Softer engine bearings

[hardingfv32-1]

My engine bearing supplier/vw rebuilder says that the current bearings available for the 1200 are softer than in years past. He has seen some early failures, particularly the rear main. I personally lost a rear main while starting an engine. It was a fresh rebuild that had been tested on the dyno and properly primed in the car.

Any other people seeing anything abnormal with engine bearings?

Brian

[Dietmar]

Brian:

I only use Kolbenschmitt and have not had any problems- have heard however that this might be an issue with Mahles'

Much as I know
Dietmar

[SR Racing]

We did see one failure. We normally use KSchmidt, but not all sizes have been available. It was similar to what you described. Several warm up runs on the dyno, then 3 or 4 full pulls. Looked great. Shipped it and the customer says it was locked up as soon as they started it. We got it back and found perfect end play (bearing was locked but shims were free.) I don't remember what bearings were in it but it may have been Mahles since we have to use them once in awhile. But after rebuild and dyno runs and a couple races it is fine. (Although that is the only one we have seen fail for a long time. So I don't have any good statistics.)
BTW, the other bearings all looked great. We suspected some crap in the gap some how caused the failure.

Jim

[brian]

The major reason for rear main bearing failure is an out of round case. A one thousandth out of round variance equals 40% of the clearance! If the case is out of round and one puts a round bearing in, the bearing is crushed beyond the allowable clearance. When the crank floats around at high RPM all it takes is one contact with the bearing and poof. Always mic the rear main bore with the cases torqued. If you can feel a lip in the case, right in the center of the bore where the oil passage in the bearing is, then it's time for a line bore or new cases.

Bearing makers have increased the use of aluminum for inbedibility since lead is a no no. VW bearings used to have steel inserts in the middle main but most have all aluminum bearings now. Think about it, you could use baby diapers for bearings if the crank never touches. But stuff happens, thats why NASCAR uses all those expensive coatings.

[smsazzy]

I lost a main bearing on a test day over labor day at HPT. Not sure exactly what happened, but it had plenty of oil and the temps were fine when it happened. Needed a rebuild anyway..... Changing the engine in 105 degree heat was a real peach too.

In fact, Brian, Derek helped me - remember.

Tell your son thanks. It was good to have some help.

[Dietmar]

Only problems that I have seen on the main bearing is that someone missed the locating hole and pinched the bearing .
I did it once and fortunately caught it before completing the engine assembly after it was torqued. Still turned but something was not quite right.

Steel backing on the mains can still be found on the K/S bearings, and the only ones that I have difficulty finding are the (+40 -10) size.

Dietmar

[sharplikestump]

Have had no such problems (knock on wood), but I agree with Brian on the issue of the importance of the bores needing to be round. The other thing to look for while you have that case torqued together is if there is a gap that has opened up above or below the #2 main bore. An excessively hot running engine will cause this. Because of the vast difference in the coefficient of thermal expansion between the case alloy and the 6 steel studs the hold the case halves together, at high running temps (around 260Fand above), torques skyrocket and the grain structure of the alloy is compressed, and upon cooling, a gap opens. This gap becomes an oil galley that you really don't want, as it causes a pressure drop. At the same time, the web that forms the saddle for the #2 main typically shifts, one side up and the other down, along with the center cam bore dropping out of concentricity with the other two. The center of the case has actually become taller and narrower. All bad.
Once a case has shifted, even with re-boring, there can be problems. I have seen where such a case can test just fine on the dyno, but when pressed on the track and being subjected to the higher temps (especially in a prolonged draft), the alloy decides to return to it's former location. This exerts excessive pressure on the bearings, which in turn creates more heat, and also causes the power to fall off after a few laps.
Obviously, modern syn. oils can handle much higher temps, but our cases can't.
On the subject of steel vs. alloy #2 mains....i have seen the alloy ones actually shatter, and this was stock engines! I usually maintain a supply of 80 to 100 sets of mains (hate running out when I am building one at midnite), and I just checked my latest batch ordered...all steel (whew).
Dietmar: If you get in a bind, I have 6 sets of those on the shelf.
Mike

[FV55inSpokane]

Like Mike was saying the center main webs can actually change shape from an over heating condition. An easy way to tell if this has happened is to look at the vertical web surfaces when the case is in half. If they look shiney or polished then it's time to scrap the case....as far as I know anyway. If you look at the ends of the two bearing halves you can see where they have been mashed together and usually have some scaring on them from the pressure.
Lawrence