Originally posted by IronMan
I'm still learning the trick of the trade and would like to share any information that I can find thru the internet .Hopefully someone who understand better can help to explain certain topics.OK I start with crankshaft balance .
Some notes on crank balance:
If you want to get fussy, and allow for the port being moved, balance on a "wheel" type balancer. This can even help on a stock type crank. (see some of the Russian engines, .15 size for examples). The amount of counterbalance needs to be in the 50~65% range of the weight of the piston,wrist-pin,(ring, if used) and 1/2 the weight of the rod. To test this, measure the weight of the reciprocating parts on a good gram scale, and make up bob-weights in this amount to add to the crankpin, before you put it on the balancer.The crankpin should "stop" at the 12 O'clock position. On a single cylinder engine: If you add weight to the counterbalance, or lighten the reciprocating weight. you DECREASE the PRIMARY shaking imbalance (vertical= Cyl. bore axis), and INCREASE the SECONDARY imbalance (crosswise= across the lugs).
For this reason, IT'S IMPOSSIBLE to balance a single Cylinder engine, without a secondary Balance shaft, as used in some auto engines. Adding weights (heavy slugs) to the counterbalance is done to change the resonant frequency at which you get a "Harmonic" or strong vibration level. You want this at a lower than full rpm number. Most of the ST X-40's used in Formula-1 Pylon and Fast Rat had cranks that needed this changed to resonate in the high-teens (RPM). Sometimes you could see the engine "shake" in this range, on the test stand. I never put a strobe light on one to see what one would look like while running. If the engine is balanced to "resonate" at full RPM, IT USUALLY COMES APART
Again some one might be able to eleborate this further.
Thanks
Hey very interesting point. Somewhere of the beginning of my present here in forum I mentioned about dynamic balance ( but someone call me irrogant idiot for it). This is what about. In many cases we just think about static balance ( when we work with engine on working table) try to weighing piston wrist pin and conrod. But when engine is working specialy at high RPM we have place dynamic balance, when wight are shifting from one position to other. In my opinion there can be real solution to get rid of unbalnce and made balance perfect. but there is ways to decrease it a lot.
Here in your post is mentioning some Russian engines with uncommon design of the shaft, it is absolutly tru. We can move some part of engine to one or other side which will help us to fight with this problem. On my new upcomming engine, I am using this trik- I have moved induction port to one of the side. We did it always in the past, no one Russian engine has induction port on the center. This design been use sometimes from mid 1980's
It is impossible to use the same way of improvement on existing common RC cars engines ( one of the point why I decided to make my own device). I am not saying existing engines are bad, I just think about this problem differently.
