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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
A.T.C. and timing magneto
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<blockquote data-quote="timetraveller" data-source="post: 16895" data-attributes="member: 456"><p>It sounds as though you have not done this before. If that is true then expect to have to be patient and do the job several times. You will have to check the timing as once the ATD is removed there is not a good way to ensure that the magneto does not rotate a little. Even if you clamp the magneto you will still find that there is a problem. What happens is that when you have everything in place and the timing carefully set (with the ATD temporarily set in the fully advanced position) and you then start to tighten the nut in the middle of the ATD you will get some rotation. There is a taper in the middle of the device which has to fit onto the tapered shaft of the magneto and in my experience even if you start to tighten by hand and then try to hit the end of the nut with a hammer to drive it onto the taper without rotation there will still be some movement. I expect to have to do it once or twice and find out how much the system is rotating and then do it again with the timing offset a little so that with the movement it ends up in the correct place.</p><p> </p><p>One other thing to consider is that modern fuels burn quicker than fuels did 60 years ago and most of us would now like to time the bikes with less advance than originally. If the new ATD has 19 or 20 degrees of movement, which gives 38 to 40 degrees on the engine then you will find that if you time it at, say, 36 degrees BTDC then it is slightly retarded for starting. Ideally we should now have ATDs with slightly less movement but most of us are compromising and using nearly the original figure, perhaps retarded to 36-37 degrees, which is a compromise between easy starting and the engine pinking when the throttle is opened quickly. Good luck.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 16895, member: 456"] It sounds as though you have not done this before. If that is true then expect to have to be patient and do the job several times. You will have to check the timing as once the ATD is removed there is not a good way to ensure that the magneto does not rotate a little. Even if you clamp the magneto you will still find that there is a problem. What happens is that when you have everything in place and the timing carefully set (with the ATD temporarily set in the fully advanced position) and you then start to tighten the nut in the middle of the ATD you will get some rotation. There is a taper in the middle of the device which has to fit onto the tapered shaft of the magneto and in my experience even if you start to tighten by hand and then try to hit the end of the nut with a hammer to drive it onto the taper without rotation there will still be some movement. I expect to have to do it once or twice and find out how much the system is rotating and then do it again with the timing offset a little so that with the movement it ends up in the correct place. One other thing to consider is that modern fuels burn quicker than fuels did 60 years ago and most of us would now like to time the bikes with less advance than originally. If the new ATD has 19 or 20 degrees of movement, which gives 38 to 40 degrees on the engine then you will find that if you time it at, say, 36 degrees BTDC then it is slightly retarded for starting. Ideally we should now have ATDs with slightly less movement but most of us are compromising and using nearly the original figure, perhaps retarded to 36-37 degrees, which is a compromise between easy starting and the engine pinking when the throttle is opened quickly. Good luck. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
A.T.C. and timing magneto
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