Motor centering

[dxhall]

I have begun another Exercise in Brain Damage in which I install a BSA Lightning motor in a Benelli Mojave frame.  Why, you ask?  Because (1) the Benelli frame is a copy of a ‘60s Rickman frame and (2) it’s a cool looking bike.   

So here’s the question:  it looks as though I will need to offset the engine a little to get the drive sprocket to line up with the wheel sprocket.  I wouldn’t think that the motor was perfectly balanced in the frame in the first place, but I am not sure what will happen if the center of mass (which always ends up to be somewhere inside the motor) is not on the axis between the wheel centers.  Any thoughts about how that would affect handling?  I need to find my copy of Foales’s book on motorcycle design.

[Diploman]

I doubt if offsetting the motor a bit to one side would have much significant effect on the bike's handling , provided that the engine sprocket and the rear wheel sprocket are well aligned.

Such an arrangement, however, might result in a lateral imbalance that could make the bike lean slightly away from the side to which the motor is offset.  To correct this, you could add some mass to the drive chain side:  eg. a 2-into1 exhaust with slinkier on the drive side; a front rotor and caliper on the drive side, etc.  The offset motor might look a bit odd, but at least it would be a conversation piece and any lateral imbalance could be evened up.

[oldbike54]

 Lots of British specials had offset motors , unless we are talking more than an inch you will never feel it .

 Dusty

[pehayes]

In Vespa virtually 100% of the motor mass is on one side of the center line.

Patrick Hayes
Fremont CA

[flangeman_70]

Centauro and could also be Daytona (4V Head) are offset approx 10cm to the right. I think it had something to do with getting the gearbox output lined up with the final drive. It’s never been a handling issue for me.

Adam

[Two Checks]

Iirc aren't some of the HD engines offset for the same reason?