I was sensitized to the importance of having the cam at the proper position before setting clearance. Circa 58.
I built a "T’ speedster from junk. Well, not quite. Brand new 8 after market valves. Splurge !! A machine shop ground the seats in the block for me. Another splurge.
And, I lapped them for a cleaner seat. No adjustment here, other than grind the end of the valve to get the desired clearance. No getting back of an error. or, so i thought.
Yup. I screwed one up. Ground off too much !!! That “lobe” position thing…
So, I went to visit one of my clients. An old Ford mechanic, now with an independent shop. He admired the seat and and demonstrated it to the younger line mechanics in his shop.
Then came hs old tech skills. Lit up the Oxy torch and added just a touch of brass to the tip !! A whirl at a bench grinder, clean new metal available for the proper adjustment. As I recall, it took only a light grind to get the gap…
After some more time expired, I drove the T over his place to “show off”. It was admired as it ran so nicely… Even fired immediately on the starter…
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Or, to translate into Jaguar speak, Robin 0,001" = 0,0254 mm - so the difference between 0,012" and 0,016" is 0,0508 mm. Which is indeed the tolerance given in metric in the manuals…
However, working to such decimal precision with feeler gauges is rather pointless. And I suspect that the range of shim thicknesses is cruder than that - to avoid an unnecessary amount of shims. Long time ago I worked on a Lancia - and I vaguely ‘think’ the shims were in 0,025 mm increments. Which makes sense…?
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Indeed, David; lobe position is absolutely essential in setting valve clearances - TDC is just counterproductive froth in this context…
However, with in-car adjustments; when all actual clearances has be measured; the engine must(!) be set to correct TDC mark on the damper (dist rotor to #6 plug lead) before the cams are removed for shim replacements. And, that done, the cams must(!) be replaced in the correct position, using the cam setting tool…
Playing with the cam timing is sort of optional - but the TDC mark is still the required reference point for cam timing…
I probably should have expanded my answer to clarify, that on this forum, I cannot recall metric clearances being quoted, so if the OP wishes to have better feedback he would be better off using Imperial.
Perhaps he is European, maybe even French, doubt they use Imperial ( I could be wrong of course)
