Mako 928

I agree with Dave,Sidehatch. The nuts had to come off before all of the carnage, which would be a good indicator to the cause. It would be interesting to see what the tourque is on the remaining rod nuts.

sidehatch

Just so you know i guessed lol,i dont even know what those parts are and if you offered me 10k to tell you, i would loose. Im screwed too, i put thousands in my car and i think shes ready to blow up.

IcemanG17

This would be a GREAT test.....if the others are stupid loose.....theres a HUGE factor in the problem!!

Tom. M

So..which came first..spun rod bearing ..? or backed off rod nuts?..From what I remember...Tom never got into the engine other than routine service and had driven it for at least 5 years..his only real problem being oil consumption.

Maybe the spun bearing heated it up, started hammering, and rod nuts backed off. Or perhaps excessive detonation backed off the rod nuts..and the bearing let go?

Wonder if you can ever find out ?

S4ordie

Looking at the original carnage pics of the bearing and nuts, the nuts looked stretched, which to me seems like they were pulled off the bolt. Flat threads on one of the bolts might be the confirmation.

I am no expert at post mortem engine forensics, but I did stay at a Holiday Inn Express once.

dr bob

I'm thinking you probably don't want to reuse those nuts. Even if you chase the threads, you'll never get the outsides right for a good fit in the crescent wrench. Just sayin'...

Rob Edwards

The nuts are somewhat less than round secondary to their being launched into who knows what after coming off the rod bolts. The threads inside the nuts are strikingly intact and not rolled over. The threads on the rod bolts that you can see are focally flattened a bit but I would think the rod bolt threads would be LOT flatter than they are if the nuts were hammered off over the threads. But then I went into biology instead of engineering 'cause I couldn't hack the math. What do I know?

EDIT: I took a look at some of the rod bearing shells to check the dates on them and most (including those from rod #6) are date stamped 6/85, which suggests that (most likely) none of the rod bearings were ever changed since the engine was new. Curious that they had 7 year old stocks of bearings when building these GTS's.....

Bill51sdr

I've seen this kind of thing happen before on another engine. Not sure about the history of your (late) engine, but I have a feeling that at least the pan has been off and some if not all of the rod bearing caps were removed/reinstalled. What I think could have happened here is that the bearing cap in question here was not seated properly, possibly one side binding on the stud, on the journal when it was installed and was torqued down that way. Once the engine was run a while, both nuts worked their way loose, loosening the bearing cap & voila, you have Rob on the side of the freeway with a perforated oil pan.

Rob Edwards

Greg did some post-mortem (and I do mean post-mortem, now...) measurements on the crank today:

And I quote:

RyanPerrella

and its probably not very cheap to do all that on top of it.

Bummer Rob

are there any new thoughts as to what actually happened? Do you think its just that the track sessions wore out the bearing and it eventually just gave way on your drive?

Rob Edwards

Ryan-

I think that someone at some point R&R'ed the rod bearings on 2 & 6 and didn't get them torqued properly. That is just my conjecture, and I could certainly be wrong, I'm no engineer, and my expertise in failure analysis is limited to dead bodies Doesn't matter, I've already stuck my fork in that motor and am movin' on, as they say. The reciprocating assembly for the stroker is getting balanced this week and the shortblock starts to go together in about 2 weeks.

86'928S MeteorGrey

That's a real bummer on that GTS engine...What are you going to do with it now?

Rob Edwards

Hold on to it for a couple of years (decades?) until I'm convinced that the Porsche 928GTS collector market will never value a repainted, high mileage 5-speed GTS enough to warrant doing some outrageous repairs on this block to keep the car 'numbers matching' ?

It'll never make sense to fix the block, the crank, find 3 GTS pistons, replacement rods, and a complete rebuild on top of all that just to have a 'repaired' motor that I'd never trust to drive in anger. So I guess I've got a bunch of decent spare heads and parts. Much of the ancillary bits from the GTS (A/C comp, air pump, alt, PS pump, Hall sensor, MAF, air cleaner, TPS, CPS) are going to become part of the stroker. And Greg welded the hole in the GTS' oil pan so it could go on the stroker, just to have a little more GTS DNA in there....


RE: the crank, Greg did allow that the crank could be turned down to fit custom Chevy sized rods, and then cross drilled, but it'd be expensive.....

jcorenman

Yeah, but then you would have to use something besides Porsche rod bearings ...

Rob Edwards

One area to add to your PPI list- the rear floor under the mats. If there are rollbar holes and a seatbelt anchor, you might wonder how much time the oil in that car's motor spent suspended against the sides of the sump....