Crank Case Grinding

[lok]

How much power is lost after machining the crankcase for a 105 kit and then using the stock top-end??

 

[cr25096er]

Why would you do that?

 

[MikeS]

It should not be that bad if the 105 kit was just the overbore kit.

A friend had a 105 YZ and swapped another 85 cyllinder back and forth. His 105 ate pistons real bad :(

 

[lok]

Originally posted by cr25096er
Why would you do that?

Depending on the track rules>>It may be neccessary to run with the stock cylinder.
It did seem to have a small noticeable power-loss?? At least if i were to time lap times form one race to the next on the same track.......We race tt and dirt track.

 

[MikeS]

It should not be alot. The rider feeling the power difference is going to make things seem slower in some cases. Maybe some tuning and jetting can help get the feel back.

 

[Jasle]

Not too much I'd think. but you change the crankcase volume when going to the big bore kit with the grinding so you might be trying to force too much volume in to the smaller bore. This is a great question for Eric Gorr. It might fit well in his forum...I don't think he treads over here too often.

BTW in most stock class rules if you have modified the case then even with the stock top end you could still get nailed. Depends on how they treat the teardown. If the just pop the top and measure bore stroke or do they take off the entire cylinder. If so they might notice the modifications. I'd probably only be worried about something like that at the Loretta qualifiers.