Loose Flywheel

[VYT]

Chaps,
Mate of mine in the US has a 997 GT3 2008 model that he tracks quite a lot. On the last outing he thought he blew the engine but further investigation shows that the flywheel has detatched from the crank. Seems the bolts sheared. As a mechanical engineer, I find this hard to understand. Anybody on here ever heard of a similar problem? One other bit of information is that a lightened flywheel was fitted sometime ago.

Cheers in advance.

Bob

[gtphile]

I have never seen a flywheel bolt shear, unless the bolts weren't the correct hardness. I would be more inclined to say they weren't torqued in the first place, and have come loose.

Ask to see the sheared bolts!

edited for spelling

[phelix]

Or they reused the old bolts which had previously been torqued to yield?

[VYT]

Thanks guys.

[fergus]

Assuming the gt3 uses a 6 bolt crank, even if non nms or arp ultra high tensile strength bolts were used, how could the flywheel shear all the bolts holding the flywheel on?

Given the clutch mounts on the flywheel, this would have completely fu<ked the clutch assy surely?

The flywheel also acts partially as a harmonic damper for the crank, so I would be stunned if the big end bearings are all ok?

I think there may be some facts missing here?

Skippy/Neil (fioran0)- where are you?

[BertBert]

In the caterham world I have experience of this. My R500 had done about 450 miles from new when I took it out at Donington. The engine failed when the front crank pulley fell off as the securing bolt had come undone. When the engine was taken out and parted from the box, the flywheel fell off as the bolts had sheared/fretted away.

This was a complete mystery and Caterham/Minister wanted to put it down to kerb-hopping at Donington transmitting mechanical shocks to the engine. Except it was a gentle track day with certainly no kerb-hopping.

It was then remembered that Caterham had changed the flywheel at post build check owing to a ring-gear problem. The flywheel/crank assembly hadn't been balanced as it would have been in the new engine build.

So potentially quite similar circs and vibration being the acknowledged cause.

Bert

[Lagerlout]

Yes, had this happen on a couple of cars. It's not that unusual. When an engine maintains maximum revs, or over revs for an extended period of time this may occur. It's better than lunching the entire engine.. Not sure if it's designed this way, but it's a good way to stop an engine quickly. It's particularly useful in cars that have a propensity to have the throttle stuck wide open.

[fioran0]

Not common but I know of a couple of 996 cups and one 996GT3R that have had flywheels come off/loose and rattle around inside the bell housing. Lighter flywheel and any sheared bolts havent been primary failure but its data at least. Since 997 Cup and 996 RSR the cars have used an entirely different clutch setup (5.5" triple plate setup) and flywheel.

Tbh, that OP isn't much to go on though is it. Have you more details? You should check your friend hasn't gotten the wrong end of a stick and also what else is damaged.
It's far more common for the rivets to stretch/fail on the pressure plate. Vibration is terrible but not everyone is as observant as you would think. Left unchecked the imbalance could quickly fatigue other parts including flywheel bolts.
A missed shift over rev is what stretches the pressure plate rivets.

Did he change his front pulley when the lwfw was fitted. Folks that didn't had various problems but I've never heard of a flywheel being one. Someone always needs to be first though

Edited by fioran0 on Friday 18th January 00:44

[Rockster]

VYT said:

Chaps,
Mate of mine in the US has a 997 GT3 2008 model that he tracks quite a lot. On the last outing he thought he blew the engine but further investigation shows that the flywheel has detatched from the crank. Seems the bolts sheared. As a mechanical engineer, I find this hard to understand. Anybody on here ever heard of a similar problem? One other bit of information is that a lightened flywheel was fitted sometime ago.

Cheers in advance.

Bob

As others have suggested the flywheel bolts were reused. I had a VW Golf TDi in for a new timing belt and the engine mount bolts were reused. They are supposed to be replaced but the SM lied and told me that had been changed by VW. After some miles the bolts failed and the engine fell down. Lucky no harm done but it cost me hundreds of dollars to have another shop replace the mounts and use new bolts.

The LWFW might be the culprit too. If it is "soft" the bolts may have crushed/compressed the LWFW material and thus come loose.

This might have been helped along by the fact the stock flywheel also serves as a vibration dampener and with this functionality gone the LWFW ight have experienced more vibration which helped the bolts compress the material and eventually come loose.

Or the bolts were not the right ones, too soft. To some "mechanics" bolts is bolts and that of course just ain't the case. Or they were not installed/tightened down correctly. Tighten to yield bolts have a very specific installation/tightening sequence.

Or one of the bolts was just bad. It happens. That is why new parts generally have a warranty. To deal with the ones bad out of the box.

Trouble is you'll likely never know what happened. And chances are it will never happen again.