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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Cam timing -- again
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<blockquote data-quote="davidd" data-source="post: 84905" data-attributes="member: 1177"><p>I always find it difficult to compare Vincent cams as the seem to be measured at differing heights. The original Phil Irving calculations were measured at 0.005". The MegaCycle cams are measured at 0.050". Harley, and most others, measure their cams at 0.40". I think of a Mk1 as a 30-44-44-30 cam measured at 0.050". The Mk2 as a 37-51-51-37, also at the same height.</p><p></p><p>If you look at Martyn's first graph you can see easily that the cross-over or equal lift occurs just before TDC, which would be the vertical "0" axis. You can see that the equal lift (crossed lines) occur just before TDC at 4 degrees, or so. If you look down at the 3rd party Mk2 you can see that the crossover is nearer TDC (which can be moved), but what is most noticeable is that the graph lines show a lot of wobbling compared to the lovely Mk1 graph lines.</p><p></p><p>If you look at the wobbly lines where the valves are opening and closing you can see why you have to measure the cam at 0.050" instead of 0.05" on the lift scale. The exhaust has a lump right at 0.030". If you are trying to compare cams, you would like to stay away from the anomalies or they may skew your numbers.</p><p></p><p>When you use a cam machine you do not have a connecting rod or a piston.</p><p></p><p>[ATTACH=full]16937[/ATTACH] </p><p>As a result, you cannot set the degree wheel at TDC because you have no idea where that is. The best you can do is turn the cam until you get equal lift at both valves. You can then set the degree wheel at zero or 4 degrees before zero knowing that this cross-over point is now your only reference. </p><p></p><p>I think this machine is something Roy Robertson used to check cams.</p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 84905, member: 1177"] I always find it difficult to compare Vincent cams as the seem to be measured at differing heights. The original Phil Irving calculations were measured at 0.005". The MegaCycle cams are measured at 0.050". Harley, and most others, measure their cams at 0.40". I think of a Mk1 as a 30-44-44-30 cam measured at 0.050". The Mk2 as a 37-51-51-37, also at the same height. If you look at Martyn's first graph you can see easily that the cross-over or equal lift occurs just before TDC, which would be the vertical "0" axis. You can see that the equal lift (crossed lines) occur just before TDC at 4 degrees, or so. If you look down at the 3rd party Mk2 you can see that the crossover is nearer TDC (which can be moved), but what is most noticeable is that the graph lines show a lot of wobbling compared to the lovely Mk1 graph lines. If you look at the wobbly lines where the valves are opening and closing you can see why you have to measure the cam at 0.050" instead of 0.05" on the lift scale. The exhaust has a lump right at 0.030". If you are trying to compare cams, you would like to stay away from the anomalies or they may skew your numbers. When you use a cam machine you do not have a connecting rod or a piston. [ATTACH=full]16937[/ATTACH] As a result, you cannot set the degree wheel at TDC because you have no idea where that is. The best you can do is turn the cam until you get equal lift at both valves. You can then set the degree wheel at zero or 4 degrees before zero knowing that this cross-over point is now your only reference. I think this machine is something Roy Robertson used to check cams. David [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Cam timing -- again
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