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Moses Ludel

Jeep 232, 258 and 4.0L Inline Six-Cylinder and 2.5L Valvetrain Noise and Valve Adjustment

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Many Jeep owners need how-to information on checking valve clearances and adjusting the hydraulic valve lifters on the inline 232, 258 and 4.0L six-cylinder engines and the 2.5L Jeep pushrod engine.  Between the model years 1971 and 2006, Jeep used these AMC-design 232, 258 and 4.0L sixes and the 2.5L straight four-cylinder engine (1983.5-2002).  The hydraulic lifter and valvetrain design has particular needs, especially the valve clearances.

  

 

When these engines develop valvetrain noise, owners often think a valve adjustment will cure the problem.  In each of these AMC/Jeep engines, valve clearances are set during assembly of the engine, and adjustment is not necessary between engine rebuilds.   If your engine has developed valvetrain noise, or if you are in the process of rebuilding the engine and need to know more about setting valve clearances, my HD video from 4WD Mechanix Video Network at Vimeo will assist.

 

This video was originally a Q&A Vlog at the magazine, now available for a broader viewing audience through Vimeo.

 

Moses
 

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Good info, thanks.  Here's an odd one I have been trying to figure out for years.  I bought the Jeep at 57,000 miles ('97 TJ w/ a 2.5L), and now it has about 200,000.  So I am assuming now it's worn out and am just going to swap it out.  But, this is what it has done for years:

 

First cold start of the day, it is quiet.  After about 30 seconds or a minute of warming up, I can hear a valve clatter/tapping noise starting.  It did this until the engine was up to temp, then would go away as long as the engine stayed running.  If it sat for a while and cooled off, it would do it again until warmed up.  This never impacted the engine's performance or drive ability, so I never really worried about it.  

 

But, in the last year of driving it, the noise would appear at about 30 seconds or 1 minute of run time, but would stay once the engine warmed up.  It would be quieter once warm, but definitely audible.  It almost sounds like a diesel.  

 

This Jeep has sat now for about a year and a half, but I am going to revive it this winter, as well as do another build on it.  Also plan to swap the engine for something else, but will always be curious as to what was making this noise.  When I have a chance, I am going to tear the engine down and see if that shows anything.  

 

It definitely doesn't sound like a rod knock, and is coming from the upper part of the engine.  So I am assuming it is something in the valvetrain.

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Two possibilities here, Mike.  Like you suggest, it could be sluggish oil flow through the hydraulic lifters, the lifters bleeding down, or possibly excess valve/lifter clearance from valvetrain wear.  At 200K miles, that's a very real possibility.  Another possibility, since you're certain it's not a lower end bearing noise, is a carbon buildup knock (not likely with an MPI engine) or a piston-to-wall clearance issue.  Piston skirt wear is likely, too.

 

It works like this: Pistons naturally expand from heat.  There is the normal piston-to-wall clearance to accommodate expansion when new.  Over time, the cylinder bore wear creates cylinder "taper" toward the top of the cylinder.  The piston skirts also wear.  Over time, the cylinders and pistons wear. 

 

Cold, the engine was noisy, the pistons expanded, and for a while, anyway, the engine quieted down when warm.  Now, the lifters are clacking, the cylinders are worn, the pistons have worn, and you get the sound effects! 

 

Another noise can be piston pin wear, which causes a double-knock rap...You would notice this clearly as a dominant sound when the engine is unloaded and you tip the throttle in and out.  Use of an automotive stethoscope, a copper tube or a piece of PVC tubing can help isolate engine noise.  Be aware that these noises will be transmitted widely and very exaggerated while using these sounding probes!

 

At 200K miles, your 2.5L MPI engine is a testimonial.  It has done a heroic job tugging a Jeep TJ Wrangler around for this many miles, likely with 4.10:1 axle gears, which make the piston travel extreme over this many miles and wear an engine out sooner.  You should either provide this engine with a suitable burial or rebuild it completely, restoring the short block and cylinder head to OEM specifications. 

