This thread is confusing me. This IS the rack mounted drive train section, so exactly why is their any question about the engine being frame mounted? In a rack mounted engine the engine and drive system most often pivot up and down with the rear wheel if there is a rear suspension on the bike, or it would need to have a large chain/belt tensioner to account for the differential motion between the bike frame cantilever rack mounted engine and the wheel going up and down. Any 'squat' caused by the drive chain/belt pulling the axle upwards during acceleration is sort of the nature of the beast if the engine is mounted on a rack rigidly attached to the non-suspended part of the bike frame above the suspended rear axle. To eliminate squat the best solution is to mount the engine on a rack that is attached to the seat post via a pivot and braced to the rear axle via pivots. The braces hold the engine-axle a constant distance apart, thus eliminating accelleration caused squat other than the normal weight transfer squat inherent on any suspended bike. That would allow the engine to move up and down with the rear wheel, maintaining constant tension and distance/length on the chain/belt, and not pulling the rear axle up during acceleration. Drive could be routed to a pivot point at the pivot point of the rear suspension via idler sprockets/pulleys or a jack shaft, but the complexity and weight of such a system puts me off. When it comes to motored bikes, I go with the "keep it simple, stupid" school of design.