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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Checking the Cam timing on a twin
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<blockquote data-quote="timetraveller" data-source="post: 179552" data-attributes="member: 456"><p>First you need to get a degree plate, an index pointer to point at the degree plate and a piston stop. Then you can find top dead centre. You do this by rotating the engine,<strong> slowl</strong>y, up to the piston stop from each direction, halving the readings, adjusting the rotational position of the degree plate until you get exactly the same reading each side of the TDC position. Now remove the piston stop.</p><p>You will also need two dial gauges to fit over the top of the valve stems. If the engine is still in the frame (UFM) then you need to make up some method of measuring the lift on the top of the tappet adjuster. There was an item on here a few years back about making and extended pushrod which could sit in the cam follower hollow and have a flat on top which could move the dial gauge. That looked like a good idea to me. Whatever you do you need to be able to measure the lift of the valves, or pushrods, as the engine is rotated. Then rotate the engine in the forwards direction so that the inlet valve lifts, drops and closes. You will then be on the compression stroke. Keep rotating the engine. You should be able to see the exhaust valve closing and the inlet valve opening. When you have exactly the same lift on both valves the degree plate should read 4 deg BTDC. If it does not then you have to alter the valve timing so that you have the same lift on inlet and exhaust valve at 4 to 6 degrees BTDC. To do this you have to get access to the cam and valve gear inside the timing cover. That means taking off the timing cover, the steady plate and various other bits so that the cams can be rotated on the cylinder you are working on. One needs patience but there is nothing that requires an academic education or a brain the size of a minor planet. Just patience and concentration.</p><p>If all this seems like black magic to you then sit down quietly and think about how about a four stroke engine works. It will eventually become clear.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 179552, member: 456"] First you need to get a degree plate, an index pointer to point at the degree plate and a piston stop. Then you can find top dead centre. You do this by rotating the engine,[B] slowl[/B]y, up to the piston stop from each direction, halving the readings, adjusting the rotational position of the degree plate until you get exactly the same reading each side of the TDC position. Now remove the piston stop. You will also need two dial gauges to fit over the top of the valve stems. If the engine is still in the frame (UFM) then you need to make up some method of measuring the lift on the top of the tappet adjuster. There was an item on here a few years back about making and extended pushrod which could sit in the cam follower hollow and have a flat on top which could move the dial gauge. That looked like a good idea to me. Whatever you do you need to be able to measure the lift of the valves, or pushrods, as the engine is rotated. Then rotate the engine in the forwards direction so that the inlet valve lifts, drops and closes. You will then be on the compression stroke. Keep rotating the engine. You should be able to see the exhaust valve closing and the inlet valve opening. When you have exactly the same lift on both valves the degree plate should read 4 deg BTDC. If it does not then you have to alter the valve timing so that you have the same lift on inlet and exhaust valve at 4 to 6 degrees BTDC. To do this you have to get access to the cam and valve gear inside the timing cover. That means taking off the timing cover, the steady plate and various other bits so that the cams can be rotated on the cylinder you are working on. One needs patience but there is nothing that requires an academic education or a brain the size of a minor planet. Just patience and concentration. If all this seems like black magic to you then sit down quietly and think about how about a four stroke engine works. It will eventually become clear. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Checking the Cam timing on a twin
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