XJ6 4.2 valve shim question

Reinstalling std cams on my 4.2. No idea of real mileage. Replaced exhaust valves, lapped both inlet and exhaust. New springs, collets and seals.
Running rough and spotty variable compression was the catalyst.
Thinnest shim from Moss is 85 thou. Tried and still NO gap.
Please confirm my 3 options

  1. Grind shims. Sketchy
  2. Grind valve stem tops. Sketchy
  3. New seats and valves. Pricey.

Any thing i have.missed?

Valve shims under .085 are on EBAY: Jaguar valve adjusting shims C-2243 1948-1987 6 cylinder and all V12 engines | eBay However, if the shim is sitting on top of the valve and has some space before it sits on the shoulder of the keeper, then taking some off of the tip of the valve is most likely fine. This is not something you do with a bench grinder as the surface has to be perfectly flat and 90 degrees to the valve stem. Take off too much and the valves will need to be replaced. Also, if you use to thin of a shim and it sits to far below the shoulder of the keeper, then the tappet is not touching it and will cause noise each time the valve opens. Be careful. New seats and valves are nice if you have a machine shop that can install correctly and at the right depth.

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Questions arising, David - do you have no clearances on any valve, inlet or exhaust…??
Did you check valve clearances before dismantling - and with what result?
Nominally; valve seat recess may indeed cause no/insufficient clearances with standard shims - did you inspect? Even so, with new exhaust valves there should be adequate metal to get proper clearances there with standard shims…

Salient points are that shim thickness should be verified with a micrometer - particularly old or ground shims. And of course the computations and placing of the shims must be correct - it’s easy to go astray in a long and tedious process…

I suggest you first remove all shims - simply to verify the extent of the problem. Grinding shims or valve stems is an absolute last resort - both are surface hardened, and grinding will remove that. Replacing conditions require it… seats is of course prudent - but then only if their condition warrants it…

Running the engine with no or too little valve clearances is an absolute no-no, of course!

Malapropos; long time ago I encountered, on a friends car a misfiring cylinder. Took a long time to find that one cam was ‘ground round’ and looked like a bearing! No cam lift, but plenty of valve clearance…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)

A local engine/engineering machine workshop would be able grind either the valves, or shims.

I had this problem on my mk9 a few years ago and Ken Jenkins solved it for me.
He told me to replace the existing buckets with those from the later X300 which are a lightweight version and a direct fit. The difference being that the top part where the shim sits, is of a lesser thickness. This gives you plenty of room to fit a shim. The bucket part number is NAC2543AA and they cost £16 each back in 2019. The standard shim now be too thin, but oversize ones are available. I think they are the same as on some of the Rovers, or could easily be made up.
This method elimanates all sorts of dreadful bodge ups when someone tops too much off the valves or fits a shim that is too thin.

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