Motorcycle displacement issues...

[Hans Blom]

Is there any special rule or fact that deals with the fact that , for example some bikes that are 650cc are actually 654cc to begin with? I know you are allowed a minimal overbore, but what if you are at 654 go your first over size .....

thanks, hans

[1212FBGS]

if your bike is 654 to start with it would be legal for the 750 production class not the 650 production class cuz overbores are not legal in production. if ya are running M or A classes you are allowed a .020 overbore. +20 on a single isnt crap... +20 on a 4 or 6 cylinder may put ya close to 700cc!!!! still legal for the 650 class. feel lucky cuz the car boys arnt allowed any overbore past max displacement for class. but dont get caught cheeting they'll take away all your points, your momma's points and keep ya from getting points for next year........ LOL
kent

[sickracer]

[/quote]. but dont get caught cheeting they'll take away all your points, your momma's points and keep ya from getting points for next year........ LOL
kent[/quote]

When you cheat you need to be penalized!!!!!!!

[Seldom Seen Slim]

Hunh -- 650's are really 654's?  for years I've told my insurance companies that my (for instance) 1200 is really an 1199 -- I say "The factory builds 'em that way so we can have an insurance rate for the 1100 - 1199 size, not the 1200+ size.  And 600's are really 599, and well, whatever.

Nancy's 250 measured out to 249.7 -- Dale Martin measured it, gave me this quizzical look and asked if we had done a cleanup bore on it -- No, but I'll spray it with the CO2 next time just to be sure.  Or maybe we'll just show up in impound with the engine resting in a block of ice. . .

[Nortonist 592]

If your motor came from the manufacturer with a displacement of 654c.c. then you are in the 750 class whether it be production, A, or M.  If your motor came originally and a 649c.c. and you cleaned the bore out to 654c.c. then you are in the 650 class.

[JackD]

All of that was started for the sole benefit of a friend of the lone tech guy with a 2 smoke. The first year he tried to get it through it was determined to not be required for the bikes anymore than anything else. The overbore means something different for every engine size and has no more validity now than it did then. When it was explained to the board they shot the idea down. The next year it snuck by them like so many other things and is ridicules.

[Nortonist 592]

Very true.  The point I was trying to make was that if a motor comes from the manufacturer with a displacement of 654 c.c. then it falls into the 750 class.  Or am I reading the rules wrong?  Does a 654 c.c. motor that comes from the factory with that displacement qualify as a 650 for the purpose of class definition?

[JackD]

If I lost a bore size in a modern bike I usually could just resleeve it. In a vintage bike You might want to resleeve it to get it back to stock pistons you have, recover an otherwise damaged jug, or even increase the material strength.
I really doubt very many have used that abortion of a rule but that is not as bad as what they want to do with the cases.
REMARKABLE

[JackD]

If your motor came from the manufacturer with a displacement of 654c.c. then you are in the 750 class whether it be production, A, or M.  If your motor came originally and a 649c.c. and you cleaned the bore out to 654c.c. then you are in the 650 class.

You read it right the first time, that doesn't make it right with the rest of the world.

[Nortonist 592]

Thank you.  I never was any good at reading between the lines.

[1212FBGS]

hans
what kinda bike are ya talking about?

[JackD]

What the rule means when you read it is not always what they meant to say.
 Why they even tried to say it escapes the logic of many.

[Nortonist 592]

So when the rulebook says 650 c.c I might be able to sneak in a turbo Hyabusa without them noticing?

[JackD]

Halfa Busa anyway.
Be sure to safety wire your drain plug. I know you cant use a car for an example , but look around.

[Hans Blom]

Wow, never imagined this much response, great! Specifically a BSA A65. They have a 75mm bore and a 74mm stroke which comes out to 653.8cc. I am building a bike to run in several modified classes. No production at the moment. I will having custom pistons made anyway, if I have to I guess we could sleeve and machine some pistons a hair smaller, but I would rather not.  With a stock stroke I would need  a 74.78mm bore instead of a 75mm, not taking any honing into account.  It's funny, I'm not sure why but some manuals will list all a65 bikes as 650cc except for the Lightning Clubman which is listed as 654, but this is just in the specs, it was called a 650 like all the rest.  I want to do this not only for the fun of it, but of course I want MY name in the record book too! I would have a hell of time competing with 750 Trumps and HDs and my little 654 BSA....