had almost identical symptoms, I could duplicate a knocking noise by moving the top of the piston side to side near the top of the bore( aprox. .0010" of side movement).

Another clear tip-off...0.0013"-0.0015" would be "ideal" piston to cylinder wall clearance;  0.0013" to 0.0021" is acceptable...A 0.010" piston-to-bore clearance is a red flag—not possible to know until you have removed the head.

Then I removed the oil pan again and could now slide a .003" feeler gauge between the skirt and the bottom of the bore.Much easier to do now that the engine was out and upside down.

The pistons are shot (great photos, Tenny), so this measurement likely varies between pistons.  If this were the minimum gap, it would be slightly loose.

Yep, everything gets easier on an engine stand...When possible, that's the place to do the main seal, too.  We can change them from the floor but not as easily!

I then used plastigage to check the rod bearings for clearance.All have .0015 clearance except # 2.It has only .001.

The crankshaft journals can now be checked for round.  These cranks hold up well with use of clean oil and constant oil pressure.

I noticed rod bearing shells # 1 & 2 have a .001 stamped on the back with the 3 & 4 shells having std on them. Now I know why the bearings looked like new, they were.

Umm...Measure the journals for round and diameter, fit bearings accordingly if you're not turning the crankshaft.  If round, no scoring and clearanced properly, that would work.

I assume the PO was in there trying to correct this knock along with installing a new timing chain and gear set because they also looked new.At least the crank looks good.

Yep, crank sounds okay but confirm with a mic..."Interesting" how the PO addressed the knocking without accounting for the piston skirt damage...Is the visible silicon ball honing visible only at the upper cylinders or does it run to the bottom of the bores?  Curious whether the rods/pistons were removed during the PO's work.  Are these the OEM piston rings with wear?  They look like it...

Once I removed the pistons I could see the full extent of scuffing on them and the bore walls.As bad as the walls look, I can't feel the scuffing marks with my finger nail.

Wayne was fortunate, too.  Without taper, and if you can hone to spec without increasing the bore too much, Standard pistons and rings are possible.  Wayne had that good fortune.  Do you have a quality hone like the Lisle that can also true the cylinders and offer more control?

I now attempted to measure the amount of wear even though I haven't got a proper bore gauge yet. I've ordered one but it's a week away.

Good path, Wayne went down it...Here's the good news:  Like Wayne and me, you invest in tools instead of staggering monthly vehicle payments.  Every tool in my shop has paid for itself many times over.  We have saved a bundle over the years by not updating vehicles.  Our vehicles each have a rigid preventive maintenance routine (mine) and get repaired before damage accrues.  You likely value this approach as well.  Willingness to contribute your elbow grease makes this work.

I used a telescoping ID gauge to get a idea if a over bore is called for and I'm afraid it is. After 2 hrs. of measuring and remeasuring it seems I'm outside the acceptable limits.

All 4 bores measure 3.878 down 3/4" from top.

I did some research.  Mopar offered Standard pistons up to sizes "E" and "F".  These are slightly larger diameter but still considered "Standard" piston sizes.  "High side" OEM Standard pistons were available for dealership/warranty service work.  Likely neither piston (E or F) is available today;  warranty work would be a short or long engine replacement.  Here are the Mopar part numbers for each piston in case NOS parts exist at eBay. (See my comments below about United Engine and high side Standard pistons.):

04798332 AR EP0 (TJ era 2.5L) E Size Piston, 3.8758" diameter for a maximum bore size of 3.8775"
04798333 AR EP0 F (TJ era 2.5L) Size Piston, 3.8762" diameter for a maximum bore size of 3.8779"

Add 0.0013"-0.0021" (maximum) to these piston diameters to determine the finished cylinder bore sizes.  The F size pistons would actually tolerate a finished and round bore diameter of 3.8783" if you do the math for Mopar's maximum acceptable piston-to-cylinder wall clearance.  The "F" pistons would work if your hone just reaches the current 3.878" size in the cylinders.  A few 10,000ths of an inch past the 3.8783" (maybe to 3.8785" or so) would still work without an issue, especially with coated pistons.  I would hone and true the four cylinders, come up with a high side Standard bore size that works, then contact United Engine to see whether they can furnish a piston set to meet your specifications.  If they cannot, it's time for a rebore of the four cylinders and oversize pistons.

