Landracing Forum
Tech Information => Technical Discussion => Topic started by: F-Head on July 17, 2017, 05:20:14 PM
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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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SCTA event or BMST?
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BMST but from reading both their rule books I thought the specs were the same?
All help appreciated, thanks. Ian
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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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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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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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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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If it is in the A class then you can do pretty much what you like.
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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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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.
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built me a motor
More details, please?
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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. :-)