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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Camshaft
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<blockquote data-quote="timetraveller" data-source="post: 105302" data-attributes="member: 456"><p>The way I did it was somewhat convoluted. Remember that not only am I not a cam designer, I am not even an engineer, just an astronomer. I started off with several criteria. The first was that I wanted a cam which gave good mid range power and peak power at 6,000 rpm. Secondly I wanted 0.45" lift, not about 0.36". Thirdly I wanted to do this with the acceleration of the valves never exceeding that of a Mk 2 cam. Forth, I wanted to design around a curved base follower as I had convinced myself that I could not get a symmetrical valve lift curve with the Vincent geometry and I wanted the symmetrical curve so that I could get a flat based acceleration curve. The extra lift was to be obtained by ratioed rockers, not on the cam itself as there are restrictions within the tappet covers. I used a spread sheet to get the curves shown above and then modelled the Vincent timing system in ACAD. Given that I then knew what I wanted from the spread sheet all I had to do was move the model of the curve based cam follower enough to move the pushrod the required amount and in the ACAD model drag the cam profile at one degree intervals up to meet it. The points around the cam were connected by a spline function to ensure a smooth and continuous surface. I did wonder about trying to make the cam a 'polydyne' but having measured the compression of the valve train by applying a lever to the outer end of the rocker it did not seem worthwhile. I also realised that although I could have designed for valve train compression at any one value for the revs it would not have been correct at others and this was meant to be a road cam, used over a wide range of revs, not a race cam to be kept in a restricted rev range. I had never realised that the maximum acceleration of the Vincent valve is equivalent to 200G. Hence the need for strong valve springs. I wanted to reduce that requirement.</p><p> I realise that to a professional cam designer this will seem a very amateur approach but we chaps who mess about at the bottom of the food chain just have to do the best that we can.</p><p>Thank you for taking the time to respond to these postings.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 105302, member: 456"] The way I did it was somewhat convoluted. Remember that not only am I not a cam designer, I am not even an engineer, just an astronomer. I started off with several criteria. The first was that I wanted a cam which gave good mid range power and peak power at 6,000 rpm. Secondly I wanted 0.45" lift, not about 0.36". Thirdly I wanted to do this with the acceleration of the valves never exceeding that of a Mk 2 cam. Forth, I wanted to design around a curved base follower as I had convinced myself that I could not get a symmetrical valve lift curve with the Vincent geometry and I wanted the symmetrical curve so that I could get a flat based acceleration curve. The extra lift was to be obtained by ratioed rockers, not on the cam itself as there are restrictions within the tappet covers. I used a spread sheet to get the curves shown above and then modelled the Vincent timing system in ACAD. Given that I then knew what I wanted from the spread sheet all I had to do was move the model of the curve based cam follower enough to move the pushrod the required amount and in the ACAD model drag the cam profile at one degree intervals up to meet it. The points around the cam were connected by a spline function to ensure a smooth and continuous surface. I did wonder about trying to make the cam a 'polydyne' but having measured the compression of the valve train by applying a lever to the outer end of the rocker it did not seem worthwhile. I also realised that although I could have designed for valve train compression at any one value for the revs it would not have been correct at others and this was meant to be a road cam, used over a wide range of revs, not a race cam to be kept in a restricted rev range. I had never realised that the maximum acceleration of the Vincent valve is equivalent to 200G. Hence the need for strong valve springs. I wanted to reduce that requirement. I realise that to a professional cam designer this will seem a very amateur approach but we chaps who mess about at the bottom of the food chain just have to do the best that we can. Thank you for taking the time to respond to these postings. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Camshaft
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