I thought I had a standard engine, 66 S3 Elan, having removed and stripped the head the camshafts have a single groove denoting SE specification. How can I confirm this? If they are SE spec, are the valve clearances the same as standard inlet 4-6 exhaust 6-8?
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Camshafts have a initial take up ramp that closes the valve clearance before accelerating to lift the valve. This take up ramp is typically about 10 thou in height on a twincam cam. If clearances get to great the follower and cam lobe contact during the high lift rate section of the cam lobe making the tapping noise you hear.
What valve clearance you need in a cold engine depends on a number of factors as it is hot clearance that matters. How much the head expands and how much the valve stem expands are the key factors in determining the needed cold clearance to keep the hot clearance in the 4 to 8 thou range.
if the valve material is changed the cold clearance can change as Lotus changed them between the early and late twin cams.
Race engines typically need a larger exhaust clearance as the exhaust valves can run hotter and close up the clearances, bronze or similar alloy valve guides help prevent this by cooling the valve better than cast iron guides
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