jrgordonsenior

Pics of the end of a GT3 Cup Car crankshaft after the flywheel sheared 3 bolts and rattled out the others. We originally thought the pressure plate/clutch had failed as it felt OK, just wouldn't go into gear. Check out the moonscape on the end of the crank from the flywheel rattling around. Unfortunately this will require a new crank and since we're in there.....

dug911

Holy cow give us more details.

How fast were you going and how is the trans?

amondc

Were you running the stock clutch set up? or tilton? I have heard there is a problem with the tiltol flywheels that have diamond shaped holes in them, the later one have a round hole. How many hours were on the motor?

jrgordonsenior

02' motor with 30 hours since complete rebuild. Flywheel is stock though it had a 3-tab pressure plate which I believe was used in 03'-04' cups (4-tab in 05?). The pressure plate was dinged up to match the back of the flywheel, the clutch plate looked fine but they rarely wear out in cups anyway (usually the pp).

The question is what caused the bolts to rattle loose? Loc-tite was not present on the remaining bolts. So..... were the bolts not properly torqued on installation, or did the crank became harmonic for internal reasons and vibrate the bolts out shearing off those last 3. We'll see.....

amondc

Good luck. Let us know if they find out anything as to why it came apart. Will have to double check the bolts next time we have the motor or tranny out.

Chris

Greg Fishman

How many hours were on the flywheel? Long time ago but I remember my mechanic (Brian Copans) said that after around 40 hours they needed to be replaced. Might have been on the RS's though.

Ed Newman

Been there done that on a 600hp boat motor... flywheel w/o loc-tite will soon be flying away

jrgordonsenior

I'll be seeing Brian Copans today and I'll ask him about that....

jrgordonsenior

Split the cases today and found visible uneven wear on main bearings. I was also told today that a batch of 02' flywheels were unbalanced and replaced back in the day. That of course just adds to the list of possibilities.....

So possible causes are out of balance flywheel that vibrated loose, under torqued bolts on the flywheel though I don't belive that would cause uneven wear on the mains, a bent or unbalanced crankshaft, or most likely, a uneven line bore when the motor was rebuilt 30 hours ago.

So we may never know as the cases, being 02's, will be trashed and the motor rebuilt to 05' specs. Did you know that the motor parts for 03'-05's are cheaper than the early cup motor parts? Well me neither until today.....

leif997

whats the cost differential b/w a rebuild to ' 05 specs and a new motor?

jrgordonsenior

We were debating that yesterday at PMS open house. My friend, whose motor this is, is going to call PMS on Monday and find out if they have any 996 cup motors lying around rebuilt or new and at what pricing. New crate motors used to run around $55k. I would think you could improve on that substantially IF you can get the parts.....

leif997

I am pretty sure that crated rebuilt engines from PMNA are substantially less expensive; and with most of the teams going the 997 route this next season, there should be some race teams with "available" inventory to be capitalized upon. My route would be to gain a crated rebuild and have the existing engine rebuilt and keep it on the side. Thus, two engines for a little more than a new crate engine.

gps-marc

you can get the parts...what parts do you want? I rebuilt a cup engine and drove the car at the 2004 24 hours of Daytona...

email me at marc@2002racing.com if you have more questions.

Geoffrey

You may want to consider using the 7.25" Tilton setup from the GT3R which is legal in the PCA GTC-1 racing rules. I have this in my car and it is very nice, robust, and easily rebuildable.

Why are you going to trash the cases? Why not have Ollies align bore the cases and rebuild the engine using some of the newer 03-05 parts. Rick Deman has been rebuilding GT3 engines for awhile now and can do it for far less than PMNA does.

jrgordonsenior

That was the original intent until we saw the uneven wear on the mains. We think it was lined bored before and that may have been the problem. Also this engine has been rebuilt a few times before. The newer cases are slightly different and allegedly stronger. No decision has been made yet......