CMB 91 Drum Holes

[Mike Rappold]

On the CMB drum, see photo, there are two holes in the "disk" section. One is for the drive pin on the crankshaft. What is the other for? The diameter of the other hole is larger than the drive pin one. I am guessing it was using in the machining process but wanted to ask the group. Thoughts?

Since it is not used, has anyone ground it off to lighten the rotating mass and better balance the drum?

Thanks in advance.

Mike

 

[Andy Brown]

Mike, I'm fairly sure it's purpose is only balance. They just did not go far enough to get it balanced. A little grinding near that area will do the trick.