Valve Shims

[Ianashdown57]

Hi,
I have just bought a stock of used valve shims on ebay and find that some of them have numbers on them. So far the range is 16-56. These numbers do not seem to relate to the thickness of the shims in either metric or imperial and I wonder if anyone knows what they refer to or if there is a chart or something with the number and corresponding thickness.

I'm going through them all and cleaning and measuring them and will be filing them away in a small parts drawer set in order of size so this information isn't criticat, I was just curious.

Thanks,

Ian

[types26/36]

As far as I remember Lotus supplied shims from 0.060? to 0.120? although thinner and thicker ones are available, I have seen quite a few over 0.100" that were only etched with the the last two numbers example: your 16 would be 0.116 and the 56 would be 0.156?
Many have no numbers at all and it is always best to check the size even with numbered ones.

[billwill]

>it is always best to check the size even with numbered ones.


Indeed because a previous person may have ground them thinner than their original size.

[elansprint71]

I believe that other manufacturers also used the same diameter shims and they may have used code numbers. In the UK the Hillman Imp engine, for example used them. It's engine was born out of the Coventry Climax; others (I think) were the Lotus Esprit/Eclat motor, SAAB and some Triumphs, e.g. TR7.

[pereirac]

Don't you loose the surface hardening if you grind them down??

[69S4]

Don't you loose the surface hardening if you grind them down??

If you do it's taking a long time to show up. I've got a number of shims in my engine at the moment that were ground to size back in the 80's and have been in use ever since without anything untoward happening. I checked all the shims when the head was off for water pump replacement last summer and they're all still fine.

[oldelanman]

The numbers could be the last two digits of the Ford Finis code......16 = 0.090" and 56 = 0.113"

[reb53]

Don't you loose the surface hardening if you grind them down??

When doing mine a few months back I ran a portable hardness tester over them, and a bunch of my spares.
A good collection of ground and unground, worn, (dimpled), and unworn.

No discernible differences, which would lead me to believe that they are through hardened, not merely case hardened.
I think this would make sense from a manufacturing point of view as well.

Cheers,
Ralph.

[billwill]

Presumably you might soften them by overheating during grinding down.

[rgh0]

While I have never done hardness tests on ground shims I have certainly seen shims that are not through hardened. I have seen on a number of occassions the valve stem put a significant depression in the shim if its been ground on the face contacting the valve stem after a short period of operation.

If i grind shims ( which is rare now as i have a full stock of thicknesses) I only grind one side and then I make sure that side is on the top in contact with the shim pad on the cam follower where the compression stress due to its larger contact area is lower than on the valve stem contact on the other side.

cheers
Rohan

[richboyd]

One datum missing in this discussion: the shim diameter.
The shim must be slightly less than 16mm in diameter.

[types26/36]

The shim must be slightly less than 16mm in diameter.

5/8"

[alexblack13]

I once bought a stock of Cosworth .200" thick blanks especially for grinding to size. They were much smaller diameter and were machined to locate onto the top of the valve. You could then only grind them on one side. I used a nice little surface grinder with coolant. Sadly now long gone. I now have a little magnetic holder which I use with my belt linisher. Very fine grit though! Kinda polishes them to thickness. If (as Rohan says) you have a good stock of shims you should not need to alter them. I just take off a thou or two max. I always have a shim that's very close

Quite acceptable to gently grind to thickness required but do not put any heat into them. Any change in colour at all will ruin them IMHO....Keep them cool!!

Whilst we are at it. If you are at the stage of using shims much below .060" then it is time for new seats. Don't grind the tops off your valve stems either..Just my Humble, but I have seen this done. Bad practice and a bodge in my opinion.

Al'. .......

[alexblack13]

Should mention that the .200 thick blanks were for use with a set of re-profiled cams. From memory (Long time ago chaps) they were Burton BLL14 ?? or something like that...??

Can't remember for the life of me, but hey! Time is marching on...

Alex...

[oldelanman]

So Ian, did you come to any conclusions about the numbers on your shims ?