Production Class Motorcycle Displacement

[DanMay1776]

I have read the rules for production motorcycle displacement:

7.J.1 Production:
Production engines must be the same model as the model of the frame being used and must have STOCK
EXTERNAL APPEARANCE. Production motorcycles must use OEM cylinders, heads and crankcases to comply with this class. OEM engine displacement determines the displacement class for competition. Displacement may not be increased beyond that class limit.

In my case, the 250cc production vintage, my bike came stock with a 247cc displacement (68mm x 68mm).  I need to go one size over due to wear, which is a 68.5mm piston.  This will put me at 250.6cc.

Do I get bumped to the next class since I am technically over 250cc ?  My other option is to re-sleeve back to stock, but I want to be certain I can remain in the 250cc class legally.

Daniel

[Stainless1]

sounds like time to move to modified...
unless ECTA follows the SCTA vintage rule that allows an overbore for production vintage motors...
call Todd Dross or email him on this site.

[dr j]

Dan, in the ECTA rulebook under 7.J.10 Class VG and VF it says
"A .050 in. overbore is allowed on vintage engines only (including production vintage) and will be discounted when the bore size is measured."
Now you did not say what the overbore "one size" was for your gorgeous BMW 250 but I would hope it is less than 1.27mm which equals .050".  So then you should be fine by my reading of the book.

[DanMay1776]

Jarl, You beat me to it.  I read the ECTA rules a little closer, I found this:

"A .050 in. overbore is allowed on vintage engines only (including production vintage) and will be discounted when the bore size is measured."

So do I interpret this as being able to go 0.05 in (or 1.27 mm) over , the first over piston is 0.5 mm, going from 68 to 68.5 mm.
So it looks like I can still be legal going +1 over to 68.5mm, and for that matter, I can go to +2 over if needed in the future to 69 mm, but not +3 over which would be 1.5mm over, exceeding the 1.27mm limit.

Does this sound right ?

Daniel

[dr j]

Jarl, You beat me to it.  I read the ECTA rules a little closer, I found this:

"A .050 in. overbore is allowed on vintage engines only (including production vintage) and will be discounted when the bore size is measured."

So do I interpret this as being able to go 0.05 in (or 1.27 mm) over , the first over piston is 0.5 mm, going from 68 to 68.5 mm.
So it looks like I can still be legal going +1 over to 68.5mm, and for that matter, I can go to +2 over if needed in the future to 69 mm, but not +3 over which would be 1.5mm over, exceeding the 1.27mm limit.

Does this sound right ?

Daniel

Yes, if the stock bore is 68mm then you should be able to go up to 69.27mm and still be considered a 250cc production vintage (or VG or VF as the case may be).

[Warp12]

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