 

An inline 4.0L six swap is not that easy, I'd consider a small V-8 swap as a practical alternative.  The Jeep YJ and TJ Wrangler frames are, for unfathomable reasons, designed specifically for either an inline four or a six-cylinder inline engine.  (You can see photos of the motor mounts I fabricated during a 4.0L swap into a 2.5L YJ Wrangler, and frankly, it would have been just as easy to install a hybrid V-8.)  Granted, the 4.0L radiator, shroud and transmission locations were straightforward, although your four-cylinder model uses an AX5 transmission, which would be replaced by a 4.0L's AX15 transmission.  Aside from fabricating motor mounts, there would be wiring, cooling, exhaust, the AX15 transmission, 4.0L PCM setup and other changes.

 

Keep us posted on your plans for the Jeep TJ Wrangler.  We're here with comments and suggestions on what alternatives you might take here.  You can do anything from selling the four-cylinder model and replacing it with an inline six model to engine swaps or simply rebuilding your existing 2.5L four to get another run at 200K miles!

 

Moses

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Thanks for the detailed and quick reply Moses, very interesting tech.  I think you're right it is probably multiple worn parts making clattering together.  I am looking forward to tearing down this engine one day and seeing how it looks/checking the wear.  This is Mike at MCE Fenders (MCE Mike on Facebook) and this is the lime green Jeep in our photos.  (Also emerald green before it was painted) I've owned this Jeep since I was 16 in 2000.  

 

You are absolutely right, this is a testimonial for this engine.  I am absolutely amazed at how problem free and durable this engine is.  Since it doesn't have much power, and had larger than stock tires on it since ~60,000 miles, this engine spent a lot of time at full throttle and/or high RPM.  It has had 31s and 4.10s for a few years, 33s and 4.10s for about 6 months, 33s and 4.88s for a few years, and has been on 35s with 4.88s since 2008.  I could also go on about all the times it spent revving high in the snow, breathing dust in the Moab and PNW silt, and it has overheated a few times due to a water pump and electric fan issue.  I always just kept the oil changed.    

 

I am probably not going to do an engine swap for a while - just not enough time right now and focusing on other Jeeps and the company, but am collecting ideas on what to do.  I am definitely leaning towards a small V8.  I don't want a huge powerhouse, I rather have reliability of the entire Jeep rather than a HP number on paper.  So was thinking a Vortec 4.8 or possibly a 5.3.  From the research I have done, the Magnum 5.2 and 5.9 are the "easiest" swaps for my TJ electrically, so those are also on the drawing board.  

One other idea is to try 505 Performance's new 2.5L stroker kit and head.  (2.7 and 2.9 options)  But I am still researching this.  While the sound and power of a V8 is fun, keeping the light 4 banger but adding power might also be fun.  

In '08 I swapped the AX-5 for an NV3550 with junkyard parts, and bolted on a NV241-J to that.  So I am thinking they will be fine with either option.  The front axle is a high pinion 30 out of a Cherokee.  This would probably be fine for the stroker 4 cyl. option, but probably need replacing for the V8.  This Jeep doesn't have a rear axle at the moment, but it will probably get a D44 when I have time to get to this project.  

Too many options, haha!  


Mike  

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"Jeep'd out" at the moment, eh, Mike!  Each of the options you describe has its merits.  I'd likely do a 5.3L V-8 and plan to go lighter on the throttle.  This would pull the tires and current gearing well, and the NV3550 would hold up with a stock 5.3L; the NV3550 is close to the stamina of an AX15.  Our fellow forum member spdljohn has an LS 6.0L with 325 horsepower coupled to a fresh AX15.  Driven right, the NV3550 will hold up.  The NV4500 would be an explosion-proof alternative.

 

Like that 241-J transfer case, too.  V-8 material...A D44 at the rear would suffice, even the D30 at the front would hold up with the 35s and 4.88 gearing.  The front axle is only engaged with the rear pushing, the torque split is 50/50, the D30 gets only half the load placed on the D44 in 2WD mode.  A D30 under this arrangement can hold up, though many opt for a 44.  The TJ Rubicon type front axle is available readily, though it uses the lighter axle tubes.  The gain is ring-and-pinion size.

