You really need to volunteer more information. Also a sound bite of the noise would help.[/QUOTE]
Sound bite! I'm no more a computer whiz than I am a mechanic, I've got my mechanic pal coming to have a look tonight, we'll do a compression check and get his bore scope in to have a look to see if there is anything obvious, the general concensus is that its small end bearings, the compression check should let us know if the rings have gone.
I've checked the gear box on the other boat, its prop will turn one way by hand when in forward, my one does the same but when in reverse???? dont think there is a problem there though, deffo an engine knock, I'll try what was suggested, removing a plug ground it out and fire it up to see if the cylinder goes quiet, whatever it is, its a strip down for sure