The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Big Nick on 01.06. 2010 18:46
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This is my bed time reading
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page 2
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Thanks for taking the trouble to post these. Will print and read
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Thanks Nick, I have saved them. Good reading and is very similar to my favourite bed time stories. Tuning for speed by Phil Irving.
Cheers
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Cheers Nick, a real period piece.
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Reading this has reignited the old itch - balancing.
Eddie reckons 54% and 65% for racing.
I was recently talking to John Wood who won the British 250 historic championship in 93 and 94.
He ran a modified villiers and experimented with balance factors between 50% and 65%.
A few years ago, it blew up and he cobbled together an engine using bits and pieces he had lying around. His rider then asked for a tacho because there was so little vibration that he could not decide when to change gear and the race noise drowned the engine. When John finally stripped it down he checked the balance. It was 80% - way out side the range any one was using. He has rebuilt the motor carefully (at 80%) and this 250 single can hold 106 mph for 5 minutes with hardly any vibration between 6000 and 8000rpm.
Muskrat runs his A10 at 7500 rpm with a balance of 73%.
I know the revs are high, and one's a racer, and Muskrat probably snorts methanol for breakfast but both run smooth with a balance factor well above the accepted.
Muskrat, how does your motor behave at lower speeds?
Trevinoz said he had an atlas that was smooth running with balance factor at 70%.
It would be interesting to see how a bog standard A10 worked with 70%
Thats enough.. I'll get off the soap box .... for now, cheers
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G'day Olev,
It's a mine field, get it wrong, boom. Phil Irving recommended 66%. I tried that and it was good at 5-6000 so over the next couple of rebuilds I increased it till it was good at 7+. The flywheel was also lightened a couple of Lb's. This was all when it was an A7 on meths at 13:1. I only raced in Div 2 (poor guys) and was the first across the line at the NSW Champs at the Creek in '96, '97.
Now it's an A10 it feels most comfortable at 6-6500 = 100 mph. At 3200 = 60 mph it's not too bad, numb hands after about 30-45 minutes. At 30 mph I don't know, not there long enough. At idle the rear guard is like a pogo stick!!!
Different frames and fixings make a difference to vibes, I think my alloy engine plates help, but my over the top head steady hinders.
Balancing all the other bits ( rockers, valve keepers, etc ) is also very important.
After 2 weeks of rain the sun came out today. Short ride into town to warm up then 120 on way home. FUNNNN.
Cheers
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i think i have this artical,but with some extra bits,i,ll seek it out and try and copy it,