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Author Topic: Motorcycle tech question.  (Read 2221 times)
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F-Head
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« 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 
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Stainless1
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« Reply #1 on: July 17, 2017, 06:49:26 PM »

SCTA event or BMST?
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Stainless
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F-Head
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« 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
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Frenchinjection
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« 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.
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F-Head
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« 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
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comet
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« 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
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Koncretekid
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« Reply #6 on: December 23, 2017, 09:54:32 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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Frenchinjection
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« Reply #7 on: December 28, 2017, 12:50:36 PM »

If it is in the A class then you can do pretty much what you like. 
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**RP**
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« Reply #8 on: January 04, 2018, 10:27:19 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.
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Ralph Pitlock
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