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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Series ‘C’ Comet Camshafts
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<blockquote data-quote="timetraveller" data-source="post: 104322" data-attributes="member: 456"><p>If you have two dial gauges use them both, one on the inlet and one on the exhaust valve. Ideally this means removing the oil tank. If you only have one dial gauge then do one valve after another but ensure that the degree plate cannot move while you are moving the gauge from one valve to the other. Find top dead centre by putting a stop down the plug hole and <strong><u>GENTLY</u></strong> turn the engine forwards and backwards taking a reading on the degree plate. Add the two values together and divide by two, re-centre the degree plate and then go back and check that you have top dead centre correctly indexed on the degree plate. If not, rotate the degree plate forwards or backwards a degree of two until you have it correct. Now start and take a measurement of the reading on the dial gauge every ten degrees of engine rotation. Before you do this nip up each tappet adjuster so that the dial gauge(s) move five to ten thou, lock up the tappet adjusters and re-zero the gauges. Write down on a piece of paper the engine rotation position and the dial gauge reading of the valve lift. Do this for several degrees before and after the cam lift has started and ended and at some stage watch the dial gauge while you rotate the engine so that the cam follower is tracing round the base circle. There should be no deflection larger than about one thou.</p><p> When you have finished this you will have a table with three columns. The first is the engine rotation position and the second is the lift for one of the valves. The third column is the lift of the other valve, inlet or exhaust. You can now type these figures into your spread sheet or send them to me and I will do it for you. It has taken longer to type this out than it takes to do it. If you do not wish to remove the oil tank then you can make these measurement from the top of the tappet adjuster but my advice is to remove the oil tank to do the job and while it is off the bike give it a really good clean inside. Unless it has been cleaned recently it might well have nearly seventy years of dirt and metallic particle in it which will need to be removed. You can make an inspection cap to fit into the top of the oil tank which makes the cleaning much easier but that is another project.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 104322, member: 456"] If you have two dial gauges use them both, one on the inlet and one on the exhaust valve. Ideally this means removing the oil tank. If you only have one dial gauge then do one valve after another but ensure that the degree plate cannot move while you are moving the gauge from one valve to the other. Find top dead centre by putting a stop down the plug hole and [B][U]GENTLY[/U][/B] turn the engine forwards and backwards taking a reading on the degree plate. Add the two values together and divide by two, re-centre the degree plate and then go back and check that you have top dead centre correctly indexed on the degree plate. If not, rotate the degree plate forwards or backwards a degree of two until you have it correct. Now start and take a measurement of the reading on the dial gauge every ten degrees of engine rotation. Before you do this nip up each tappet adjuster so that the dial gauge(s) move five to ten thou, lock up the tappet adjusters and re-zero the gauges. Write down on a piece of paper the engine rotation position and the dial gauge reading of the valve lift. Do this for several degrees before and after the cam lift has started and ended and at some stage watch the dial gauge while you rotate the engine so that the cam follower is tracing round the base circle. There should be no deflection larger than about one thou. When you have finished this you will have a table with three columns. The first is the engine rotation position and the second is the lift for one of the valves. The third column is the lift of the other valve, inlet or exhaust. You can now type these figures into your spread sheet or send them to me and I will do it for you. It has taken longer to type this out than it takes to do it. If you do not wish to remove the oil tank then you can make these measurement from the top of the tappet adjuster but my advice is to remove the oil tank to do the job and while it is off the bike give it a really good clean inside. Unless it has been cleaned recently it might well have nearly seventy years of dirt and metallic particle in it which will need to be removed. You can make an inspection cap to fit into the top of the oil tank which makes the cleaning much easier but that is another project. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Series ‘C’ Comet Camshafts
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