Rob Edwards

Mark-

Apologies for not being clear- the set of eight rod bearings immediately above were taken out of the '91 GT motor that I bought in 2008, which became my stroker motor. Those rod bearings went in the trash.


You can see the typical rod bearings from the junkyard motor I blew up at WSIR in the bottom right of this pic. Little bit wider and a little bit thinner than spec:



One junkyard motor shell vs. a 'normal' used shell:

mark kibort

you have to wonder if shinny or mat finish provides a better film medium for the oil. Ive heard that you want the shinny rotating surface and the mat bearing surface. in these pics, i dont think porsche NA would take 50grit sand paper to take off the coating, as it looks like these bearings has been exposed to

mark kibort

OH my gosh.. what a mess!! uggg

anyway, no prob. I thought you used those and put them back in. was that the other set of bearings that didnt look quite as bad? (customer car .... "cobalt"?)

the rod bearing of the junkyard motor looks ok (edit) ( oh, that was the comparison bearing), that wider bearing the fact that it looks burned, is weird....... another discussion....still curious as to what went wrong there. As i posted you guys were not pushing that hard for the few laps at Willow that day... i was in the 1:33-4 for two full weekends (4 full hours of track time and races) and had no issues. Still wondering if it could have been something else that restricted oil flow back to the pickup.

another discussion .... i know... BUT.. i DONT like that old school early 928 pick up system it also looks too restrictive. pan spacer, old pick up system and then the windage tray, might be too much when there is high g loading... the oil might be able to pool in other places where the "ladle" of the newer pickup works better. maybe that is the reason for my success. after all, we are talking 20 years of racing the stockish 928 to its limit and many hours of high g loading.

btw... why was there a difference in bearing width?????? what is a "wide shell"? what up with all the parts looking burned! that engine might not have been in very good shape at all

ptuomov

I'm not convinced that the 2&6 are in any way special _except_ if the pickup sucks air. Then they are special, because they get more air and they get it earlier than other rod bearings.

mark kibort

my thoughts too..... but i think that is the point, as they would fail first, but most interpret it as look at those bearings first ...I dont know if that means anything.... as they all seem to wear the same based on conditions, until there is a problem, and the 2-6 gets the problem first. maybe looking at them at rebuild time, shows if there has been any close calls and there might be more wear there.

Imo000

Mark,

What do you think makes metal turn blue in an engine?

mark kibort

blue usually means heat.

Rob Edwards

Have you ever heard of a 'wide' 928 rod bearing before? I haven't either, they're all the same size.... This one is wide because it got pounded flatter and wider shortly before the big end of the rod gave out.

The 2/6 crank journal got a little warm too:

mark kibort

we saw some warm crank journal in Scots junkyard motor as well. luckily it locked up the crank rather than exploded like yours. however, the bearings were jacked up, but they didnt get pounded wider.

mark kibort

this is what the bearings should look like on a high mileage car. (pay no attention to the scratches .. its amazing how dinged up they get being stored in a plastic bag)
only one set looks to have a worn (shiny) area the rest , the bearing coating was in tact.
this came off a high mileage 4.7 liter US

hacker-pschorr

Twin Turbo Todd has done that a few times, re-used rod bearings. I remember one engine that had 150k or more miles on them.
If they spec out OK, he puts them right back in.

Now, that being said, people need to remember that in his "day job" he pours his own babbitt and makes bearings for industrial applications. He's more than qualified to inspect an automotive bearing for re-use.

GlenL

I've re-used rod bearings. I don't want to spend $150 on bearings that are new when the old ones don't have many miles on them, look good and are working fine.

I do spurge for the new nuts.

mark kibort

seems like such a small price to pay for engine insurance... i guess in theory, nothing touches on the bearings, but the oil , so it should be ok.
rod nuts??? i just use some lefter over 13 or 14mm loose home depot nuts i have laying around.

Imo000

Every time you replace a good functioning part, you are introducing the chance of a failure. Just because the replacement part is new, doesn't mean it is good. As I said before, 3 different standard sizes can easily create a disaster for the average guy. These bearings are easy to inspect. They are basically a bent piece of metal plate. Inspect the surface, measure the dimensions and that's it.

mark kibort

and you know i subscribe to that philosophy too.. its the reason i dont change the water pump if its working on timing belt changes. ive done that before and had bad pumps even though they are new .
i guess its a judgement call..... but i would think anyone building an engine (and changing rod bearings are probably the most technical part, even if the other parts of an engine are not removed) would do the plastigauge test to make sure the gaps are right