bizarre and worrying non-start problem...

[Gav P]

'69 912 (not mine anymore) was running fine until a week ago. Pulling away from a junction the engine died and it hasnt started since. When checking out back, it turned out that the generator belt had failed and had come off the top pulley, but hadn't snapped completely.

All attempts to start it again have failed, having checked the timing, fuel, spark etc all seems to be fine. Occasionally we get a huge backfire and thats all - suggesting to me that the timing is way out. However, static timing has been set properly and rechecked. The engine turns over on the starter, although I have to say it does sound different to how it used to when spinning....

However, the most worrying thing was that when I checked the valve clearances, three of the four exhaust valve clearances were at about 3mm clearance!!! All tappets were adjusted to factory spec about 400 miles ago and the engine was running very sweetly, so for this amount of free play to appear I'm thinking something fairly scarey must have happened in the camshaft/follower department.... very strange that it was only the exhaust valves and not the inlets which were out though.

Have not emptied the oil out, but there was no debris in the oil of the rocker covers when they were removed.

Im starting to think there may be some kind of failure in the timing gear, such that the dizzy and the crankshaft are no longer in synch with the camshaft.. must be a pretty drastic gear tooth failure or perhaps woodruff key on one of the gears?? Others have suggested collapsed cam followers - seems a bit unlikely for several to go at once though..?

Any ideas anyone?

Cheers for now,
Gavin

[WFBowen]

Gavin:
Just as a starting point I'd pull all of the pushrods out to be certain that none are bent. Then pull the sparkplugs & slowly turn the motor with a wrench & feel for any binding, etc. While # 1 plug is out, I'd take a plastic straw and verify that TDC and the distributor rotor are in sync. Since the belt failed during/leading to the motor problem, the logical question would be: Is there a possibility that this motor momentarily saw 9000 rpm?
Good luck,
Bill

[Gav P]

Thanks bill, sounds like a very good place to start... will be giving those a go..

Cheers, Gavin