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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Camshaft
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<blockquote data-quote="timetraveller" data-source="post: 105079" data-attributes="member: 456"><p>As a follow up to the above; oexing (Vic) sent me his rear short camshaft so that I could analyse it. This is an Andrews version of a Mk 2 The results are below. First I show the lift curves. These were taken from the ends of the valve stems.</p><p>[ATTACH=full]26176[/ATTACH]</p><p>Note that I set up the timing so that the cross over point is at about 4 deg BTDC as this seems to be a popular way of doing the timing. Nest I show the start and end of the inlet lift curve at higher magnification.</p><p>[ATTACH=full]26177[/ATTACH]</p><p>[ATTACH=full]26178[/ATTACH]</p><p>You will see that there is a quieting ramp at both the start and end of the lift curve. Vincent timing is taken at five thou lift and from these two curve we can see that Inlet opens about 60 deg BTDC and closes at about 65 deg ABDC. Five deg early for the start of the lift and three deg early for the end of the lift.</p><p>Below are the same data for the exhaust.</p><p>[ATTACH=full]26179[/ATTACH]</p><p>[ATTACH=full]26180[/ATTACH]</p><p> Once again there is a clear ramp at the start of the ex lift and a smaller one at the end of the lift. Timing is Ex opens at about 83 deg BBDC and closes at about 30 deg ATDC., Ten deg early and twenty deg early. If the cam was retarded by six degrees then the first of these three timing would be about right but that would put the cross over point at about two deg after TDC, not four degrees before.</p><p></p><p>Next I show the velocity graphs.</p><p>[ATTACH=full]26181[/ATTACH]</p><p>Note the little blip at the start of the inlet lift. The vertical scale is thous per engine degree.</p><p>Finally I show a smoothed acceleration curve. This was smoothed by taking running means of three points.</p><p>[ATTACH=full]26182[/ATTACH]</p><p> Note that now the vertical scale is thous per engine degree squared. For those of a metric persuasion </p><p> a reading of .00005 inches is 1.27 microns. My digital dial gauges have the fourth figure as either a zero or a five, that is they are only able to read to half a thou and so I cannot do any better than this. You will see how the quieting ramp at the start of the inlet lift shows up on the acceleration curve. The thing which is a pleasure to see it that the negative part of these curves, which is where the valve springs are doing their job, is approximately horizontal, never seen on standard Vincent cams.</p><p></p><p>The overlap is about 95 deg whereas the official Vincent figure for Mk 2 s is 105 deg. The value for a Mk 1 cam is only 68 to 75 degrees so these are certainly more Mk 2 than Mk 1.</p><p>Over to the experts.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 105079, member: 456"] As a follow up to the above; oexing (Vic) sent me his rear short camshaft so that I could analyse it. This is an Andrews version of a Mk 2 The results are below. First I show the lift curves. These were taken from the ends of the valve stems. [ATTACH type="full" alt="26176"]26176[/ATTACH] Note that I set up the timing so that the cross over point is at about 4 deg BTDC as this seems to be a popular way of doing the timing. Nest I show the start and end of the inlet lift curve at higher magnification. [ATTACH type="full" alt="26177"]26177[/ATTACH] [ATTACH type="full" alt="26178"]26178[/ATTACH] You will see that there is a quieting ramp at both the start and end of the lift curve. Vincent timing is taken at five thou lift and from these two curve we can see that Inlet opens about 60 deg BTDC and closes at about 65 deg ABDC. Five deg early for the start of the lift and three deg early for the end of the lift. Below are the same data for the exhaust. [ATTACH type="full" alt="26179"]26179[/ATTACH] [ATTACH type="full" alt="26180"]26180[/ATTACH] Once again there is a clear ramp at the start of the ex lift and a smaller one at the end of the lift. Timing is Ex opens at about 83 deg BBDC and closes at about 30 deg ATDC., Ten deg early and twenty deg early. If the cam was retarded by six degrees then the first of these three timing would be about right but that would put the cross over point at about two deg after TDC, not four degrees before. Next I show the velocity graphs. [ATTACH type="full" alt="26181"]26181[/ATTACH] Note the little blip at the start of the inlet lift. The vertical scale is thous per engine degree. Finally I show a smoothed acceleration curve. This was smoothed by taking running means of three points. [ATTACH type="full" alt="26182"]26182[/ATTACH] Note that now the vertical scale is thous per engine degree squared. For those of a metric persuasion a reading of .00005 inches is 1.27 microns. My digital dial gauges have the fourth figure as either a zero or a five, that is they are only able to read to half a thou and so I cannot do any better than this. You will see how the quieting ramp at the start of the inlet lift shows up on the acceleration curve. The thing which is a pleasure to see it that the negative part of these curves, which is where the valve springs are doing their job, is approximately horizontal, never seen on standard Vincent cams. The overlap is about 95 deg whereas the official Vincent figure for Mk 2 s is 105 deg. The value for a Mk 1 cam is only 68 to 75 degrees so these are certainly more Mk 2 than Mk 1. Over to the experts. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Camshaft
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