AO

Working on Rhudy's car today. Popped the bearing caps off on 2-6.

There's a tiny spot of copper at the edge where the bearing halves mate. Thoughts on replacement?

AO

BTW, the one showing the copper spot is the 2 bearing.

Here are a couple pics of the other half of the 2 bearing.

tveltman

Honestly, I would replace it no matter what. I guess I've never tried to rebuild a 928 engine (yet, it's in the cards at some point), so maybe the cost isn't justified, but while I had the thing apart, I'd do them all just to be sure, especially considering what is known about 2/6 failures. Just my 0.02

dr bob

Those should be replaced IMO, and certainly the others should be checked at minimum. Mic' and carefully inspect the crank too. Looks like you might have dodged a bullet.

Landseer

It might be instructive to know if there are any telltales on this one in an oil filter disection.

GregBBRD

The bearing on the right of your upper pictures is fine. Tough to really tell much about the bearings on the left of those two pictures, but it is concerning that there is no longer any "untouched" area near the parting line. This is where the bearings get more eccentric and really shouldn't ever touch the crank.

The two pictures of the upper bearing for #2 show the dirt/loose particle damage from the lack of oil which allowed the bearing to "touch" the crankshaft. I'd replace the bearings in #2, at minimum. Measure them carefully and make sure the replacement bearing is not "tighter" than the existing bearings. You might get a more accurate bearing measurement from the "right" bearing, in the upper pictures.

Imo000

These bearings don't fail becasue of wear. They fail because of lack of lubrication. You can have a brand new set and under the right circumstances, it will fail jsu tlike an old set. Probalby fail a little faster than a slightly loose bearing.

S4ordie

AO, Greg missed one important recommendation that drbob stated..... check all the bearings. As we discovered in the Zyclamrot car the #2 and #6 bearings had similar but less wear than what you show. After some deliberations I instructed Greg to check the remaining bearings. Guess what? The #2 and #6 bearings were in the best shape of the eight.

This evolved 928 SOP of only checking the #2 and #6 bearings because those are the cylinders that fail the most is flawed logic.

AO

Thanks for the responses. We checked the other bearings and while they look okay, we've decided to replace all of them.

GregBBRD

Yes, I didn't bother trying to go down that road.

Rod bearings are "throw away" items in the automotive world....just not in this little 928 world.....hell, there are people here that talk about re-using gaskets. It would have to be a really really perfect rod bearing for me to remove it and re-use it. And there would have to be a damn good reason to not inspect all of them....like Porsche ran out of new rod nuts.

When we dynoed Andy's engine, we ran it pretty hard. There were two "over-rev" situations where the dyno mysteriously "released" all load and the rev limiter tripped and shut things down. Additionally, there was at least one dyno run where the oil pressure dropped, due to a lack of oil in the pan.

After the dyno tuning, I pulled the oil pan and inspected the rod bearings...just to insure that Andy would start with a really fresh engine. There was a bit more wear than I considered "normal" and I rolled in a new set of bearings, remeasured the rod bolt stretch, and put it all back together.

BC

When you say "rolled in" a new set do you mean simply that you lightly lifted (or pushed) the piston and rod assembly up so that you could clean the rod half of the big end and slip in another rod bearing?

GregBBRD

Exactly.

James Bailey

Probably not something you would read in the factory repair manual just shows that years of experience does not come in a book.......or on line

jcorenman

Greg, by "measure" I assume you mean measure the bearing-shell thickness with a ball-micrometer and compare new to old??

Thanks for posting, great info!

123quattro

It's a fairly common trick. I helped change the rod bearing out in a Gen III Supra this way. Start to finish we were done in 2 hours.