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Crank build for racing engine
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<blockquote data-quote="davidd" data-source="post: 179215" data-attributes="member: 1177"><p>Greg,</p><p></p><p>That sounds about right. I think the Comet design is excellent, with its narrow crank and beefy design. Your high-compression alcohol engines may have contributed to a slightly earlier demise. David Tompkins has used this engine for five years. and won four national championships. That is normally about 12 races a year as they take the best of 10 finishes (which means you have to win ten races). If you pick an average of 100 miles per race, including two practice sessions per race to get correct gearing and tire pressures, that works out to 1200 miles/season. The rule we used was a rebuild around season three, which would fit John's 3,000-mile rule.</p><p></p><p>It comes down to how tight the cam spindle was when it was installed. That is the weak link in the reliability chain. The big end will probably last longer, but if you are running at a championship level, it is best to replace or rebuild it after three years. David has 6,000 or so on his engine. It is just a matter of how well the engine goes together and how much over-revving occurs. These engines are so reliable I could probably sacrifice some reliability for more power, but Dave always had the choice to switch to my cam, which has about 4 more HP, and he stayed with the MK2. I think this worked out well for him as a rider, so I have no complaints.</p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 179215, member: 1177"] Greg, That sounds about right. I think the Comet design is excellent, with its narrow crank and beefy design. Your high-compression alcohol engines may have contributed to a slightly earlier demise. David Tompkins has used this engine for five years. and won four national championships. That is normally about 12 races a year as they take the best of 10 finishes (which means you have to win ten races). If you pick an average of 100 miles per race, including two practice sessions per race to get correct gearing and tire pressures, that works out to 1200 miles/season. The rule we used was a rebuild around season three, which would fit John's 3,000-mile rule. It comes down to how tight the cam spindle was when it was installed. That is the weak link in the reliability chain. The big end will probably last longer, but if you are running at a championship level, it is best to replace or rebuild it after three years. David has 6,000 or so on his engine. It is just a matter of how well the engine goes together and how much over-revving occurs. These engines are so reliable I could probably sacrifice some reliability for more power, but Dave always had the choice to switch to my cam, which has about 4 more HP, and he stayed with the MK2. I think this worked out well for him as a rider, so I have no complaints. David [/QUOTE]
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Crank build for racing engine
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