Twin Cam Valve Clearances

[Vanden Perre]

Hello,

Can somebody who knows what he/she is speaking about comment on the figures of the valve clearances I measured on my twin cam?
For information it is a standard road engine with standard cams.
Figures are in mm and in inches.
See attached Excel sheet.
Thanks.

Olivier.

[john.p.clegg]

Olivier

Have a look at

elan-f15/worth-the-effort-t14012.html

John

[Foxie]

Olivier

Have a look at

elan-f15/worth-the-effort-t14012.html

John

Yes, that's a good link. The only thing I can add is the the manual quotes a single clearance for inlet as 0.005 to 0.007, but for exhaust the clearance is 0.006 to 0.008 up to engine number 9951, and 0.009 to 0.011 for later engines.

Miles Wilkins mentions this difference in the section about Engine Assembly, but only quotes the larger clearance in his Specificatioms section.

I can't remember ever reading the reason for the difference, Anyone know

[rgh0]

The normal reason for the change would have been a change in exhaust valve material altering the temperature expansion coefficient and requiring a larger valve clearance when cold to get the correct clearance when hot

Cams have a gradual clearance take up ramp off the base circle that is normally around 10 thou in lift to gently bring the cam in contact with the follower without making a noise if the hot clearance is more than the clearance take up ramp then the cam contacts the follower during the next phase in the cam lift profile which is the rapid acceleration phase and this results in the clicking noise you get with excessive clearance.

But knowing Lotus the change could just have been they got it wrong in the manual for the first few engines and rather thanadmit a mistake and risk warranty claims they just changed the spec when they found the problem and pretended it was a running improvement. The larger later clearance spec works for most modern valve materials available and I would use it for all engines.

cheers
Rohan

[Vanden Perre]

All right, thanks!

It looks as if I better increase the clearance on cylinder 1 inlet side.
Now a few questions about how to do it?
Can I remove the inlet camshaft without removing the head?
To remove the camshaft can I just slacken the distribution chain and remove it from the sprocket?
Once I have removed the camshaft how to remove the tappet? There is nothing to pull it out of the bore, do I need a special tool?
How easy is it to realign the two timing marks on the sprocket? How accurate does this need to be? What is the height tolerance between the two marks? It looks difficult to align them properly when the engine is in the engine bay because of the radiator in from of the engine.
Any other advices?
Thanks for your help.

Olivier.

[AussieJohn]

The cam follower will come out with a magnet or two small screwdrivers, make sure the pistons are not at tdc when you rotate the cam also be carefull not to hit the valves with each other, best to loosen off the other cam while turning. cheers, John

[alexblack13]

Hi,
Don't you have a manual? It is advisable to get one and read up and understand b4 you start.

Answers.. Yes you can safely remove the cams. The followers can be removed with a hand valve grinder tool. The rubber sucker is pressed onto the follower and you simply lift it out. Make sure you carefully measure the clearances (COLD) and note them carefully. Place all components in order. Don't mix n match! When you have your adjustments made (I keep them a thou loose) reassemble the cams. Refer to manual.THE CAMS MUST BE IN THE CORRECT POSITION BEFORE CAREFULLY TIGHTNING DOWN THE CAPS. DO NOT ROTATE THE CAMS WITHOUT THE SPROCKETS FITTED AND CAREFULLY TIMED. Fit exh sprocket 1st. The alignment mark should not be far away. Carefully fit the inlet sprocket into the chain with the mark where it should be and fit the bolts to secure.Tension the chain. Carfully rotate the engine BY HAND one full turn and check the marks line up. If you feel ANY resistance when turning over by hand..STOP and check why. All ok? Turn the engine again till it's on TDC and check the sprocket marks line up. Recheck the valve clearances.

This job is fraught with danger if you don't know what you are doing. One mistake = Disaster....

Dont Mix up parts..DONT refit sprockers in wrong position / dowel hole on the cams. Make sure you turn over by HAND..GENTLY..For the 1st time. carefully note all the clearances etc b4 you strip anything. AND...Make sure engine is on TDC and the timing marks on the sprockets are lined up. Note HOW WELL they line up. Take a few pics.


Good Luck.I am sure some others will help you with tips n hints etc as you go. Think everything thro 1st. If in doubt STOP n ask. Go get a manual or Mr Wilkins book. (even better!)

