I wonder if any of you here can walk me through the procedure to balance an engine? I have a K&B .40 that has a lighter than stock piston and rod. I don't want to approach this project with a hit and miss, or grind and pray method!

Post #35 in this thread http://www.rcuniverse.com/forum/fb.asp?m=3032044 had a very vague description of how to do it.

Hi!
How much lighter is it?
In pylonracing it was common thing many years ago to lighten the piston and rod as much as possible to make the engine perform better. This was before the Nelson and IR (Russian pylon racing engine) era.
Regards!
Jan K
Sweden

another thread: http://www.rcuniverse.com/forum/m_11...lancing/tm.htm


my method: make a weight that is equal to 3/4 of the rod's weight and half the complete piston assembly weight, hang this on the crankpin and balance away...


dave

Yet another thread at SSW (if it works).
http://clstunt.com/cgi-bin/dcforum/d...rum=DCForumID1

over there i found: "All the upper end components minus 1/2 the weight of the rod bottom end." add this to the 50% and 100% rules and you've got lots of choices... so instead of actually grinding anything why not just make up a new formula that matches the balance your engine already has??


dave

Thanks for all the replies, guys. You're right, DAVE, I could just make up my own formula and find an rpm range that it doesn't vibrate at, like 500 or so. With all the different methods, I think you have to consider the application. I don't know enough about it to be able to follow even my own advice! I guess find advice that closely follows what I'm trying to do, I'm trying to get a .40 to run smooth at 24,000+.

the 50% rule works good for me at those speeds. rotating parts (crankpin and bottom half of rod) are fully balanced and reciprocating parts (piston and top half of rod) are 50% balanced. if your engine was close with the original parts then it may only need a couple of small holes drilled in the crankweb.



dave

I've read enough Clarence Lee tests over the years to know that many times an engine that falls outside those rules will run smoothly.