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Author Topic: Motorcycle tech question.  (Read 3656 times)

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Offline F-Head

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Motorcycle tech question.
« on: July 17, 2017, 04:20:14 PM »
Two tech questions from a newbie please.

I plan to build a motorcycle in the pushrod engine class; M-PG or A-PG.

1. Can I use aftermarket or modified cases, cylinders and heads?
2. Can I alter the bore and stroke provided I stay within the class capacity limit?

Or would these changes require entry into the 'Modified' engine class A.
I know vintage pre 56 entries must use the original (or close) parts but am unclear about 56 on.
I've searched through the book but can't find the answer.

Thanks for any help, Ian 

Offline Stainless1

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Re: Motorcycle tech question.
« Reply #1 on: July 17, 2017, 06:49:26 PM »
SCTA event or BMST?
Stainless
Red Hat 228.039, 2001, 65ci, MSA Bockscar Lakester with a little N20 
MSA Bockscar Lakester #1000 my fastest mile 245 and change, 84 ci turbobusa motor... but Corey's 233 MPH H/BFL record is still 3MPH faster than mine.

Offline F-Head

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Re: Motorcycle tech question.
« Reply #2 on: July 17, 2017, 11:59:53 PM »
BMST but from reading both their rule books I thought the specs were the same?
All help appreciated, thanks. Ian

Offline Frenchinjection

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Re: Motorcycle tech question.
« Reply #3 on: July 18, 2017, 06:30:22 AM »
F-Head, our bike is APS-PBF 750.  It has billet head, rods, crank, block, gearbox, and cases.  It's still a pushrod.

Offline F-Head

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Re: Motorcycle tech question.
« Reply #4 on: July 18, 2017, 06:58:39 AM »
Thanks Frenchinjection.

Did you seek clarification or just go with the rule book?
And did you change the bore or stroke, or stay with standard?

Thanks, Ian

Offline comet

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Re: Motorcycle tech question.
« Reply #5 on: October 25, 2017, 01:57:38 AM »
How did you get on Ian?
I always assumed (dangerous thing to do) that the heads had to be as standard from the factory so I am curious to know the answer on this.

cheers
John

Offline Koncretekid

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Re: Motorcycle tech question.
« Reply #6 on: December 23, 2017, 08:54:32 AM »
Ian and John,
I was just perusing some older posts and noticed this one that never got fully answered.  I don't have my rulebook in front of me but the only restriction that I'm aware of is that you can't change the number of valves in the head.  The head on my 500/600cc APG and APS-PG has been highly modified and in the 500cc version, the bore and stroke have been changed to remain under the class limit.  So a Westlake 4 valve motor is legal because it was made with 4 valve head, but I don't believe I can put a Westlake 4 valve conversion on my BSA single.  A Triumph 750 twin should be legal with the very late model ('78?) 4 valve head but you'd want to confirm that with tech.  I have only run AMA events so am not sure about SCTA on this rule.
Tom
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Offline Frenchinjection

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Re: Motorcycle tech question.
« Reply #7 on: December 28, 2017, 11:50:36 AM »
If it is in the A class then you can do pretty much what you like. 

Offline **RP**

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Re: Motorcycle tech question.
« Reply #8 on: January 04, 2018, 09:27:19 AM »
SCTA allows 8 valve head on a Triumph in M or A frame - pushrod engine since it was a production head on one model one year.  At least a few records were set with them in the past.
Ralph Pitlock
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Offline F-Head

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Re: Motorcycle tech question.
« Reply #9 on: October 17, 2019, 11:18:56 AM »
Hi all, I have not been on the forum for a while but I am back in the game now. I got clarification that I can run the Weslake even though they never made a production 5000cc road bike. It will therefore be in the Special rather than Modified class. I must obviously stick to 500cc and 8 valves are OK.
A very well-known specialist built me a motor but they couldn?t get if to run properly. I then took it elsewhere and now have it back. It is in a caf?-racer chassis for test purposes. I need to make some exhausts and then trial it in a few Straightliners events here in the UK. If it shows potential, I will then build a better chassis and target Bonneville. Thanks for your help with this.

Offline panic

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Re: Motorcycle tech question.
« Reply #10 on: October 18, 2019, 09:22:31 AM »
built me a motor

More details, please?

Offline F-Head

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Re: Motorcycle tech question.
« Reply #11 on: October 18, 2019, 11:00:44 AM »
I decided I wanted to build a period correct (not vintage class) 500cc Weslake. The 'expert' collected the parts, built the motor but couldn't get it to rev above 4000 rpm (yes I know). I then came across a 500cc short circuit motor with a known history from a retired racer but in need of a rebuild.
Now I have two properly rebuilt motors, the second as a spare, and I need some dyno time. I'm not kidding myself it will be a LSR record breaker but it should be good fun and  might also suit some other classes of event; hill climb, sprinting, etc. It's a hobby.  :-)