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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
New member, and comet question
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<blockquote data-quote="davidd" data-source="post: 94307" data-attributes="member: 1177"><p>James,</p><p></p><p>There have been many Comet owners that have seized their Comets very quickly. There are some major traps. One is to use recommended clearances that are often based on twins. The second is trying to get tight clearance in general when it will rarely produce beneficial results. If the rings fit properly you will rarely suffer from generous piston clearance in a single. </p><p></p><p>The single is different because it can build up heat quite quickly, compared to the twin, and that heat will be mostly in the piston. I think CP recommends .003" clearance in general for Vincents. That works fine for my Nicasil aluminum liner, but if I were using the stock Vincent liner I would go with .006" clearance. If you go with .003" it will likely seize as you ascend your first hill.</p><p></p><p>As for the amount of compression you want, it is based on what performance you are looking for. If you wish to go with the Mk2 cam I would go with a higher compression piston because the Mk2 when running looses a lot of compression, at least one point. On the other hand, the Mk1 or Mk3 will preserve most of the compression when running and will give you a higher running (or dynamic) compression ration than the Mk2. This is one of the reasons Mike 40m's bike starts so well when the Mk2 bikes can be balky.</p><p></p><p>If you want performance go with the Mk2 and the 8:1. Don't forget to check the cam and rocker clearances because the Mk2's will ruin your summer and your wallet if you don't check them.</p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 94307, member: 1177"] James, There have been many Comet owners that have seized their Comets very quickly. There are some major traps. One is to use recommended clearances that are often based on twins. The second is trying to get tight clearance in general when it will rarely produce beneficial results. If the rings fit properly you will rarely suffer from generous piston clearance in a single. The single is different because it can build up heat quite quickly, compared to the twin, and that heat will be mostly in the piston. I think CP recommends .003" clearance in general for Vincents. That works fine for my Nicasil aluminum liner, but if I were using the stock Vincent liner I would go with .006" clearance. If you go with .003" it will likely seize as you ascend your first hill. As for the amount of compression you want, it is based on what performance you are looking for. If you wish to go with the Mk2 cam I would go with a higher compression piston because the Mk2 when running looses a lot of compression, at least one point. On the other hand, the Mk1 or Mk3 will preserve most of the compression when running and will give you a higher running (or dynamic) compression ration than the Mk2. This is one of the reasons Mike 40m's bike starts so well when the Mk2 bikes can be balky. If you want performance go with the Mk2 and the 8:1. Don't forget to check the cam and rocker clearances because the Mk2's will ruin your summer and your wallet if you don't check them. David [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
New member, and comet question
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