Posts: 3508
Location: Elk River, Minnesota | If it is a big "clunk", I would highly doubt a prop slip... A motor of that year uses a shear pin. So..if the pin sheared off, it would not spin and no forward movement would happen.
I'm wondering if it isn't something with the gears in the lower unit, though... Might be missing a tooth here and there, and when the gears hit "just right"...the clunk happens. It might be simple as a shift linkage adjustment (if that motor has that capability) too...but if it's in gear and on plane, that doesn't sound like it would be the problem.
A tell-tale sign of gears missing or broken would be to drain the lower unit and see if there are pieces of metal in the gear oil. If so, it's rebuild time if you want to keep a beautiful timeless piece of engineering going, or it's time for retirement and display... Parts should still be somewhat available for the motor if needed (from a place such as twin city outboard)
Steve |
