classic motorcycle forum
Motorcycle Discussions => British Bikes => Topic started by: Tj501 on July 25, 2017, 12:32:17 PM
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I need to make a new head gasket for my side valve Raleigh but have no idea what clearance I should run between top of piston and the head. Piston is a flat top and the head is also flat part way over the piston. 3mm copper would give me 0.5mm clearance. Is this enough?
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stick a bit of plasticine to the piston, turn it over and you'll see how much clearance you have to play with.
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0.5 mm (20 thou) isn't much, but provided it doesn't touch... This is the concept of "squish", pioneered by Harry Riccardo and later used to great effect by Franklin at Indian. The plan was to force most of the combustion gases into the valve chamber at TDC, to maximise volumetric efficiency, which was never too flash on a side valve.
Leon
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all the side valve Raleighs I ever had, about 4, had fixed heads.
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3mm copper would give me 0.5mm clearance. Is this enough?
Does that mean the piston protrudes up proud/into the head by 2.5 mm ?
That seems unusual ? Correct piston fitted ?
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That's correct - the piston does protrude past the top of the cylinder. It's the original crank, rod and piston so I can only assume it was designed this way. There was no spacer under the cylinder when it was dismantled......
I have a '31 motor which is fixed head to answer the other question.
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Hi,
It would be a better solution to fit a plate under the cylinder and use a thin (er ) head gasket
John