Lotus Elan

Camshaft recognition

PostPost by: sepans » Fri Aug 11, 2017 7:14 pm

Hi,
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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PostPost by: nigelrbfurness » Sun Aug 13, 2017 8:24 am

Unless your car has never had a cylinder head overhaul, you should be looking at around 7-10 thou clearance for both inlet and exhaust. The critical factor is the valve material and this has changed over the years. Other people will no doubt be able to give you a fuller explanation! But as far as I am aware, the camshaft spec has little or no bearing on the valve clearances.
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PostPost by: rgh0 » Tue Aug 15, 2017 7:26 am

Measure the lobe lift - it should be 0.35 inch and the base circle to see if its the standard in the manual for an SE ( I am not at home and cant remember the number of the top of my head ). If all that checks out and they have a single groove and no other numbers stamped on it ( just the casting number on the cam ) then you probably have a SE cam. You really need to measure the duration also to confirm its an SE cam but that is not easy to do and you really need to take it to a cam grinder and get them to measure it up

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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