Exhaust Valve Shims

[MLCstag]

Sorry to repeat a topic that comes up often, but I've been looking at the valve clearances on the LH head due to an irritating ticking near cylinder 6. I know it can be 'typical' especially for a Mk1 but worthy of an inspection.

So, cover and cam are off after initially checking clearances. Buckets and shims out, cleaned and measured. I had noted an increased clearance on No.6 exhaust by 3 thou since last checking which I consider odd. The reason for starting this post however, is to raise a question about Exhaust valves over Inlet and whether exhaust are more prone to increased valve stem force? The photo shows the Exhaust shim and Inlet shim and it is very evident on all my LH exhaust shims that the wear is higher. Is this because of increased force, greater clearances or any other suggestions?

I have initially measured the shims (picking up a micrometer tomorrow for an accurate measurement) and it looks like three exhaust and one inlet will need to be replaced to reduce valve clearance to within specification and hopefully eliminate the tapping noise. The buckets show slight signs of wear but are generally still linear along their sides so I will be reusing them.

Would anybody reading this have any spare shims lying around? I estimate that I will need 4 in all as three exhaust and one inlet are under sized. The rest I will invert.

Happy New Year.

[flying farmer]

Can't say I have ever noticed a difference in wear rates, but then I have never really looked.
If the exhausts are more prone to wear the main reasons I could think of is greater valve stem to guide clearance when cold to allow for the extra expansion of the hotter exhaust. This would allow more sideways shuffling of the valve stem on the shim until the engine is hot.
Also the exhaust is hotter so will thin the oil between the stem and the shim, and finally the greater valve clearance will mean a faster initial acceleration of the valve as it will be further up the quietening ramp at the bottom of the lobe.

I think temperature is probably the most significant factor here.

I would aim for the tighter end of the clearance specified to allow for greater future wear, and wouldn't be bothered if it was a couple of thou too tight as the fast road cams I am using only use a 10 thou clearance on the exhausts and that has never given any problems.

Non of this might make any difference to the tapping however!
Neil

[marshman]

Have you tried rocking the buckets in the head? I recently checked the head on my Dolly Sprint as it was a bit too noisy - quite a lot of loud knocking/tapping. I found both the cam buckets on No. 4 inlet ( 16 valve head) rocked a lot in the head. On examination the buckets didn't look too worn and still measured round. But on replacing with some "good spares" from a Stag head rebuild they did not rock at all, this showing the originals were quite worn. This greatly reduced the knocking/tapping, far more than getting the valve clearances correct. and there were some quite wide clearances! Well worth checking in my opinion.

As Neil says aim on the tight side for valve clearances, a bit counter intuitive for me as you would expect some wear of the valve seat to close the gaps up but I have never found this to be the case.

Roger

[JeffW]

Over the holidays I checked and changed many of my shims and all the buckets on the LH head as well due to noise.

The buckets seemed to be ok with only a tiny bit of movement, but when I fit new ones from LD Parts, there was a substantial difference in fit and I had to be precise when installing them as the size was so exact. If the bucket was minutely off kilter it would not slide down.

I then had to do a lot of shim checking and changing and followed previous advice on here (and as Neil said above) went tighter on clearances to allow for both future wear and run in. After just a short run mine were 2 thou larger. However now I have a very quiet LH head.

I did not notice any specific wear differences in inlet and exhaust shims, but did not look closely.

Jeff

[mjheathcote]

If you do have an odd ticking noise check the exhaust manifold.
I know the cast iron manifold doesn't have a gasket, but I had a tick with my tubular manifolds and it was a weaping gasket, a little tweek of the setscrew and noise gone!

[Seaking]

Sorry to repeat a topic that comes up often, but I've been looking at the valve clearances on the LH head due to an irritating ticking near cylinder 6. I know it can be 'typical' especially for a Mk1 but worthy of an inspection.

So, cover and cam are off after initially checking clearances. Buckets and shims out, cleaned and measured. I had noted an increased clearance on No.6 exhaust by 3 thou since last checking which I consider odd. The reason for starting this post however, is to raise a question about Exhaust valves over Inlet and whether exhaust are more prone to increased valve stem force? The photo shows the Exhaust shim and Inlet shim and it is very evident on all my LH exhaust shims that the wear is higher. Is this because of increased force, greater clearances or any other suggestions?

I have initially measured the shims (picking up a micrometer tomorrow for an accurate measurement) and it looks like three exhaust and one inlet will need to be replaced to reduce valve clearance to within specification and hopefully eliminate the tapping noise. The buckets show slight signs of wear but are generally still linear along their sides so I will be reusing them.

Would anybody reading this have any spare shims lying around? I estimate that I will need 4 in all as three exhaust and one inlet are under sized. The rest I will invert.

Happy New Year.

Try www.qedmotorsport.co.uk lotus twin cam valve shim various sizes.


CAMSHAFTS AND FOLLOWERS
VALVE SHIM, VARIOUS SIZES
Cheers Glenn

[MLCstag]

Thanks Gents,

I'm perhaps not as hopeful now about eliminating the noise through clearances and think I'll try the fit of the buckets back in the head with a view to changing them. I'll also check for exhaust manifold leaks and tighten up the gaps to the lower limits.

I must say that the wear difference is so noticeable as the exhaust shims are highly polished.

[marshman]

Robsport also have them and they a fractionally cheaper at £2.16 each (inc VAT) if you use a discount code to get 10% off. Used them recently for a few for my Sprint. Next day delivery and only £2.24 postage.

[JeffW]

If you do have an odd ticking noise check the exhaust manifold.
I know the cast iron manifold doesn't have a gasket, but I had a tick with my tubular manifolds and it was a weaping gasket, a little tweek of the setscrew and noise gone!

I had this too - sounds exactly like cam bucket / tappet noise inside the car! Very good tip.

Jeff