[Fred Talmadge]

I'm very slowly putting my car back together and it occured to me that I could check my valve clearance with the head off the engine. Yes or No? If yes I'll still check them once I put the head on and probably a couple more time as it heat cycles.

[Foxie]

I'm very slowly putting my car back together and it occured to me that I could check my valve clearance with the head off the engine. Yes or No? If yes I'll still check them once I put the head on and probably a couple more time as it heat cycles.

Fred,

You might find it comfortable to check and set the clearances with the head off and on the bench, but bear in mind the cams will not be moving in synch, as there is now no timing chain. It might be difficult to position the cam in the optimum position as the valve spring forces may 'snap' it back/forward. You will need to remove one cam while checking and setting the other, as otherwise the opposing valves will interfere.

A final check with the head on is a good idea, and then after an initial run, but you will probably find that further checks after heat cycling will make very little difference and are superfluous.

Sean

[marode]

I am about to re-shim my +2S built in 1970. My question has been kind of discussed here before, but I am still confused about the different values of exhaust valve clearances listed in the workshop manual.

Olivier

The only thing I can add is the the manual quotes a single clearance for inlet as 0.005 to 0.007, but for exhaust the clearance is 0.006 to 0.008 up to engine number 9951, and 0.009 to 0.011 for later engines.
:

But knowing Lotus the change could just have been they got it wrong in the manual for the first few engines and rather thanadmit a mistake and risk warranty claims they just changed the spec when they found the problem and pretended it was a running improvement. The larger later clearance spec works for most modern valve materials available and I would use it for all engines.

cheers
Rohan

One point is I can?t read the no. on the engine and also I?m not sure if someone used a different head for engine rebuilt someday. I measured between 0.006 and 0.011.
If Rohan is right, should I set it between 0.009 and 0.011?

[andyelan]

Hi Everyone

Just a note to Fred and others. While you can set the valve clearances with the cylinder head on the bench, do be aware that they will close up (esp on cly. nos 1 and 4) when it's bolted down to the engine. You must re-check once the heads torqued down and be prepaired to reset them.

I have noticed lots of people here, when they check valve clearance for the first time on a car they've just bought, seem to find those on no. 1 cylinder tight. I suspect this is the most likley reason

Regards
Andy

[rgh0]

I am about to re-shim my +2S built in 1970. My question has been kind of discussed here before, but I am still confused about the different values of exhaust valve clearances listed in the workshop manual.


If Rohan is right, should I set it between 0.009 and 0.011?

Gee i sure hope I am right otherwise there are few engines with problems

But seriously - The .009 to .011 inch clearance setting will work for all engines. While you could use a smaller clearance such as the orginal Lotus .006 to .008 inch clearance setting there is no benefit in terms of engine life or performance and more risk in terms of valve seat wear or thermal expansion creating a zero clearance situation where you risk burning the exhaust valves if they are held slightly open and hot gas leaks past and overheats them.

cheers
Rohan

[prloz]

Hi,
Seems there was a change of exhaust valve material and Part No.
The Ford workshop manual states the later exhaust valves have Part No. B26E020 rolled on the valve stem.
Regards,
Peter.

[Foxie]

Hi Everyone
While you can set the valve clearances with the cylinder head on the bench, do be aware that they will close up (esp on cly. nos 1 and 4) when it's bolted down to the engine. You must re-check once the heads torqued down and be prepaired to reset them.
Andy

That's new to me, and interesting, I must check.

Is the amount the clearances close up any way constant/predictable, and could this adjustment be incorporated when setting clearances on the bench, maybe by tending towards the upper limit ?

[andyelan]

Hi There

The clearances I got were as follows:-

Head on bench
Cyl Ex In
1 10.0 5.5
2 10.0 6.0
3 10.0 6.0
4 10.5 5.0

Head bolted to engine
Cyl Ex In
1 6.0 2.0
2 8.0 5.0
3 9.0 5.0
4 9.0 4.0

I've no idea if the changes would be repeatable or not but, now I think about it, it might be worth making an attempt at setting them on the bench to figures larger than they should be. They still of course should be checked once the head is in place but it might be they'll close up to the correct values and that will save a job. If thay don't, well you're really no worse off.

Regards
Andy