Dissecting 944S lifters

[cjpacitto]

I did all kinds of research and couldn't find any real good info on these lifters.

I am rebuilding my engine and most of my lifters were physically worn. Since I needed to replace most of them anyway, I figured I should dissect a few to try to learn something about them. Here are the pics...

Here is the basic design... a piston which is pressurized by an oil filled chamber. There is only 1 oil inlet hole.


Another picture of the same thing, but you can see the oil check valve (spring loaded ball bearing) in the pistion.


This is how the piston comes apart. Strangely enough, the "piston" is actually comprised of 2 halves that slide into each other (yet another piston/cylinder arrangement). The tiny spring holds the ball bearing in place in the orifice and the little hat clips into the upper half of the piston to secure the spring & ball in place. The large spring works to keep the piston expanded. There is actually another little clip which is not shown in this picture that holds the 2 halves of the piston assembly together (this clip is visibile in the previous 2 pictures)


Here is another view of the piston assembly. You can see the hole in the upper half where the ball bearing goes. (the damage you can see was caused by me cutting the lifter casing open)


Here is a cutaway showing the piston's position inside the casing. The upper part of the piston is always in contact with the top of the casing.


Before I go any further I guess I should make note that these are INA aftermarket lifters. I do not know if the orignal lifters used the same design or not. My head had been rebuilt once already due to a broken timing belt. Most of the valves and all of the lifters were replaced at that time. This was done by a previous owner and I do not know how long ago it happened.


Now when I was originally trying to evaluate my lifters I noted 3 distinct behaviors:

Group 1 has a "springy" feel. I could easily push the piston in by hand and it would spring right back out.

Group 2 had pistons that could not be moved by hand. When I put them in the vice I could force the piston to compress. When I removed it from the vice the piston would pop back out and I could still not move it by hand. (I do not believe it came back out all the way to its original position but it did come back out. I did not run numerous cycles on this to determine if the behavior would eventually change).

Group 3 had pistons that would not move by hand. When I put them in the vice they compressed pretty easily and did not rebound at all.

As I said above, I purchased 16 new lifters (aftermarket Meyle brand for VW 034 engines) which have been shown to be a direct fit for the 944S engine. Of these 16 new lifters, about 10 of them behaved like Group 2 and the other 6 behaved like group 1. From the information I can gather, this is not unusual. The Group 1 lifters need to be exposed to high sustained oil pressure so they can "pump up". The Group 2 lifters are already pumped up.

I actually cut open 3 different lifters for this investigation. One was from Group 1 and the other two were from Group 3.

While dissecting the Group 3 lifters I discovered that the primary reason they were not functioning correctly is that the main piston assembly was binding in the bore of the casing. When I took them apart I found both springs to be in place and they seemed to have plenty of tension. Well, actually, the large spring had plenty of tension... The tiny spring for the ball bearing is so small it had almost no tension in any of the lifters I cut open. None of the lifters appeared to have any "gunk" inside that could be preventing the proper operation of the ball bearing check valve.

I really do not know what caused the Group 3 pistons to stick in the lifter casings. In the absence of any dirt or gunk, my only thought is that it may have been caused by excessive heat in the engine. This engine had been running hot due to an obstruction (extra o-ring) in an oil passage left there by whoever did the first head job. This seems reasonable except that there are many reports of premature failure of these INA lifters on engines without reported temperature issues.

I think that's about it. Just wanted to share my experience in hopes it may help others.

[mallard ducks]

love the "dissection" ... thanks!

[guru944]

Great job and footage.

We 16v Guy's need this kind of info for Tech and troubleshooting.

Later...

[John_AZ]

cjpacitto,

Excellent closeup pictures and lighting.

I like the division of groups.

Group 1 would be the "normal" feel for the used lifter that is not left "pumped up" by the engine. Your explanation is similiar to Bennington Motorsports--
Bennington Motorsports

Group 2 is what I have always wondered about.
They are fine, reuseable. The lifters are in a "pumped up" stage. The piston rebounds after being pressed by the vice.

Group three is not useable because the piston cannot rebound and the cause is uncertain.

Excellent work on cutting them apart.

John