100cc classic production build

[Stainless1]

from the 2021 book

[salt27]

To be clear, is the plan to run SCTA, AMA or FIM?

Or all of them?

  Don

[roflhat]

Thanks for that, have sent Russ an email

the plan at the moment is BMST this year for AMA records

[Stainless1]

If you are doing AMA you need to send questions to tech@bonnevillespeedtrials.com and/or info@bonnevillespeedtrials.com
The guys I threw out there are all SCTA contacts. 
Drew Gatewood (AHG), the AMA and FIM inspector is on here occasionally.  His email is gears55@frontier.com

[roflhat]

Ah excellent thanks, emailed them

[roflhat]

Been having a read through some posts on the forum and the rulebook. Not entirely sure if I'll get away with the liquid metal I used on the carb inlet to smooth it off. Anyone know if that's allowed?

[Stainless1]

Well you are not changing the venturi size... that is determined at the throttle plate.
This from the AMA rules

1. Production (P)
a. Use the same engines (gasoline only) originally installed
in the specific motorcycle frame at the time of production
and ensure it meets the definition set in the ?P? frame
class (See 3.11D). Original equipment (OEM) shall
include cylinders, cases (crankcases), heads, and
carburation or throttle body (stock venturi size), kickstarter or electric starter. Displacement determines the
class. OEM displacement specifications must remain
stock.
b. GASOLINE ONLY

3. Production, Vintage (PV)
a. Same as 3.11L.1 but with a production date prior to 1956.
b. Allowable overbore in this class is + .050- inches over
OEM standard bore to remain in displacement class.
4. Production, Classic (PC)
a. Same as 3.11L.1 but with a production date prior to 1981.
b. Allowable overbore in this class is + .050- inches over
OEM standard bore to remain in displacement class.

But you could put a .050 bore on the stock size and remain in class...    Just saying...

[donpearsall]

4. Production, Classic (PC)
a. Same as 3.11L.1 but with a production date prior to 1981.
b. Allowable overbore in this class is + .050- inches over
OEM standard bore to remain in displacement class.

But you could put a .050 bore on the stock size and remain in class...    Just saying...

I have always wondered what that means. For instance, if your original stock class is 1000cc and your stock displacement is 999cc, but the .050" overbore increases the displacement to 1001cc, can you remain in the 1000cc class? For non-classic bikes you would have to go to the 1350cc class.
The wording is confusing.

Don

[roflhat]

Yeh that's what I'm reading too, it is the standard carb with standard venturi size so should be alright. Will try source another to take with me just in case

From what I understand of the displacement rules you can rebore up to .050" but have to remain in the displacement class. So if you've got an 89cc bike running in the 100cc class you can bump it up a bit, same as non classic bikes only you're allowed a larger re bore

[Stainless1]

Yeh that's what I'm reading too, it is the standard carb with standard venturi size so should be alright. Will try source another to take with me just in case

From what I understand of the displacement rules you can rebore up to .050" but have to remain in the displacement class. So if you've got an 89cc bike running in the 100cc class you can bump it up a bit, same as non classic bikes only you're allowed a larger re bore

Hopefully your carb work didn't change the venturi size... Mostly they are looking for folks that bored the carb larger than stock... more air, more fuel, more power

Actually in production vintage and classic you can exceed the class limit.  But only if you are working from stock bore +.050 cylinder recondition allowance.  If your motor was exactly 100cc and the .050 made it 105cc then you are legal.  You get the stock bore + the .050 in classic and vintage... no matter where it lands provided you were in class with stock bore and stroke. 
Take proof of stock specs...
Now don't take my word on it.... send an inquiry to the BMST and confirm it... before you bore... but that's the way I read it.
Its been years since I raced at the Bub, now BMST, but that's the way it looks.... Maybe the more recent participants will chime in with real life experience
 

[Chris V]

I've run the same 72 Yamaha in the classic 350 and been measured many timed by Drew and by Curtas. stock bore is 347 + .040 over makes it 358 if I'm calculating 
correctly somebody check it, and I've remained in 350 class

[Stainless1]

Chis, that's the number I get as well... So your 1mm overbore allows you to race in classic 350 even though you are 358cc.  That is pretty much the real life info roflhat needs. 
Thanks 

[roflhat]

Wow interesting, that's good to know. Currently still at the standard 98cc so potentially a bit more to be had there

[roflhat]

Reply from Drew regarding smoothing the carb entry, still not sure if it's allowed or not
"Hello,
As stated in the regulations: A "production motorcycle class" is "as produced by a recognized manufacturer".
The o.e.m. venturi size requirement has a definite mention in the rules.
However, if one was to be protested by another competitor they could run the risk of their component
being deemed NOT "as produced".
Best of luck with your build."

[Stainless1]

Well I guess the same could be applied to high compression pistons, big valves and head porting....