Torquer

When getting rid of the pull start from an OS21, can you simply cut off the start pin on the crankshaft or will this cause a balance issue? I know the pin-less crank is available but just want to know if this is doable?

Square Nozzle

My Feedback: (1)

If you look at it from a purely dynamic point of view, it has to impact the balance. Is it a clearance issue that requires that you remove the pin? If it were me, I'd cut it off and see how much vibration is introduced. I can't believe that the engine manufacturers pay a lot of attention to balance once the design is finalized.

jetpack

My Feedback: (1)

It might be a slight enough of a change not to notice, only your bearing life will tell you. I would leave it. Why cut it off just to find out you made a mistake. If you already done this and notice vibration, you'll have to lighten up the counterbalance which is all a hit and miss operation. 20,000 rpms is quite high to play with and measuring the balance of one of these is quite touchy.

The best way is to take comparative measurements between the two types, as far as counterbalance dimensions. If both versions mic out the same, and the pinned version is heavier then i would say you are safe.

Torquer

The reason to remove the pin is to be able to use a cover plate in place of the pull start. There are two cranks availableā€¦one with the pin for pull start and one without the pin for non-pull start. Iā€™m just wondering if the pin is just simply a pressed add-on to the non-pull start crank or is it machined in with counter balance.

ryan_t888

Judging by the photos I looked at, I can not see any differences. Of course I can't make out a difference of a few thousanths of an inch if there is one.
I agree with the last statement John made. "I can't believe that the engine manufacturers pay a lot of attention to balance once the design is finalized. "


No matter what you do, you will never be able to completely balance a single cylinder engine.

Ryan