Mopar Note:  Do not measure moly coated pistons!  This source is the Mopar 1998 TJ Wrangler FSM.

Light honing/truing must reduce taper to a maximum of 0.001".  0.001" is also the maximum acceptable out-of-round for the cylinders.  In my exchange with Wayne, see the January 26, 2021 comments on contacting United Engine about "high side" Standard pistons.  If you could find pistons to fit (proper piston-to-cylinder-wall clearance), the ring gaps need attention.  (Bore circumference and radius would change very little during the honing, so piston rings should still fit the cylinder wall radii.) 

The factory tolerances for ring gaps are wide on these engines.  If pre-gapped rings measure too wide (which would be surprising), ungapped piston rings are available for hand sizing the gaps to specification.  Hand gapping tools are a real chore;  a power ring file, used carefully, works best for this task...All of this plus piston pin removal and fitting (see the Wayne exchange) would be necessary if you do not rebore the block or sublet the work.  Thorough cleaning of the block and removing all honing debris is critical.

If you cannot find high side standard pistons of the correct diameter, it would be smarter just to sublet a rebore and hone job to a local automotive machine shop.  (Let them hot tank the block, which will require new cam bearings.)  You would want to provide (or have them provide) the pistons to be carefully fitted during the honing operation.  Boring and honing four cylinders in a bare, stripped down block with main caps in place would not be that costly.  You could use 0.010", 0.020" or 0.030" oversized pistons.  I highly advise smaller bore resizing (0.010" or 0.020" oversize) if possible. 

These blocks do not have great cylinder wall thickness, and core shift is always a concern.  0.030" is the industry standard for reman shops, though that would be the maximum I'd consider.  This engine's wear and cylinder taper should not require a large oversize.  Of course, a straightforward cylinder head rebuild/"valve job" (3-angle seats and fitted silicon bronze guide inserts) makes sense at this point. 

Then measuring down in the bore 2-1/2", the #'s 2, 3 & 4 measurement increases .001 to 3.879 but # 1 is only 3.876. Once again I wonder if the PO honed and installed new rings on the old pistons which would account for some remaining cross hatch and great compression. I also can't explain why # 4 has 175 psi cranking compression.I'm going to try another gauge once the engine is running again.A bad gauge is the most likely culprit.

Your guess is spot on.  These cylinders were silicon carbide ball brush honed with a drill motor, that's not factory crosshatch.  The piston skirt damage is far more than "wear".  This engine was either run low on oil or grossly overheated—I'd bank on the latter.  The pistons were seizing.  The rod bearing replacement was compensation for the insert bearing damage caused by the piston seizure and drag...The PO or a "shop" did a bandaid hone job on the cylinders.  To do so, the head was removed, but the pistons were not renewed.  They look OEM with severe signs of drag from heat expansion.  This heat usually collapses an aluminum alloy piston.

The bores do seem to net the same results when I measure across them in line with the crank so they do appear to be round.Once again, even after much remeasuring to get consistent numbers, I'd be more confident if I had a true bore gauge if it's the difference of a overbore or just a hone job.

Worth confirming...This would help determine whether you invest in a drill motor hone like the Lisle that Wayne used or sublet the bare block to a machine shop that has a good boring bar and CK-10 Sunnen or equivalent power hone.  If you do hone these cylinders yourself, the aim is minimal removal of material, just enough to true (make round and eliminate excess taper) the cylinders and establish a good crosshatch pattern for ring seating and oil retention.

Then I looked at and measured the pistons.Once again I wished for the proper tool(bigger mic) but had to use my oversized dial calipers instead. I can't find these special tools around here without ordering them.

