SteveG

Dave: Not questioning you, well I guess I am, but how can you be sure all the teeth in the belt are present and accounted for from the holes in the covers? This thread is long, but the recent post indicates the covers are in place? On my '85, I can't see anything but the top of the cam.

Big Dave

All I can see is that the belt appears to not be shredded, and that everything the belt is attached to moved when the crank was moved (albeit only a short distance).

It's not rule out, except to say that the belt isn't snapped or shredded. We don't know if it has jumped or anything like that yet.

SteveG

Dave: the reason I asked about seeing teeth of the belt, IIRC Jim said that many of the belts die by losing teeth, not shredding. It was an age thing and they became brittle, not miles and I'm thinking if this is the cause, you won't be able to see it from the vent holes, of course the timing marks will be off, but you aren't able to move it enough to see them either? Good luck.

Gretch

Irrespective of the above TB debate, The symptoms are: metal fileings in the oil, engine locked up, (even after pulling the plugs), fuel smell in the oil pan, torque tube done about a year ago, T belt "looks" ok, timing drive train moving with crank movement (very limited crank movement).

Diagnosis is TBF, and the bad news is that there is no cure.



Question for the archives: With a TBF, can the crank offset enough to canter the pistons (and thus the rings) allowing considerably more blow-by and thus the fuel dump into the crank case? The "fuel in the oil" symptome is what threw me off, that and I was under the impression the ailing 928 was a 5 speed.

Lizard928

sterling, it is possible for the teeth to become sheared off the belt due to excessive for and then cause it to skip,

although Dave, take the other persons suggestion and use rubber mallet to "drive the crank toward the rear of the engine, however before this is done, I would recommend loosing the pinch bolt, after the carnk has been move back abit try to crank the engine over, if it turns now then you know it is the TBF and that the crank is catching on a section of the cradle and the engine needs to be replaced.

WallyP

The most common mode for timing belt failure is stripping of several teeth at the crank sprocket. This usually stops the belt and cams, resulting in bent valves. Usually, the engine will still turn over - i.e., it isn't locked down - because the inertia and power of the crank assembly bends the valves out of the way. It would only take two turns to bend the interfering valves, and after that, the crank would turn.

If it is Thrust Bearing Failure, I would expect that if you loosen the driveshaft pinch bolt and release the forward pressure, then push the crank back into place, the crank could then be turned. This might give you a way to check before you had to drop the pan or pull the engine.

Gretch

Well Dave, with Wally suggesting it, that is three of us who propose you push the crank back into place and then see if the engine unlocks.............

Do it. We are all waiting to hear the results. I guess I hope it is something else, but it sure sounds bad. Bummer man.

Jim bailey - 928 International

Pull the engine , oil which looks "cloudy" like metal flake paint is literally metal flakes of aluminium in suspension as the crank shaft throw machines it's way into the engine block . The odds are the engine is beyond repair . IF the drive shaft coupler flexplate clamp bolt was loosened and preload removed the engine just might run for a little while ......more than one 928 with TBF has been traded in to a dealer . One of my customers drove about 400 miles after having his engine seized (TBF) just long enough to get it home after I told him what to do ...... he rebuilt another engine for replacement . Interestingly enough he had bought the car as a engine fire damaged and repaired everything only to discover that it had Thrust bearing Failure ....makes me wonder WHY it burned in the first place !!! Some people when faced with unexpected major repairs opt to " sell the car to their insurance company" .

Big Dave

My thanks to Tony for this image on his site.


I'll get with Rob and crawl under to remove the flywheel cover. I assume that I need to loosen the hex-shaped bolt, and that doing so will cause the flex plate to move, along with the collar, aft toward the rear of the car. I also assume that if there has been a TBF, once the pressure is released, the engine should be able to turn. Correct?

Jim bailey - 928 International

correct on both counts

Lizard928

some good pics here http://home.planet.nl/~Jennit/Techni...ingFailure.htm



For info
http://members.rennlist.com/pirtle/z...ng_failure.txt
http://members.rennlist.com/pirtle/z...ng_explain.txt
http://members.rennlist.com/pirtle/z...g_failure2.txt
http://members.rennlist.com/pirtle/z...g_thoughts.txt
http://members.rennlist.com/pirtle/z...te_loctite.txt

Big Dave

I just talked to Rob. Hopefully we'll be checking for TBF this weekend and I'll let you know what we find. Rob's already looking into options for a replacement engine, including the $2,000 one Mark Anderson has for sale that was salvaged from a car fire.

A local wrench is offering to sell him an S4 engine with 60K miles on it with a 1 year guarantee, quoting him approx $1,600 for labor. I've told Rob that if he does need another engine, he ought to tackle a few other projects while he's at it, including a new gasket set and motor mounts.

One other thing I remember Rob telling me is that at his last oil change they put about 9 quarts in, but that only 4-5 quarts came out when they drained it. Does this support the TBF theory like I think it does?

Gretch

It does dave, if the oil leaked out of the damaged bearing, but there should have been oil all over the back of the engine and the belly pan.

Without looking at the bearing it is not possible to determine if the block is not salvagable. The next step needs to be the crank case inspection.

Good luck to Rob.

Jim bailey - 928 International

Gretch ...No one makes oversized O D main bearings for the 928 so the inability to overbore limits the repair options ....

Gretch

Yeah I appreciate that Jim, and you know vastly more about it than I do. What we don't know about Rob's engine is exactly how much damage has been done to the block. and where One can imagine that for the crank to move far enough forward to be precluded from turning, there may be considerable damage to the rear main bore. However if it is the side of the bore (ie thrust bearing surface) that is damaged, but the bore itself is not damaged, the potential for repair is still there is it not?

In looking at Sterlings deck job, I was very impressed with what can be done with aluminum welding on these blocks. This is what makes me think that if the main bore is not hurt, material can be added to the thrust bearing surface area and machined such that a stock rear main bearing will fit the repaired block. I am trying to learn here, not teach. Share some of what you know aboout this Jim, I am really interested.