ive recently had the crank re-shelled on the big ends, it was running fine for about a months, did plenty of miles on it no probs. i did a compression test on it a few weeks ago, and the compression was great. i was riding it back from work the other day, no probs, then when i went up the bypass near my house, i accelerated up to speed, then whole bike jaulted a bit, then a heard a realy big crunch and a loss of power. so i coasted to the side of the road. the engine was still running, but there is a very pronouce tapping sound on the revs of the engine, rev it faster, the tapping gets faster, which maybe tells me its probably on the crank? any help would be great as this is my only means of getting to work. thanks folks.
josh.

No good news there.

If your crank is moving inside the bearing shells the bike should be vibrating to buggery I think (anyone confirm?)

Seeing as it has recently been worked on I would be having them investigate it and fix it, chances are it's related.

Also, don't run the engine, if it is the crank you'll be doing no end of horribleness inside the crank cases if it has knackered a bearing.

deleted, wrong thread, woops

a few people have suggested a dropped valve or bent valve, crank bearings, or a piston ring has gone.