OzVMX Forum

Clubroom => Tech Talk => Topic started by: Tomas on May 03, 2014, 03:59:53 pm

Title: crankshaft balancing
Post by: Tomas on May 03, 2014, 03:59:53 pm

Hello
Just would like to know if it is necessary to balance a crankshaft after it was modified and rebuild. The crankshaft in question is 1979 rm125 crank with 2000 rm 125 rod kit installed. New rod is touch heavier. What would be a simplest way to balance a crankshaft? Is it necessary to have piston installed when balancing?  I dont have any special tools etc.
Thank you for any ideas and help

Title: Re: crankshaft balancing
Post by: oldyzman on May 03, 2014, 04:24:24 pm

Good Question,
I await a silver bullet simple answer as i am interested in this also....

Title: Re: crankshaft balancing
Post by: 80-85 husky on May 03, 2014, 07:22:05 pm

there is a guy in qland who is on café husky and he has balanced cranks on a husky 250 and a 400 with good results, his forum name is Dukkman

Title: Re: crankshaft balancing
Post by: Brian Watson on May 03, 2014, 07:44:00 pm

or...of course..the best guy in the land....Frank Stanborough...Franks Cranks...used to be Graeme Smythe's Kwaka mech..very clever guy...

Title: Re: crankshaft balancing
Post by: Lozza on May 03, 2014, 09:08:40 pm

Quote from: Tomas on May 03, 2014, 03:59:53 pm

Hello
Just would like to know if it is necessary to balance a crankshaft after it was modified and rebuild. The crankshaft in question is 1979 rm125 crank with 2000 rm 125 rod kit installed. New rod is touch heavier. What would be a simplest way to balance a crankshaft? Is it necessary to have piston installed when balancing?  I dont have any special tools etc.
Thank you for any ideas and help

Depends on how many grams "a touch" is ? There is no 'simple' way to balance a single cylinder crank as the balance factor is a % of reciprocating over rotating masses. The only simple answer is to try it. If it shakes your fillings out or the handlebars feel like the size of 2inch water pipe you will have to rebalance the crank   

Title: Re: crankshaft balancing
Post by: Tomas on May 03, 2014, 09:47:00 pm

Just find some informations about how is it  done here if anyone is interested. http://www.xs650.org.au/Club%20Racer%20Stuff/Club%20Racer%202013.htm (scroll down)  It is not that hard at the end.

Title: Re: crankshaft balancing
Post by: Michael Moore on May 04, 2014, 02:15:15 am

This article by Tony Foale will help you understand what is going on:

http://www.tonyfoale.com/Articles/EngineBalance/EngineBalance.pdf

Tony also wrote a little program for single cylinder balance factors that you can download here:

http://tonyfoale.com/progs/BF.exe

cheers,
Michael