 

I'm a turbo diesel guy.  The Isuzu four-cylinder Iveco/GMC diesel still has my attention.  I had a tentative swap planned for the XJ Cherokee, our friends at Advance Adapters were fully supportive.  Unfortunately, since 2009 California will not recognize this kind of swap.  The Isuzu diesel is only used in medium-duty trucks.  The Cherokee is passenger car/light truck emissions.  I could "legally" do this swap at my rural Nevada county but preferred to do a 50-State legal swap. 

 

Perhaps the medium-duty Isuzu four will turn up in someone's 1/2-ton pickup soon, as it is emissions friendly.  The 3.0L Jeep/Ram 1500 V-6 diesel is still too new for ready access, and the cost of a swap engine would be prohibitive.  I avoid unaffordable swaps, a disservice to the 4x4 community.  Until this 3.0L V-6 becomes a Mopar Performance "crate motor", I'll avoid that engine for now.

 

Have a great New Year, Mike...

 

Moses

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4BD - nice option also that would probably get good fuel mileage.  I will have to start another engine swap thread so this one stays on topic about valvetrain and doesn't get cluttered with swap ideas.  haha

Happy New Year to you too Moses, thanks for the great tech,  


Mike

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Hi guys, great to have found this forum. 

I have an Israeli built ,cj6 in Sinai Egypt where I live part time. It’s a 78 two barrel, I’ve never known if it’s a 232 or 258. Just recently I’ve had problems with cylinders not working, it’s not the carb or electrical.

twice , a pushrod has come out from under the Rocker, causing backfiring through the carb. I didn’t realise the tappets were hydraulic and could not understand how this had happened.

A mechanic, (we are talking dessert here ,third world facilities and non existent tools, well maybe a hammer and odd spanner’s) tried to sort it but said I needed new lifters. Which are unavailable.

So im researching this stuff , and have ordered parts from rock auto which are coming to England. Next time I’m out I will rebuild the head , and put in the new lifters.

I get the bit about , slightly depressing the lifter at TDC. But where does this leave the gap ( or non ) between the Rocker and valve. Should there be any clearance or should this be tight, though obviously not opening the valve.

i read on one post that you can shim the Rocker bridges,( some are with bits of coke can) or even file down the fulcrum bases to compensate for any difference.

im sure there must be other posts , if somebody could highlight them please.

lastly Mosses ,  if you are still on the site I’ve got your book in Egypt , a great read and thanks for the video.???.

 

D68904D9-75A5-465C-A403-66EE429E1C15.jpeg

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markfitton...I'm still here!  You have a very original looking AMC "export model" CJ-6, unusual by 1978 U.S. standards, though AMC/Jeep did produce a CJ-6 body for the U.S. market through 1975 (prior to the CJ-7 era).  In any case, you likely have a 258 inline six with your 2-barrel carburetion.

So, the valve clearance is "zero" plus an additional depression or "preload" of the hydraulic lifter plunger.  Imagine the lifter plunger in its normal, fully extended position.  Now envision the pushrod taking up the clearance between the rocker arm seat and lifter's pushrod cup.  This would be zero clearance.  Since this is a hydraulic lifter, it requires a lifter plunger preload.  Preload is the depression of lifter's plunger from its fully extended position downward into the lifter.

Your engine's hydraulic lifters need this preload to 1) prevent the plunger from pressing against the retainer clip and popping the lifter plunger loose and 2) to allow for minor valve face and seat wear.  Face and seat wear means that the valve rides higher and tips the rocker further downward, which presses the pushrod further downward.  In actual engine running/operational mode, the lifter oil and check valve hold its plunger height and keeps the valve clearance at a zero-gap position.

