So we were supposed to be racing at Donington Park last weekend, but it wasn't to be...   We went on a track-day the day before and all was going well - it's a fantastic track. Just before the end of the day my team mate when to shift from 4th to 5th @7600rpm (110mph) and hit 3rd.   I've worked out the engine probably hit 9200 rpm momentarily, the clutch was dipped very quickly, amazingly the engine seemed fine and my team mate continued for another half a lap with no obvious signs of an issue... Then the engine just died - no power and backfiring.   We couldn't work out what was wrong - cam timing measured up ok, compression a little down on one cylinder by not enough to stop it running. In the end we suspected the ECU as the engine would crank over with compression but was popping and banging out of the throttle bodies - so we had to miss the race and get it back home . Plugged in laptop when I got home and all seemed fine with the ECU so still a mystery...   I tried starting it again on Monday, and all of a sudden the engine stopped rotating and there was a horrible grumbling noise - the flywheel was spinning without the rest of the engine!   I think the flywheel bolts went, and then the flywheel friction welded itself to the crank in the wrong place hence the timing being off!     See below pics:     I'm a little worried about the state of the crank flange, the most damaged side of it is shown below:       It's taken a right hammering!   I should be ok removing the bolts and dowel - the dowel is only case hardened so I'll drill and tap it for an M6 bolt then pull it out, but I'm a little concerned I won't get the flywheel exactly centred due to the damage to the end of the crank.   I put the damaged flywheel back on without the locating dowel in place to see how much movement there was - in one axis there was none, but in another there was about 0.5mm.   Am I right in thinking that once the bolts are done up it's the friction between the flywheel and the crank that takes all the drive force? In which case it doesn't rely on a super tight fit between the flywheel and the locating flange on the crank? If so with the dowel replaced I think we'll get away with it.   My plan is to get a TTV lightened flywheel fitted while the box is off and see how we get on - it'll be pretty obvious if something's amiss due to vibrations. Looks like the engine will be going for a rebuild at the end of this season so I can get my spare crank in it, but I don't want to miss the last race of the season at Oulton Park...   What a pain! To be honest I'm quite impressed there's no apparent internal damage to the engine after it hit such high rpm (MI16 on stock internals and valve train this uprated cams so very little piston-valve clearance!)