Is the 66cc supposed to shake this badly?

[moronic_kaos]

In simplified terms, a single cylinder engine can not be truly balanced. The best that you can achieve is a slight out-of-balance condition at an RPM that is normally not used for more than a brief moment during acceleration.
Jim

Ok. So I read up on this a little, and what it looks like is in a v-twin (keeping things simple), there's two cranks that are in completely opposite positions at all times, equaling out the balance no matter what position the pistons are in, be it TDC, opposite or that, or anywhere in between. But in a single cylinder you've got no counterweights. Makes sense.

So how does one calculate what the offset in balance should be based on desired RPM band?

Not that I'd try to make a perfect one, but I'd like to be able to at least be able to check some existing ones (rate it good, better, best), or maybe try and fiddle with it a little if I got some ambition.

 

[foureasy]

right idea, wrong example. a v twin has a single journal on the crankshaft, which essentially makes it a single cylinder for the purposes discussed here. my balanced and trued cranks move the sweet spot higher in the rpm band with a resulting, out of balance condition in the lower range. very similar to my panhead which also shakes at idle.
it took me 3 or 4 tries on how much to remove to get it just right, but i have never reverse engineered it to find that percentage. if you wanna try it yourself, just remember that removing weight in the crankpin area of the wheels will move the "sweet spot" up in the rpm range. how much exactly?

 

[moronic_kaos]

Oh. So the weight isn't being shifted to the left or the right like I thought you guys were talking about. The things just getting lighter in general (while keeping good balance)?

Easier concept to think about.

Thanks.


So I'm guessing a lighter flywheel doesn't vibrate as much as a heavier flywheel for the same reason a 1 pound weight shook around in a coffee can vibrates less than a 2 pound weight. In order to minimize vibration when shaking the can harder (as in more RPM), less weight should be used. But here's where it gets confusing to me.

Why does it rattle more on the low end if it's lighter?