Hi
Bruce, and
ODK members,
Thanks for making the inquiries and finding this information for us... and Rover knew about this issue in 1991!
I didn't believe it could have been caused by a well used Briggs engine, but there you go....a Model 80202 is at the root of the problem and the fix is the new style inner clutch half (engine side) with 2 longer screws and the counter-weight.

I see you have the counter-weights already listed in the Online Store...anyone with a new clutch half and that model Briggs will perhaps need one, plus the replacement screws, if suffering vibration issues.
Well done mate, and thanks again for this info.
