Hydraulic Lifters and Camshaft Lobes Repeatedly Failing

[Chris]

Hello all,

'94 Wrangler with 2.5L, about 170K+ miles ... initially running rough under load followed by loud top end noise.  Found #2 intake lifter had been beaten quite a bit by the cam lobe (which was also now quite worn).  No other wear found in valve train (push rod not bent) and valve not stuck.  Replaced cam and lifters but less than a 100 miles later same lifter is in same condition (contact face noticeably worn from cam lobe and engine running rough under load).  I should also note assembly lube was applied to the bearing surfaces, lobes and lifter faces.  Ran it in at 1500 rpm for 20 minutes.

Oil pressure is good and good oil flow through lifters and push rods.  The only thing I can theorize is the lifter "bearing" (hole in block where lifter sits) is oversize and lifter is "chattering" in the bearing, causing it to stick and get beat up by the cam lobe.  Has anyone else experienced this?

Thanks,

Chris

[Moses Ludel]

Hi, Chris...This has to be frustrating, lots of work involved with the camshaft and lifter change!  Thanks for the details.

I'm guessing that the engine had never been fully rebuilt?  All parts were original when the initial problem began?  If so, I would check the valve rocker arms at #2 cylinder for worn pivots, worn tips and the valve stem alignment with the rockers.  If the rocker arm is binding on the valve stem tip or cocking sideways, this could place an uneven load or angle on the pushrods.  If at a specific valve like #2 intake, I would also check for valve stem and guide wear with possible binding in the valve guide.

This can all be checked without removing the cylinder head.  Bring #2 piston to TDC on its compression stroke to close both valves.  Remove both of these rocker arms, which will fully seat the valves.  Inspect the rocker arms and valve stem tips.  If you would like to check the valve stem/guide wear or for binding, keep the piston in this position and use an over-the-valve (straddling) valve spring compressor to compress these two sets of valve springs.  (Note their positions and valve spring orientations.)  Before removing the springs, stuff rags into adjacent orifices and pushrod holes to prevent dropping a valve lock into the engine!

With the springs compressed, valve locks removed and valve springs removed, you can test the valve stems for radial or sideways movement in their guides.  If there is play, the valve stems could be sloppy and/or binding.  

Caution:  During this work, do not lower the piston; you want to prevent the valves from dropping into the cylinder.

Let's discuss your findings and go from there...

Moses

[Chris]

Hi Moses,

Correct on everything being original.

As luck would have it I had to replace the cylinder head shortly after due to a crack and I can say for sure that none of the valves were stuck or had mushroomed stem tips.  I didn't notice anything odd about the rocker arms or pivot but it might be worth another look.  

As you can imagine, I'm reluctant to replace anything at this point until I can identify a cause.  Some research on the net revealed other folks having issues with flat tappets (apparently the market has given way to rollers and no one wants to make quality flat tappets anymore?)  I'm about ready to swap this engine with a junker just to get it rolling again and then tear this engine apart and mic the lifter bores ... I'm still thinking maybe the bore is too large and the lifter is chattering instead of turning.  

Chris

[Moses Ludel]

Chris...Oiling is critical, you share that the oiling is sufficient.  You replaced both the camshaft and lifters, and that's a mandatory step.  It helps to understand that the lifter contact point with the lobe is the highest pounds per square inch load in an engine:  Up to 230,000 pounds per square inch!  Envision that the lifter base is convex, the lobe surface is flat.  The actual contact point is minuscule, and the only barrier to rapid metal disintegration is the oil film! That's asking a lot of the oil.  

Note: Oil spray on the lobe is essential, not just the oil running through the lifter galley.  Any obstruction to oil spray on the lobe can cause a problem and rapid lobe/lifter wear!  Sludge buildup is common in higher mileage engines that get taxed like a 2.5L AMC/Jeep design four.  I've seen these engines with a dramatic coating of sludge on all of the oil-cooled areas of the block and heads.

Modern break-in of an engine is more a case of establishing the right camshaft to lifter base pattern than concern for piston ring seating, though each is important.  Roller lifters went far to reduce camshaft/lifter break-in needs, flat tappets are the most complex for break-in and setting up a proper interface pattern between the lifter and lobe.  Any resistance in the valvetrain or overly high valve spring pressures can be an issue.

This raises a point about your cylinder head.  It is common practice for shops to shim the valve springs as a cheap alternative to new springs and to compensate for valve seat cutting (which sets the valves further into the head and raises the valve locks point, thus lowering spring pressure).  If this is done arbitrarily, without consideration for actual spring pressures at full rocker opening, the valve spring pressure can be excessive, especially true if the seat cuts are shallow and the shims get used anyway.  Overly high spring pressures, combined with a new camshaft and possibly sub-par lifters provide a recipe for parts failure.  

The fact that the very same lifter and lobe failed, however, points to a problem that existed both before and after the camshaft/lifter change.  You mentioned the possibility of lifter bore wear or binding of the lifter in its bore.  This would also cause misalignment of the lifter with the camshaft.

Another issue can be valve spring bind if the lifter plunger is not at the right height in the lifter.  The lifter plunger must ride at the correct position in the lifter, if it bottoms during the lobe travel, the valve can interfere with the piston or springs can bind.  Too little lifter set and the plunger can actually pop out the lifter's plunger retainer.  Proper lifter clearance is important.  This can dramatically impact the lobe and lifter wear.

Caution:  Do not soak the lifters in oil or "pump them up on the bench" before installation.  Coat the lifter exterior and base with engine assembly lube, the lifter should have a slight coating of oil on internal parts during manufacture.  If "pumped up" to full plunger extension, the lifter will open the valves way too much during initial cranking and possibly bend a valve against the piston.  Not filled with oil, the lifter plunger will center up promptly during cranking.  On a fresh engine, you can pressure prime the oiling system once the lifters and rockers are fully installed, and this will aid lifter fill during initial cranking and starting.

Make sure lifter clearance is correct.  A milled block deck or cylinder head will alter lifter clearance, causing the lifter plunger to ride lower in the lifter.  Valve seat cutting without adjusting valve stem heights or pushrod length will also alter the valve clearance.  Valve spring bind or compressing the springs too much is always a concern.

Moses