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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Partial Single Seizure? Safe to ride?
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<blockquote data-quote="royrobertson" data-source="post: 99478" data-attributes="member: 2486"><p>One thing worth checking is that the bore is absolutely square to the base flange. In my case, many years ago after a major blow-up, the new liners were bored "drunk". This made a race winning motor misfire and a very frustrated mid-field runner. As they had been done by a reputable re-bore company in Brighton it took me FOUR years to find the problem. It was only by reading Tuning for Speed again that put me on the right track. I "borrowed" a large steel bar from work and turned it between centres on my lathe until the barrels just slid on. One bore was 8 thou out of true and other 5 thou. The poor pistons were trying to go up the bore slightly sideways, the ring edges rounded and not sealing properly,</p><p>(Note 0.006-0.008 inch bore to piston clearance for racing on iron liners or for my Aptec plated 90 bore aluminium liners 0.003 inch)</p><p>To get racing again I just cleaned up the base flanges and the high sides of the liners and left the tops until later. With new rings fitted the performance was back.</p><p>I have checked and machined quite a few barrels over the years as this fault has been found even with original bores. Hopefully when I get the hang of it, I will be able to post a photo of my latest light weight mandrel soon.</p><p>Cheers Roy</p></blockquote><p></p>
[QUOTE="royrobertson, post: 99478, member: 2486"] One thing worth checking is that the bore is absolutely square to the base flange. In my case, many years ago after a major blow-up, the new liners were bored "drunk". This made a race winning motor misfire and a very frustrated mid-field runner. As they had been done by a reputable re-bore company in Brighton it took me FOUR years to find the problem. It was only by reading Tuning for Speed again that put me on the right track. I "borrowed" a large steel bar from work and turned it between centres on my lathe until the barrels just slid on. One bore was 8 thou out of true and other 5 thou. The poor pistons were trying to go up the bore slightly sideways, the ring edges rounded and not sealing properly, (Note 0.006-0.008 inch bore to piston clearance for racing on iron liners or for my Aptec plated 90 bore aluminium liners 0.003 inch) To get racing again I just cleaned up the base flanges and the high sides of the liners and left the tops until later. With new rings fitted the performance was back. I have checked and machined quite a few barrels over the years as this fault has been found even with original bores. Hopefully when I get the hang of it, I will be able to post a photo of my latest light weight mandrel soon. Cheers Roy [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Partial Single Seizure? Safe to ride?
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