1955 panhead crank and flywheels year oddity

[flatheadDave]

A friend of mine inherited his dads 1955 Panhead. And ever since he got it, he’s had a terrible vibration coming through the whole entire bike.

So we checked the frame for cracks, we checked the main shaft on the transmission, took the entire transmission apart, we also checked a bunch of other things like front end, checked for broken motor mounts, and just tried checking every where this vibrations might be coming from. Whenever he rode on the highway the bike would just shake incessantly. And we also change checked the transmission bolts to the frame. But nothing looked strange or odd or broken so we figured it must’ve been the fly wheels maybe they were out of balance or never really got trued or balanced correctly. Maybe one of the fly wheels shifted and the whole thing was just out of whack.

So we tore down the motor and brought the fly wheels down to a guy in Downey California who’s really great Filthy Phil.

“Original motor sprocket shaft was loose and pinion shaft wobbled plus flywheels needed to be balanced. 55 was the first year splined motor sprocket shaft and Christopher's bike happens to have the early style which were prone to come loose so the conversion to a later splined included milling some meat off the FW. “

They brought the motor back to my friends house and installed it in the bike and when he was cranking down the compensator nut, the engine bound up. Before we can even start it. Before we can even ride it! We have to pull the whole engine out again and disassembled it .

We brought it back down to Phil and look what happened in this picture. My friend Christopher was cranking down the compensator nut with an impact gun and sheared the lip off this shaft. Phil found another shaft installed it, re trued the fly wheels right then and there . We brought it back to his garage and installed it again into his bike. And 3 weeks later, it’s running fine now.

What’s the torque lbs for a compensator nut anyways? This must be some cheap grade steel to have this happen. Anyone else have or had a 55 panhead?

[RUBONE]

'56-'69 left flywheels are common. No need for machine work on a '55 flywheel.

[Andygears]

Couple things, first, that shaft looks to have almost no radius where the flange meets the body in the relief groove. You can see by the even crack that rather than a square edge relief groove, a radius should have been cut to minimize stress cracking. You don’t mention who made the shaft, but maybe it was originally from China and cut from crappy steel or hardened poorly.

Second, cranking down the compensator with an impact? An early compensator with the large spring? Don’t they have a flat plate for a pin spanner? Did you have an adapter of some sort? And, it’s been a while, but I thought those compensators tightened down against a shoulder on the shaft keeping a fixed distance for the spring to work in. The threads in the compensator nut should not have pulled the shaft from the flywheel unless the Timken main bearing assembly was incorrectly spaced, or the flywheels in the case hit, or the shaft, that broke, was made wrong.

Did you bring your cases to Phil initially so after he did machining on the wheels he could try them in the cases?

Andygears