Valve shim retention in valve caps

Hi, wondering if anyone can throw some light on a problem I’m struggling to find answers to.
I’m currently building up the original 3.4 SE block and head for my XK140.
The head has been machined, new valve seat inserts and valve guides fitted, by a very experienced machine shop in the midlands who have a lot of experience in XK engines. I’m now doing the assembly.
I have new valves, springs, spring seats, collets and valve caps.
When I assemble these new parts into the head, I then give the valve stem tips a few decent taps with a hammer and brass drift to settle the collets in the caps. However some of the shims are only fitting into the caps by about 0.003-0.004". Given that the valve clearance on the exhaust cam is 0.006", this means that the shim has approx 0.002" space under it that could allow it to slip sideways in the tappet when the cam is on its base circle. This could cause a lot of damage. When setting the valve clearances on the bench, some of the shims can slip sideways off the valve stem tip unless held in place with oil/grease. The caps and collets are SNG Barratt.
If I substitute an old valve cap for the new one, using the same collets, the shim fits into the top by at least 0.009-0.010", thus holding the shim nicely in place. Anyone else had this issue? I could just use the original valve caps, but I have fitted valve stem oil seals so need the shorter modern cap to clear the seals.

Did you use chessman engineering for the machining Roger ? They are one of the few I trust to install new valve seats.
Something is not quite right (as you are aware) with your assembled new parts, I bought a second hand set of valve spring retainers etc from Ken Jenkins back in 2015 and didn’t have an issue with shims. There are a few items that can all add up to give you concern including new cam followers so it needs some careful thought and measurements. My gut reaction is the SNG items are not correct.
You might give Ken Jenkins a call?

What you are saying is that the new cam buckets are thicker (internally) than the old ones and so thinner shims are needed to get the same overall height and clearance.

New cam buckets may appear identically spec’d externally but that is not the whole story. For example, using some from an aj6/16 engine may have the same skirt length but they are much much lighter than those in a v12.

I suspect the reason to fit new ones comes down to whether the old ones were running concentrically in their bores and whilst the same basic spec remained for many years in many Jaguar engines, the detail changed.

Your mix and match components are subtly mismatched.

kind regards

This issue has been discussed in more depth in the xk section and on the UK E type forum…Steve Valve shims again, sorry

Hi all, it’s all sorted now - nothing to do with tappets or valve seat machining - it was a batch of spring retainers which were incorrectly machined for the collet tapers. I understand this has been addressed and the parts supplied now are fine. See threads as advised by Steve, above.