Hi MickKelly, and a warm welcome to the forum. It's always nice to welcome aboard another Scott Bonnar Model 45 owner, as we all like to learn new things and tinker here. wink

I would have to agree with BB that a worn inner clutch half maybe the problem here...and it is a shame that the really early cast iron clutch bodies are no longer available. cry

Having removed the Briggs engine, is there any evidence of cracking in the engine deck rails form all that vibration?
If so, that will have to be addressed before we go any further.
Unfortunately the pics of the chain case area are not close up enough for me to access the condition of the chains and sprockets...could you please upload some more particularly of the sprockets where not`covered by the chains? Thanks mate.

Don't be afraid to ask questions, as we are here to help you through this problem.
Once again, :welcome: to OutdoorKing.
cheers

Please do not PM me asking for support. Please post your questions in the appropriate forums, as the replies it may receive may help all members, not just the individual member.
Kindest Regards, Darryl grin