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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
ET35 to valve guide clearance
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<blockquote data-quote="timetraveller" data-source="post: 126538" data-attributes="member: 456"><p>There are two clearances to worry about. The valve head to the piston and the valve stem block (don't have the part numbers here) to the top of the valve guide. I rotate the engine so that the valve is on maximum lift and then, using a suitable lever under the tappet end make sure there is one tenth of an inch clearance. That checks the valve stem clearance.</p><p>To check the valve head to piston clearance by far the best way is plasticine on the piston cut out and turn the engine over a few times. This is a pain in the whatsit and requires a lot more dismantling which is inconvenient unless uo are doing that for some other reason. The alternative is to go back to the levering the rocker method and to consider where there is the minimum clearance. Note that the inlet valve is opening some time before TDC and the exhaust some time after. This is where patience comes in and you really need a plot of lift against engine rotation for about one hundred degrees about TDC. You will then see how much lift there is at TDC and you can go to TDC and do the lever trick.. The problem is that in many cases it is not the flat face of the valve head which touches the matching angle on the piston cut its but the very edge of the valve which just touched the edge of the cut out. Enough to make a mark but sometimes not enough to feel. I always cut back edges of those cut outs with a scraper unless it is the lowest compression ratio pistons.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 126538, member: 456"] There are two clearances to worry about. The valve head to the piston and the valve stem block (don't have the part numbers here) to the top of the valve guide. I rotate the engine so that the valve is on maximum lift and then, using a suitable lever under the tappet end make sure there is one tenth of an inch clearance. That checks the valve stem clearance. To check the valve head to piston clearance by far the best way is plasticine on the piston cut out and turn the engine over a few times. This is a pain in the whatsit and requires a lot more dismantling which is inconvenient unless uo are doing that for some other reason. The alternative is to go back to the levering the rocker method and to consider where there is the minimum clearance. Note that the inlet valve is opening some time before TDC and the exhaust some time after. This is where patience comes in and you really need a plot of lift against engine rotation for about one hundred degrees about TDC. You will then see how much lift there is at TDC and you can go to TDC and do the lever trick.. The problem is that in many cases it is not the flat face of the valve head which touches the matching angle on the piston cut its but the very edge of the valve which just touched the edge of the cut out. Enough to make a mark but sometimes not enough to feel. I always cut back edges of those cut outs with a scraper unless it is the lowest compression ratio pistons. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
ET35 to valve guide clearance
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