Crankshaft offset grinding
 

I planing to increase stroke of my engine. Please let me know what is the best way to increase stroke. ( my idea is to grinding crank shaft)

Re: Crankshaft offset grinding
 

you will need to have to pin relocated rather than offset ground.

offset grinding would require a smaller inner diameter bearing once you have finished.

it may well be possible to buy a crank for another engine size to gain extra stroke (120cc stroke is often longer that 125cc for example)

Re: Crankshaft offset grinding
 

I don't know much about Pit Bike engines, but I know quite a bit about Big bike and Car engines.

If you are going to have the big end re ground off set you are going to have to fit a con rod with a big end to match the now smaller diameter.

You are also going to have to make sure that the new Stroke of the piston does not poke out above the deck of the barrel, if its a 2 stroke it may hit the head, if its a 4 stroke in may clash with the valves or hit the head.

If its clear on all of the above, you will probably need the barrel re boring. Under normal running a "lip" appears near to the top of the barrel which is at the end of the stroke for the rings, if you just install a "stroker" crank the rings will catch this lip and do damage.

Of course things may be different in the Pit Bike world.

Re: Crankshaft offset grinding
 

If it's a YX140, Parker racing sell off-set crank pins to increase to 150cc.
He also sells YX145 barrel/piston kits.

With this combo, you can see a YX140 up to about 156cc I think.




Hope this helps


Ben