Lotus Elan and Lotus Elan Plus 2 Forums

Just a quick question as i'm about to fit my head.
I've read in a couple of places that the exhaust cam must be correctly timed before moving onto the inlet. I'm a bit confused as to why.
I'll be ordering offset dowels as required to get timing spot on, my question is why the exhaust has to be timed first?
Surely the position of the cam and crank sprockets is always related, the chain run is 'tight' between all 3 in the direction of rotation and only the cam position changes with dowels / vernier sprockets. In this case could i not determine correct dowel offsets for both inlet and exhaust at the same time avoiding the time delay of ordering separately for exhaust then inlet?

I expect this is due to the tensioner being on the inlet side of the timing chain, so the timing has to be right from crank > exhaust cam > inlet cam. I've had my timing chain on and off a heap recently and it seems natural to fit it in this order too.

Sounds like an old wive's tale to me! Often turns out to be the case when you ask "why" to lots of things! Make sure the chain is tensioned correctly, rotate the engine in it's normal direction. Once both cams are set rotate the engine a few times in the correct direction and then check both again to be sure.

The issue is not what order you time the cams but the order your connect the sprockets to the chain as others have observed. You need to make sure the chain is tight when fitting the sprockets and the cams positioned approximately correctly to ensure the offset dowels or adjustable sprockets can then bring the cams to the correct timing.

The chain needs to be slightly loose to actually get the sprockets on the end of the cam. I typically set the exhaust cam and sprocket with straight dowels at TDC position and back the crank off to be a little before TDC. Then I fit chain and exhaust sprocket. I then back the exhaust cam off until the chain to the crank is tight and then fit the inlet cam to the chain and tighten the adjuster. You can then take up the slack by rotating the crank to TDC and hopefully everything is right. in terms of chain and tooth relationships. Once you do it a few times you get a feel for how much slack you need to leave to make it all work easily

I then check the timing and determine what adjustable dowels or changes to adjustable sprockets are needed to advance or retard the two cams to get them precisely timed.

cheers
Rohan

Thanks all, makes sense about aligning the exhaust sprocket first. Looking forward to getting stuck into it, just awaiting valve springs.

I have found that when you are setting the timing and find you are a tooth out, try this: -

With the tensioner wound out, give hefty push down on the chain between the sprockets. This puts a lot of slack in the system and with a bit of judicious juggling you slip the sprocket off the cam (exhaust usually), pop the chain over a tooth and be able to push the sprocket back onto the cam (or perhaps my chain is worn..).

Jeremy