Minimum Valve Shim Thickness

[Retroman]

Hi,

I have a problem with number 6 and 5 inlet valves in that they are tight .003 and .001 respectively.
On removing the cam and taking out the shims they are both .009.
So...to get back to original spec .004 I can get away with number 6 but will have to take the other shim down to .007 to get original spec .004
Clearly if I want to match them against all the others which are the current recommended spec of .006 I will have to take off even more.
With various grades of emery cloth and a glass plate at the ready what are your thoughts before I b....r things up
I am 'told' reducing them below .008 is an unspoken dark art not admitted by many!! but will the shim risk breaking up if I sand off a thou or so.
Appreciate that the real solution is to remove the head and have the vale seats replaced etc but was hoping to leave this particular task till the winter.
All suggestions welcome.
Nigel.

[mgcjag]

Hi Nigel...please put your car model and name in the signature area.....if you had done so i wouldnt have to ask what model you have....it does make a difference to tappet gaps.....you measured shim of .009 sounds strange..shim sizes start at 0.085in......Steve

[christopher storey]

Steve : I believe from an earlier post that it is a 1969 4.2, and so the shim sizes do not make sense at all. I wonder if Nigel is getting a decimal point error with
his shim measurements , and what he thinks is 9 thou is in fact 90 thou

In any event , it is hopeless trying to thin shims down, because they are so hardened that breaking through the hardening is as near impossible as can be . If in fact he has 90 thou, then an 85 or 86 thou should bring his clearances back up ( mind you for a 69 car he is right on the borderline of the cams which need 12 to 14 thou clearances )

[Retroman]

Hi Guys,

Humble and embarrassed apologies.

I was using a cheap micrometer and did not notice it only went up to 100ths until I borrowed a friends Aldi special which does go up to 1000ths and then the penny or in this case the shim dropped!!

I will buy one of my own and start again tomorrow.

On the plus side it looks like I will be well within the shim range.

At least I got the camshaft off without breaking or losing anything......yet.

I will update details re my car.

Best wishes,

Nigel.

[mgcjag]

What model do you have.....should your gaps be 4 an 6 th or 12-14th?....Steve

[abowie]

As stated you probably have the later cams on your car which means a much wider gap.

While using shims under the minimum thickness isn't ideal, if this is just a temporising measure until you get your valve seats redone it should be ok.

I wouldn't try doing this at home. You will be able to get custom shims made locally for under 5 quid each.

When posting, I find it's easier to describe things as "6 thou" rather than 0.006". Easier to understand and less prone to error.

[Retroman]

Hi Guys,

Thanks for all the advice.
Profile updated to prevent any confusion.
The plate states that the clearances are 4 thou inlet and 6 exhaust although the previous owner told me that he had increased the gap to 6thou inlet and 8 thou exhaust on the advice given on the JEC forum, although I cannot find it.
Based on my initial measurements I may just get away with this until the winter.
Strange all the other clearances are consistent and spot on.
Maybe no 5 and 6 inlets were two vigorously ground in.
Cheers,
Nigel.

[chrisfell]

The most important piece of advice I can give you is..... please get yourself an accurate micrometer. Not an Aldi special. Mine is second hand, and probably saw its original owner through a life long career as an engineer.

The minimum shim thickness is determined by the distance between the top of the valve stem and the valve collar. If the valve gap has reduced to the point that the minimum shim is still too large, this is a sign of valve seat recession. The only cure for this is a head rebuild with new seats.

Many years ago I was invited to sort through an independent Jaguar mechanic’s stock of valve shims, which contained many he’d made himself. What I found made me determined never to use him again, the box was full of roughly made shims, some of which were wedge shaped. I cannot say whether these particular examples had been recovered from vehicles he’d serviced, or not, but the fact they were in his box of shims worried me too much.

[mgcjag]

Hi Nigel.....I would actually check what cam you have fitted.....the change happened in 68 and its mentioned that yours is a 69........I also wouldn't set gaps to what a previous owner said....unless he had modifications made...simple to check your cams...look here.....Steve http://georgiajag.com/Documents/Camshafts.html
NB ensure that when refitting camshafts you torque them correctly......

[abowie]

Hi Nigel.....I would actually check what cam you have fitted

Good advice. I was trying to find that link for you...

[Retroman]

Hi Guys,

Thanks for all the good advice.

The purchase of an accurate micrometer was good advice and it will be a good investment.

My cams appear to be the old type as they are held to the sprockets by two bolts and do not have any grooves in them.

I have set the clearances to match the rest of the valves, 6 thou inlet and 8 thou exhaust, which is 2 thou wider than standard and will see how it goes.

With the timing and carbs now adjusted the engine is running as sweet as a nut but a little lean at higher revs.

May try slightly richer needles.

Thanks again for all the good advice.

Nigel.

[abowie]

May try slightly richer needles.

Excellent outcome and thanks for letting us know how it turned out.

WRT tuning the cars to tend to run relatively rich at idle; I set mine for 5% CO. Before you go changing needles it might be worth checking the tune. IMO a standard XK engine will run very well with the standard needles.

[Retroman]

Hi Andrew
Thanks for the advice re mixture,
Will leave the needles for now and let the engine settle for a few miles and may richen it up a little if the plugs look as if they need more fuel.
Now onto tracing the oil drips!
Thanks again.
Nigel

[abowie]

may richen it up a little if the plugs look as if they need more fuel.

Now onto tracing the oil drips!
Thanks again.
Nigel

Plug colour is not very helpful with lead free fuels. Having said that, if your plugs do look lean/pale with unleaded they probably are quite lean...

WRT oil leaks. This is the patented Lyons underfloor anticorrosion system. It's largely unstoppable...

[johnetype]

Hi Nigel.....I would actually check what cam you have fitted.....the change happened in 68 and its mentioned that yours is a 69........I also wouldn't set gaps to what a previous owner said....unless he had modifications made...simple to check your cams...look here.....Steve

Steve, this has come up before causing confusion, I think you'll find the change happened around Oct. '69.