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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet Help Please!
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<blockquote data-quote="davidd" data-source="post: 24432" data-attributes="member: 1177"><p>I would just add a few comments to Howard's good advice. My experience with the timing gear endfloat is that you neet a wide selection of shims, regardless of the advice of Mr. Richardson or the Spares List. As long as your followers are hitting the cam correctly, you can shim the big and small idlers for best meshing and then endfloat.</p><p> </p><p>If you did not build the engine originally, I would not rely on the marks on the gears. Much like the timing cover, the gear wheels are interchangeable on twins and singles and as you may know, the rear cam in the twin is the cam in the Comet. The marks would be different in these applications, so many gears have marks on both sides and the gear was pressed on for the rear cam on the twin or the (front) cam on a Comet. In addition, the gear wheel could be pressed on randomly, making the markings useless. In general, it is best to check and see when the intake opens, if you know the cam spec.</p><p> </p><p>You are not correct about the timing marks being aligned on the compression stroke, although I would have thought the same as you. They are aligned on the exhaust stroke, more specifically, at 4 degrees BTD exhaust. This is what the illustration in Richardson's is showing. This is also where the intake and exhaust valves happen to be at exactly the same height. So, if you do not know what the cam is, it is best to set the cam based on this equal lift. As you may know, the marks on the gears only line up once and as the engine turns they will not line up on the next cycle, so you have to turn the engine backward if you are trying to use the marks when checking the valvle timing.</p><p> </p><p>Finally, it seems that you have a twin timing cover. The aft holes are generally not machined on a Comet. I would not hesitate to use the cover, but I would close up the aft holes. There may be others that have done this using perfectly good methods, but my preferred method is to circle the hole with a small punch until it is closed. It does not have to be oil tight, but it is nice to have the oil going where it is supposed to instead of flowing unrestricted into the timing chest and robbing your cam of its fair share of oil. I am otherwise not a fan of peening, but in this case it prevents the use of goop, discs, screws, etc., that may fall out and cause worse problems. On each cylinder, one hole supplies oil to the cam and one supplies oil to the cylinder. On the twin all four are machined on the Comet only the front two.</p><p> </p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 24432, member: 1177"] I would just add a few comments to Howard's good advice. My experience with the timing gear endfloat is that you neet a wide selection of shims, regardless of the advice of Mr. Richardson or the Spares List. As long as your followers are hitting the cam correctly, you can shim the big and small idlers for best meshing and then endfloat. If you did not build the engine originally, I would not rely on the marks on the gears. Much like the timing cover, the gear wheels are interchangeable on twins and singles and as you may know, the rear cam in the twin is the cam in the Comet. The marks would be different in these applications, so many gears have marks on both sides and the gear was pressed on for the rear cam on the twin or the (front) cam on a Comet. In addition, the gear wheel could be pressed on randomly, making the markings useless. In general, it is best to check and see when the intake opens, if you know the cam spec. You are not correct about the timing marks being aligned on the compression stroke, although I would have thought the same as you. They are aligned on the exhaust stroke, more specifically, at 4 degrees BTD exhaust. This is what the illustration in Richardson's is showing. This is also where the intake and exhaust valves happen to be at exactly the same height. So, if you do not know what the cam is, it is best to set the cam based on this equal lift. As you may know, the marks on the gears only line up once and as the engine turns they will not line up on the next cycle, so you have to turn the engine backward if you are trying to use the marks when checking the valvle timing. Finally, it seems that you have a twin timing cover. The aft holes are generally not machined on a Comet. I would not hesitate to use the cover, but I would close up the aft holes. There may be others that have done this using perfectly good methods, but my preferred method is to circle the hole with a small punch until it is closed. It does not have to be oil tight, but it is nice to have the oil going where it is supposed to instead of flowing unrestricted into the timing chest and robbing your cam of its fair share of oil. I am otherwise not a fan of peening, but in this case it prevents the use of goop, discs, screws, etc., that may fall out and cause worse problems. On each cylinder, one hole supplies oil to the cam and one supplies oil to the cylinder. On the twin all four are machined on the Comet only the front two. David [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Comet Help Please!
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