Shake rattle and roll
I installed a rebuilt YSM 12 in my S2 8.5. It seems to vibrate especially in idle. Is this due to being a one cylinder? I owned several boats but none had a one cylinder engine.
When I first went to look at my S2 8.0C I brought along a friend who was an Atomic 4 fan. We cranked up the YSM8 diesel in the boat and his eyes got very big and round. He looked like he was expecting the thing to throw a rod.
Hundreds of yours later I am still going strong, listening to the sweet sweet sound of "marbles in a tin can"
Yep they bang around quite a bit and at Idle sound like they are comint apart.
One thing...check your engine mounts and mounting sringers. S2 had issues with inadequately tabbed mountings. Easy fix, but a walking single cylinder would be scary a thing to see!