Reply To: 6039 Speeditwin Piston Removal

[jacksonm29]

Something just occurred to me…this was the motor with the broken prop shaft right?
If so, I submit to you that this worn crank taper is/ was the root of the problem.

Loose flywheels on big opposed twins will cause a serious back and forth knock all the way to the shear pin. Especially at idle.
Sadly, i had this happen on a PO-15.
Ruined the crankshaft, flywheel, and sheared the 5/16 shear pin. All in about 10 minutes.

I have 4 running 6039s and several leftover parts and pieces, but I have no good crankshafts.

For me ( and I am a machinist) I wouldn’t fool with welding it up and recutting the taper and key.
Also, I would guess that the flywheel bore is pretty rough as well.

I’m sure a good crank can be found.
Also something to consider, the crankshafts seem to be fitted to their particular lower bearing/ rotary valve assembly for a good seal.

Mark