[chris_seven]

Tadd,

I guess that you mean what can also be described as a 'Top Hat Shim'.

We have been using these parts for many years on the Ford BDA , Lotus Twin Cam and Coventry Climax engines.

There are two techniques commonly used to make these parts:

Some suppliers sell batches of shims of a standard length with a 1.5-2.0 mm grinding allowance so that they can be selectively ground to suit a specific valve/tappet combinations.

Other suppliers sell them at varying lengths - typically in 0.001" increments between 60 thou to 0.25".

Both types are available in varying length combinations to suit different cam/carrier arrangements.
The recess to sit them over the valve is typically between 2.5 and 3.0mm.

The cost of these parts here in the UK is around $5.00 each for either style and there are many different ID and OD components available.

They are generally through hardened.

I thought, but may be wrong, that for DLC to successful the surface being coated had to polished - or certainly diamond lapped as a minimum.

I have just ordered a forging die as we are going to re-manufacture the early forged rocker but to work with an Elephant's foot adjuster (FIA regs for Period F cars do not allow Solid Rockers) and I discussed DLC finishing with Balinite but the cost of lapping on the rocker heel was prohibitive and we have decided to gas nitride instead.

I would also think that if you apply DLC then they will never wear but the rocker - which is much more expensive will wear and I would rather replace a lash cap than a 906 style rocker.

I would, however, like to know more about DLC if you have any good data.