Measuring these damaged pistons should reveal distortion from the heat and drag.  This engine was severely stressed by expanded pistons dragging on the cylinder walls.

I took 3 measurements on each piston. 1 at the very bottom across the skirts (A). 1 across the middle at the center line of the pin (B) and the last 1/4" below the bottom ring(C).

Measurement A(across skirt) is 3.872 on all 4 pistons.

Measurement B( across middle)  is 3.874 on all four.

Measurement C(just under rings) is 3.870 on #2 & #4 and 3.869 on #! and 3.868 on #3. Not sure what new pistons would measure but this seems a bit undersized as indicated by the rocking type wear and scuff marks.

Probably the source of the knocking wouldn't you think. 

ABSOLUTELY, you're spot on again!  Be aware, though, that Mopar cautions against measuring coated pistons.  These pistons, in the areas that were not scuffed and abrasion damaged, could be undersize due to overheat.  They would be "collapsed" pistons...Concentrate on the cylinder bore sizes and condition.  These pistons are scrap and need to be replaced as a set with new pins and rings.

I've added a few pictures of the worst worn areas including a view of the head.I noticed intake valves on #'s 3 & 4 are darker colored then the others.This is both sides of the # 3 piston which is the worst but the others aren't much better.

The top of the #4 piston(175 psi comp.)  was this clean when I took off the head.

You drove the Jeep for a while, presumably without coolant loss.  I would have the head magnafluxed, anyway.  Check the head and block decks for straightness, too.  This engine may have blown a head gasket, which either led to the overheat or, more likely, was the result of an overheat.  The #4 end of the cylinder head deck looks suspiciously shiny, which may be due to a head gasket leak that "steam cleaned" #4 combustion area and the piston crown.  Check the head for true and warp.  Quality cylinder head reconditioning jobs include decking the head surface.

It may be that I'd been testing for the knock source with the engine running by removing the plug wires on these two cylinders as well as unpluging the injectors just before shutting it down.

If my bore measurements are correct and bores are already honed oversize, I'm most likely looking at a bore job.Would you agree or are slightly oversized pistons available to correct my problem ?

As I noted above, you may be able to find high side pistons and ungapped rings (if necessary) that you can gap/finish yourself.  For rings to seal against the walls, cylinder bores must be "true".  Consider the cost (parts and tools) and time to bring all this into spec with an acceptable parts fit, including piston pin replacement.  Compare the cost of subletting the work.  If subletting, I would minimally have the block hot tanked, bored, honed, new camshaft bearings (unless you install them yourself) plus pin fitting the new pistons to the rods. 

Check rods for alignment and bolt stretch.  The piston skirt drag placed a huge load on the rod(s)!  During piston installation, shops routinely align the rods, resize the rod big ends and recut the bearing tang notches, rebush and finish the rod small ends (when the rod design has a floating pin, which is not like these Jeep rods) and replace the rod bolts and nuts.  Make sure you get a full quote with no surprises later.

In the meantime I'll move onto another project until proper measuring tools arrive.

Good plan.  You now know the cause of the knocking, which was a loose and distorted piston(s) and accompanying wear factors.  You have many new parts to reuse, and that's a plus.  Other than your labor, which we both value, the parts investment to date has been worth it. 

Thanks again: Tenny

Thanks for your thoroughness and effort to troubleshoot, diagnose and share with others, Tenny!

Moses

   

 

[Tenny]

Hello Moses:

Since the bore measurements were over the normal limits probably due to already being honed,I decided to send it to a engine shop that I've had good luck with in the past.

I didn't think I had enough to work with at home to true the bores and still have proper piston clearance and figured it would end up at the engine shop anyways to get it right.

I explained to them what my concerns were after inspecting it and they said they would just hone it if possible but agreed it would most likely have to be bored over(as little as possible).

I asked them to check the crank and I also gave them the head to check and service as needed.It should be a reliable little engine when I get it back.I look forward to putting it back together right this time.

I didn't want to get so involved in this engine but decided cutting corners with my fingers crossed was causing me a lot of work and money.

