Engine Repair "Spun Roller Lifter " GM engines
Middletown NY -
Some engines with roller lifters are using a design of lifter location or retainer that keeps the lifter roller aligned with the camshaft. These plastic retainers have been known to fail due to stresses and temperature causing a noise in the engine. If the engine is stopped in time, it may be temporarily repairable or the system may be restored for long life.
Once any mechanical device is worn - it will never be new again. Nothing will grow metal back on to old parts. Lets get that out of the way. You cant "will" or "pray" things to be like new again unless you replace the entire old system. But we can repair the broken part and get it to function to varying degrees in some cases.
As seen here is a GM engine with a lifter that spun in its retainer causing damage to the lifter and cam. Its possible the cam can be used for some time, but its already worn from the spun lifter, however its possible the owner can choose to try as there are examples of lucky people who drove many miles after similar circumstances. While we suggest to properly repair or restore the system as sound advice, some people just cant afford it. GM has even replaced only the lifter and guide under warranty for noises and spins like this. However a proper restoration would be to replace the camshaft per the factory procedures, it makes sense - the cam lobe is worn and it will not perform as designed.
Now in this case, a unlicensed mechanic worked on the engine before us, and they decided to save too much money by being cheap and re-used the head bolts and many other parts. Had they known what the factory book and training explains - these new engines have bolts that can only be used once - the TTY bolts are one use and trash if you even loosen them. As seen below, this head gasket was already leaking in just 6 days of after the other shop worked on it, causing misfire codes, and the lifter spun again because they did not replace the plastic retention assembly, causing more damage to camshaft. The owner received no utility for the exchange.
Head gasket failed because the TTY head bolts were not replaced. Note the burn marks from poor clamping pressure.
Here is a brand new active lifter and guide installed. The only thing that keeps the lifter aligned is a small plastic tab about .125" of an inch tall. The plastic appears to deform from heat, its important to maintain cooling systems and use a quality oil.
cleaned and oiled cylinders and mating surfaces.
rotated cam to see the wear all the way around. Some galling in center, no apparent effects to lift height, it should be replaced IMPO. However it may run for a time.
Why TTY bolts? Torque To Yield offers a better opportunity for accurate clamping forces, here is why: from an article
When tightening a bolt, overcoming the friction at the threads causes torsional stresses through the bolt (the top twists more than the bottom) and so only the axial stress (tensile) of the bolt applies a clamping force. This is normally in the region of 2/3 axial stress and 1/3 torsional stress.
A TTY fastener is actually employed because, once in its plastic region of deformation, its stiffness/Young's modulus is much lower, raising the ratio of the compressed parts stiffness to the fastener stiffness. This results in the fastener seeing only a very small increase in force when load is applied such as combustion force on a head or inertia force of a con-rod and piston.
Also on a cylinder head bolt, when the gasket relaxes over time, being in the plastic region of the fastener means that a slight reduction of its stretched length due to gasket relaxation means only a very small drop in clamping force compared to what the drop would be if it was in its elastic region.
The type of metal in these bolts is slightly elastic and pulls under varying temperature conditions, this keeps them "tight". But once used they loose their elasticity and fail to "pull" again.
These two issues caused this job to go bad. The tool to properly perform the bolt tightening sequence properly is very expensive, plus the bolts, training, knowledge and experience. Its simply a job for an experienced shop. But in the end, taking a chance by not properly restoring a system is a roll of the dice, and that's a decision the vehicle owner needs to think on, we always advise based upon MAP and manufacturers engineering, sometimes saving a buck costs you more. On this particular issue, the engine ran, but will still make noise due to the cam wear. It really should be done as a complete restoration, but the cam adds significantly more cost. We felt badly for the customer in this situation and tried to save them because of the situation they were already in, but we should have turned the job down - it just is not the outcome we prefer. This engine has other lifters making noise, however the cylinders we repaired are no longer misfiring.
Power is much better, after a 50 mile test drive a side issue appears resolved as well, the customer stated the trans shifts very harshly or hard into 2nd gear, a common issue with these trans, often it is a variety of problems that can cause this, we can fix all of them in the trans but one thing that comes up again and again - if the engine does not run right other things might be affected! In this case the 2nd gear slam was gone after eliminating the misfires on cylinder #4 due to the lifter failure. This engine had counts of up to 10 misfires per 100 , not enough to code yet, on other cylinders, plus noise from other lifters. It also shows signs of a lack of maintenance - this confounds diagnosis - your tech is wading through many issues that could have sequela. The spark plugs? Some old and one new? That's the way it came in,,, it should be tuned up. When it comes to focusing on diagnosis this is the finite item we are discussing here.
Based upon further comments from other dealers and shops it is suggested to replace all the lifters guides and cam as an assembly in addition to the AFM VLOM - others suggest these systems have experienced high failures shortly after one component fails, the labor to replace one component is costly, the entire job is costly, but doing this type of work in small increments will be more costly. Its a difficult decision, we realize that. Think about it, if one lifter has failed, its likely another will be close behind, if the lifter fails the cam can be damaged, and another issue will occur soon. Ugh.... But experience from others seems to show there is much risk with these GM active fuel management 4,6,8 engines.
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