GregBBRD

The oil pan was perhaps the cleanest pan I've ever seen, off of one of these engines. No deposits. No darkened color. Perfectly clean inside.

Interestingly enough, the oil pan had a GTS baffle installed, which almost has to mean that someone has been in here, before. The oil pan has the correct date (40/89) date cast in to it, so it is doubtful it ever got replaced.

Fabio421

Greg, why do you say this? Please elaborate. I am about to replace my rod bearings "while I'm in there" and your comments have me second guessing this.

Thanks

danglerb

My uneducated guess is that a bit of debris got in the oil and dug a groove on the way out through the bearing.

soontobered84

LMAO Now THAT is funny......I don't care who you are!

GregBBRD

Obviously, this is always a possibility. However the main bearings have absolutely no trace of any debris...and the oil has to go through there first.

These bearings simply ran out of oil film and were scraping on the crank.

WallyP

I will cheerfully state up front that my expertise is an order of magnitude lower than Greg's, but I am slightly puzzled by the uneven wear patterns. My first suspicion would be that the rod surface wasn't as clean as it should have been, but that is hard to accept on a factory installation.

I just think that contact wear from a perfect crank surface should be more even than that...

gbgastowers

Is there supposed to be any play in the shaft to the drive gear? Gunar

GregBBRD

Great point! I'm so used to seeing contact patterns like this, that I just skim by that detail. I'll look closer and see why this would happen, this way, although I suspect that it has to do with the oiling hole that is drilled into the crankshaft.

One thought...seems like all the bearings have the same wear, which would mean that they all have the same problem, with regards to whatever touches the crank, first.

IcemanG17

Doc
did you mic the bearings? I know its not exactly an accurate measurement, but it would be interesting to see how thick they are?

GregBBRD

Been through this a few times, but here's the highlights.

The bearings are supplied by Porsche in three separate dimension "groups", which vary by about .0002, from size to size. These sizes are blue, yellow, and red...with blue being the "smallest/tightest" bearing. Porsche originally picked rod bearings that were sized to the particular crank...to get the correct oil clearance. The cranks were marked, when they were made with a paint mark and the assembler simply matched up colors. The colors washed off instantly.

Porsche r eplacement bearings are supplied two to a box and they are also marked with a color code, although you can not specify which color you want, any longer. They will always come with two yellows (mid size clearance), or one blue mixed with one red (tightest bearing with biggest bearing...I guess they think this equals two yellows?) You will see no other variations, unless someone has mixed things up, after they were boxed. We go through these bearings, confirm their sizes, and will actually pick sizes to get optimum oil clearance. (We would never put a blue with a red...makes no sense.)

The aftermarket replacement bearings, made by Glyco, don't come supplied with any colors. They generally come very tight. I think they plan on the cranks wearing slightly and intentionally build the bearings tight to compensate for any wear. However, the cranks are very hard and do not seem to wear...so it is very possible to get bearings that are too tight and not provide enough bearing clearance. Many engines have failed, immediately after a bearing change...possibly from this.

There is also some that think the bearings are constructed differently, of which I was one of. However, after weighing many of these bearings to try and compare, they all seem to weigh very very close to each other...which might indicate they are built from the same materials. I simply don't know.

I am currently running a test engine that has a "mixture" of factory rod bearings and Glyco aftermarket bearings, for a study. They were carefully selected to be all sized the same. We will run this engine for 6 months or a year and check the bearings for wear and compare them. There are also several other "developmental" pieces that we will be reviewing, when that "inspection" occurs.

Here's my ideas....measure very carefully and make sure that you have adequate rod bearing clearance. Compare the replacement bearings with the original bearings, for size purposes.

You've got to take this all with a grain of salt, however....I'm not an SAE member....so that magazine has not made me an expert.

soontobered84

That's incredibly funny, too! Greg, you are killing it today. I've been laughing since the first flame.

Daniel Dudley

So is plastigauge sufficient for checking the bearing clearances ? Do you replace the rod Bolts and or nuts ?

RFJ

tho i have little experence with porshe (none to be fair) i have rebuilt many chevy and mopar engines and more often than not there is what looks like damage from , sand or some debrie on the rod bearings and yet the mains look fine, could someone explain or is it bad karma?Ray

GregBBRD

Yes. They somehow "punched though" the oil film and touched the crank....the loads are way higher on the rods than on the mains. once you've torn a small chuck of bearing material loose, it is stuck there and makes a huge groove.

GregBBRD

I've never been able to get Plastigauge to tell me much...I measure things with micrometers.

Always replace the rod nuts. Bolts should last the life of the engine, as long as they don't get overtightened. If you ever need to replace a bolt, the rod will need to be reconditioned (rebuilt).