Sometimes you just have to bite the bullet and spend more money to get a good outcome.I'm hoping when the engine goes back in it will be right at last and someone will get a good Jeep.I've learned a lot about spending some time and money up front when dealing with a used motor that you know nothing about.

I'll report back when when I can get back on this project.

Thanks for all your input and help.

Tenny

[Moses Ludel]

Wise decision, Tenny, ultimately a time saver and more thorough approach...See my comments below...Moses

3 hours ago, Tenny said:

Hello Moses:

Since the bore measurements were over the normal limits probably due to already being honed,I decided to send it to a engine shop that I've had good luck with in the past.

Glad you have a reliable automotive machine shop that you can trust.

I didn't think I had enough to work with at home to true the bores and still have proper piston clearance and figured it would end up at the engine shop anyways to get it right.

Highly likely...Without high side pistons (availability very uncertain), a rebore would be inevitable.  At the shop, minimal reboring makes sense:  0.010" or 0.020" oversize if available, though reman parts suppliers focus on 0.030" kits for "every engine".  These days, most shops do a 0.030" oversize as the first consideration.

I explained to them what my concerns were after inspecting it and they said they would just hone it if possible but agreed it would most likely have to be bored over(as little as possible).

I asked them to check the crank and I also gave them the head to check and service as needed.It should be a reliable little engine when I get it back.I look forward to putting it back together right this time.

Good move on the crankshaft.  Could even be sprung from the piston drag, though that's unlikely with a five-main design and the bearings showing even wear patterns.  I'm a big fan of balancing and match weighting the reciprocating parts (crank/rods/pistons, etc.).  Any engine build can benefit from balancing.

I didn't want to get so involved in this engine but decided cutting corners with my fingers crossed was causing me a lot of work and money.

The exchange has provided members and guests with a practical learning opportunity.  The wish thought or "patch repair" often winds up at the machine shop.  In this case, the damage and patch repair were done by the previous owner.  Without a crystal ball, you did a methodical and thorough process of elimination...I'm still curious about that silicon ball hone job.  Was it above the piston at BDC or did the PO remove the rod/piston before honing?  The work was slipshod, especially leaving a radically damaged piston in the engine.

Sometimes you just have to bite the bullet and spend more money to get a good outcome.I'm hoping when the engine goes back in it will be right at last and someone will get a good Jeep.I've learned a lot about spending some time and money up front when dealing with a used motor that you know nothing about.

I believe the borescope would have helped clarify the previous cylinder "work" and turned up the severe score line from the damaged/seizing piston.  Also, for quick troubleshooting, a simple test for valve timing error is to rock the crankshaft back and forth while observing the distributor's rotor movement with the cap removed.  (Take camshaft and distributor drive gear wear into consideration when performing this test.)  This clarifies chain and sprocket wear and may have hinted about the PO installing a new timing chain set or not.  This was not an important point in the long run, as you upgraded the chain and sprockets, anyway.

Your time spent on the worn camshaft and lifters was insightful and valuable.  You ran the engine briefly with the new cam and lifters; during disassembly, did you lay out the new lifters in order for reassembly?  It's early for a break-in pattern but still a good practice.  If the machine shop decks the block or surfaces the head, use a CompCams gauge to establish correct pushrod lengths when you reassemble the engine.

As for the higher compression at #4 cylinder, it's doubtful that the PO's ball honing did anything to improve compression seal.  There was less carbon in that cylinder and on the piston crown; if anything, compression should have been the same or lower than at the other three cylinders.  The #4 piston rings look original with wear.  At this point, it's not worth speculating why the compression was higher.  However, I generally avoid using a compression gauge and opt for a cylinder leakdown test.  Compression gauges can be inaccurate and erratic for a variety of reasons, I use them strictly for ballpark checks during a spark plug change. 

I'll report back when when I can get back on this project.

Much appreciated...Over time, many Jeep 2.5L four-cylinder owners will benefit from your input and the process you have followed.

Thanks for all your input and help.

Very welcome!...Moses

Tenny