Jump to content
Sign in to follow this  

balancing and oversize pistons

Recommended Posts

i increased the bore size on my cbr125 to 150cc. the standard piston weighs 98 grams i was using a low compression piston from a cbr150 which weighs 112 grams i now plan to use a high compression piston which weighs 130 grams. how much is too much weight before you need to re-balance the crank? the cbr150 (112 grams) piston had small vibes at high rpm but wasn't too bad

Share this post


Link to post
Share on other sites

Ideally, the crank would be rebalanced if anything changed weight.  But in as much as actually counter balancing every inertial force in a single cylinder engine is impossible anyway, and ends up being a compromise no matter what, you have to go by the results. 

 

The 112 gram piston was 14% heavier and buzzed a bit more than the original.  The 130 gram piston is 32% heavier, so one could reasonably assume that the vibration caused by the 112 will be worse by an exponent of that additional weight.

Share this post


Link to post
Share on other sites

thanks.i considered putting in the heavier piston just to see how bad the vibes were but its alot of work only to take it back apart again. the cbr150 piston sits down in the bore 2mm over standard so it has a ridiculously low compression ratio. i live in thailand so knowledge and common sense here is a bit thin on the ground

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×