This is a great generic illustration courtesy of a G.M. Performance website.  Note the pushrod and "socket" position in the preloaded mode.  The lifter's oil level maintains the zero-clearance between the pushrod and rocker arm.  "Zero" just removes the valve stem-to-rocker arm gap without unseating the valve.  This consistent zero clearance is maintained by the lifter's plunger height, which is controlled by the check valve and oil volume in the lifter's cavity.  Valve spring pressure seats the valve and helps establish the zero gap point: 

Image result for hydraulic lifter diagram

This is why I talk about the use of a pushrod length gauge to measure the zero gap dimension.  Again, you want to bring the piston to TDC on its compression stroke (both valves closed).  At this point, you want to know the measurement between the rocker arm seat and the lifter socket seat with the lifter plunger fully extended to the circlip.  Once you know this length, add the desired additional preload length to the pushrod.  This additional length establishes the correct lifter preload. 

For non-adjustable rocker arm engines, Jeep does not provide a preload specification or pushrod length measurement anywhere in its service literature.  When valves and seats are ground, the valve stem height is crucial.  (Milling or surfacing the head will also alter the valve stem height.  So does installation of a thicker or thinner head gasket.)  Valve stem height affects the lifter preload.  The only way to "adjust" lifter preload is with the correct length pushrod or by grinding off the valve stem tip to establish the correct valve stem height and plunger position in the lifter.

If you want an arbitrary pushrod preload length, most use a figure of 0.020"-0.040" depending upon the lifter manufacturer's recommendation.  This means that the pushrod(s) will press the lifter socket/cup and plunger down this far with the valve closed and camshaft lobe on its heel (lowest point).  When the pushrods fill with oil (do not fill the lifters with oil, let them fill with the engine running), the oil and lifter check valves will hold the lifter plungers at this height in the lifter with the engine running.  The check valve keeps the lifter from bleeding down.

The term "clearance" is misleading in the case of hydraulic lifters.  These lifters create zero (theoretically 0.000") valve stem tip to rocker tip clearance while the lifter plunger rides at a prescribed height within the lifter—a height that we call hydraulic lifter "preload".  Valve "clearance" is the term originally applied to mechanical lifters.  Mechanical lifters require a running clearance or gap between the valve stem tip and rocker arm tip when the valve is closed and the camshaft lobe is on its heel.  This actual gap is set between the rocker arm tip and the valve stem with the piston at TDC on the compression stroke.

Trust this helps clarify...Let us know how the project unfolds.

Moses

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23 hours ago, Moses Ludel said:

position.

Hi Moses, thanks for all that , I will be in touch when I’m next in Egypt , probably May to let you know how I get on.

the jeep is actually an Israeli one, built in Haifa. The body is made of thicker metal than the normal jeep. It’s also sought after in Sinai as it’s regarded as being stronger, Body not the engine. 

I could never work out the engine code or chassis stamp, as they don’t correspond to the American system. There wasn’t a vin plate when I got it either.

i even tried matching it with an Israeli, who had all the factory vins, but he thought it was a latter year, but it could have had an engine change.

originally it had a three speed box with a Dana 20, but I found  a T176 and d30 from Cairo. The local mechanics changed it over,amazing what these guys do to keep these jeeps running. Some time I will get the Novac rebuild kits for these.

you really wouldn’t believe some of the ones running around, the only problem ,if it’s running they don’t think there is a problem. Preventative maintenance and making it run better or restoration is an alien concept.

Thanks very much for your detailed reply, I’m so glad I found the site.

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You're welcome, markfitton...My Mopar Parts manuals are 1981-up, so I can't look up the Export details prior to that year.  (I have books for the Willys-Kaiser era, but that's too early.)  Some telling I.D. numbers on the engine would be the carburetor type and tag or casting numbers, the distributor type and number, and the block and cylinder head casting numbers.  These can provide build time ranges that narrow down the age/model year.  Casting numbers are often very useful for pinpointing engine size and equipment without a teardown.

Please stay active at the forums.  You have a unique vehicle.  The T176 and Dana 30 were definite improvements for both dependability and 4WD use.  The low range crawl ratios are much better with the Dana 300 than a Spicer/Dana 20.

Fun stuff...Enjoy getting some use out of the Jeep CJ-6!

Moses

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