Lotus Elan

camshaft timing

PostPost by: potleyu18 » Sun May 26, 2019 3:55 pm

Having problems in getting this vital procedure right.

Set both cams so both inlet and exhaust lobes are facing each other on number four tappets and then set dial gauges on number one for TDC then following Miles instructions rotated the engine to get a reading when the exhaust tappet start to depress from there on any reading i get are no where near what according to Miles i should have.
Cams are Piper 285 with vernier adjustable sprockets

Is there any one who has done this and can help or is there a You Tube video out there.


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PostPost by: nmauduit » Sun May 26, 2019 5:20 pm

I'm not sure what procedure you follow, but the principle is to start from finding out precisely TDC, that is the reference point for setting the cam timing. Since the piston go twice to the top per cranckshaft revolution, looking at the lobes is for finding out which of these is the TDC is the one to be used as timing reference (the TDC of the combustion is done with both valves closed, obviously, so far from the timing zone).

I suppose you have a 360 degrees dial attached to the cranckshaft. One usually set itso that 0 corresponds to the TDC described above. Then in order to do the timing, one needs to rotate the crank a number of times (I usually only rotates in the conventional rotation direction, CW facing the engine, so that the chain stays under tension like it would under operation). Under the same principle one usually sets exhaust timing, which will not be altered when setting the inlet as it is directly under cranck tension. When done I usually double check timing, again only turning the cranck like under operation, to be sure. Then one still has to set the dizzy timnig.

hope that is not confusing... good luck !
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PostPost by: Craven » Sun May 26, 2019 6:55 pm

If the procedure you are following is to time using degrees before BDC ( 66 deg )when exhaust valves starts to open then forget it! use peak lift instead (inlet 107 deg After TDC). Reason being, degrees before BDC figure is with a stated the tappet clearance, so you would need to set your clearance to the stated figure, on a Twincam is a PITA.
This type of timing is usually done with deg before TDC on the inlet valve.
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PostPost by: vincereynard » Mon May 27, 2019 5:06 pm

+1 for Craven.

I timed by using Max. Open Position (MOP), which for the BV engine was / is 110 after tdc -

Establish true TDC. Then fix degree wheel with pointer. With a dial guage on No1 cam follower establish the point where the valve is fully open. You may have to do this a few times.

Compare with what it should be . This will give a figure of how accurate your timing is.

Remember that as the chain stretches the timing retards slightly. So a degree or (max) 2 advance is not necessarilly a bad thing. (Depending on clearance etc.)

Its a lot of faffing but ultimately rewarding.

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PostPost by: jono » Mon May 27, 2019 7:01 pm

..and its well worth the effort making up a mounting plate for the DTI
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