DE STROKED MOTORCYCLE

[thundair]

Is it OK in the rules to stroke a motor to get to the right cc
Some what like the 654cc BSA, it's not a 650 but oh so close.





Please have a little patients with me I am old and dumb, but love racing anything.

[1212FBGS]

Yes.
kr

[Nortonist 592]

You can stroke or de-stroke motors to getto whatever capacity you need.  In the case of a 654cc BSA if you de-stroke it to get under the 650cc limit you cannot run it in production class.  If you have a 654cc BSA you would be better off to stroke it out to 750cc and run in the modified production class.

[1212FBGS]

what year is the bike? is it gonna run vintage?
ok... check it out... de stroke it to 650 with std bore size (shorter stroke, spins faster).... then bore out .020 allowable overbore (.040 for vintage, unshrouds the valves for better flow) and race in 650 class 

[Hans Blom]

But you still can't run it in any kind of production class, no matter how you stroke/destroke  , overbore/underbore. As long as it started life as over 650, any kind of production class you will be with the 750s....

[1212FBGS]

correct.. you cannot destroke to get into a production class. OEM displacement determines class. But you "CAN" bore and stroke your 654 to the production class max of 750cc.

[JackD]

The OEM basis for a production engine size came from a participant at a convenient and regularly scheduled forum with all the players.
It met with the universal approval of all without exception.
That information resulted in some proposed wording changes that had the same level of support on the spot and resulted in unanimous board support as appropriate.
It was not a daytime on the salt or lack of available space in town that only lacked a budget for something that never cost anything in all the years prior.
Connecting the dots is really easy.