"JAXAshby" wrote in message
...
One thing you have to deal with is thrust from the propellor and shaft.
Car and motorcycle engines and transmissions don't have thrust bearings
as in a marine transmission.

They sure do. If they didn't, they wouldn't last very long.

What utter rubbish!
There are motorcycles out there that will withstand thrust directly down
the output shaft?
Frankly i dont belive you.
even shaft driven bikes tranfer thier power through turning motion only the
shaft is only subected to torque. not thrust.

A boat prop Pushes the shaft forwards... which via the gearbox
bearings......pushes the engine... which takes the boat forwards with it cos
its bolted to the boat!
Its one of the reasons that boat engine mounts are a tad more costly than
engine mounts for almost any other use.
Select reverse.. (not a lot of bikes have reverse... a few.. but not many)
and the shaft pulls .. I'd guess that would be very sudden death for most
non marine gearboxes.