Valve stem end damage.

I've just been checking my tappets, and have found that the exhaust valve ends have worn in a very slightly dished (damaged) shape. The end of the valve has barely spread (less than 0.002"), but I'm just wondering what the likely cause is?

I have Steve Maney alloy barrels and his chrome molybdenum pushrods which have a lower rate of expansion than the standard pushrods. Also as the barrel is alloy and expands more than the cast iron barrel, and on Steve's advice, I have set the tappets cold to about 0.001" to 0.002" and when the engine warms up I end up with tappet gaps of about 0.011" I have checked the valve springs and they don't become coil bound.

I am thinking of popping some lash caps on the valve ends which have a wider surface area and hopefully are harder and wear better than the end of the valve stem, but just wondered if the engineers amongst us could enlighten me at all as to the most likely cause of the "dished" wear?

Unless the valve stem has a stelite tip the wear you describe is pretty norrmal.
I think you will find that a lash cap will wear just as fast as a plain valve but they are easily replaced when they do. Jim

Thanks for the re-assurance Jim. The lash caps that I have are 0.050" thick. Although best practice would be to reduce the valve stem by the same amount, will the extra 0.050" height on the valve stem be detrimental to the engine or affect significantly the power? I realise that the geometry will be slightly altered.

If the valve geometry is not quite right, and the rocker arm slides across the top of the valve more than usual can be partly the cause of this too.
Checking that your pushrods or valves are not too long, or short, may help here ?

Reggie said:

Thanks for the re-assurance Jim. The lash caps that I have are 0.050" thick. Although best practice would be to reduce the valve stem by the same amount, will the extra 0.050" height on the valve stem be detrimental to the engine or affect significantly the power? I realise that the geometry will be slightly altered.

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An extra .050 on the valve stem will be a good thing. I commonly go .050 to .100 longer when I am using a high lift cam. Jim
You may need to shorten the pushrods.

Jim wrote;

I commonly go .050 to .100 longer when I am using a high lift cam.

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Jim, is this to compensate for the greater total movement of the rocker arm and by starting it at a higher point keeps the geometry correct at the mid point :?: Or am I talking bo**ocks?

Reggie said:

Jim wrote;

I commonly go .050 to .100 longer when I am using a high lift cam.

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Jim, is this to compensate for the greater total movement of the rocker arm and by starting it at a higher point keeps the geometry correct at the mid point :?: Or am I talking bo**ocks?

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Yeas, that is basically what it amounts to although I didn't start doing this because I took measurements and figured it up.
I started doing it because I was using a readily available stelite tipped valve that was longer than stock. I hated to cut the stelite tip off and run a lash cap so I tried it as it was. I found that with the bigger cams over about .400 lift -the longer valve made a better wear pattern and lasted longer. Jim

OK, thanks JIm.

What's the issue to just adj lash to make up for wear? At what point does it become an issue? My bud Wes sure ain't bothered about his long suffering stems likely 40+k miles by now. As flat feeler blades straddle the groove, just measure by the thread count back off method. Peel ran hard caps and mushroom adjusters on K/W 6mm stems, that controlled valves beyond red line yet still showed about same wearing in and mushing of mushrooms.