Originally Posted by leadfarmer
I see, you are moving the engine forward to tighten the chain.
To be honest, while shimming the engine mounts may be necessary for a proper fit of engine to frame, this may not be the best solution for chain tensioning for anything other than a show bike or weekend rider at most.
Commonly referred to as chain "stretch" you'll find that you'll need to periodically adjust to compensate as the sprockets and chain wear - while quite pronounced when the chain/sprockets are new and will lessen with use, it never actually stops & the more you ride, the more often you'll need to make minor adjustments.
This is what horizontal dropouts (move wheel back to tension), adjustable idlers and/or tensioners are designed to help with and while it may take a little extra effort to incorporate into your build, if you plan to be a frequent rider, that small effort can save you lots of headaches later.
Sure, you may have a couple of spare shims, a ratchet and loctite with you at all times, but I think loosening the one bolt on an idler, moving it slightly & tightening again to be a lot simpler roadside adjustment/repair than messing around with your motor mounts, only to find it wasn't quite enough, a little too much or worse yet, a messed up mount - remembering ofc that if you shim just the rear mount, the angle of the engine changes which can stress the front mount. You can raise the front mount to compensate, but now you're messing with all of the motor's mounts and as some down tubes aren't straight - you're still messing with different mount angles.
Still, to each their own - if you don't plan on riding much or are more concerned with a "clean" look than function alone, moving the engine around just to adjust the chain might be the solution for you... *shrug*