Valve Shims

[rgh0]

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'. .......

These are called "top hat shims" and were a favored racing mod by Cosworth in the early years I guess because they are a little lighter being smaller in diameter and centered by the recess the valve stem sits in. The were also adopted due to use of a different retainer style that did not provide for centering of the standard shim as part of mods Cosworth did for a racing high lift valve train.

Thes days they are rarely needed or used in racing engines as far as i can tell as modern lightweight racing retainers make provision for the standard shim and any weight saving is insignificant compared to the hassle of having to grind them to suit from the .200 standard thickness they come in. Weight savings and spring design improvements in the rest of the valve train are now enabling reliable 0.5 inch lift and 9000 plus rpm operation within the standard spring pocket to cam centreline geometry which was not so readily achievable back in the Cosworth racing twin cam days.

cheers
Rohan

[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'. .......

These are called "top hat shims" and were a favored racing mod by Cosworth in the early years I guess because they are a little lighter being smaller in diameter and centered by the recess the valve stem sits in. The were also adopted due to use of a different retainer style that did not provide for centering of the standard shim as part of mods Cosworth did for a racing high lift valve train.

Thes days they are rarely needed or used in racing engines as far as i can tell as modern lightweight racing retainers make provision for the standard shim and any weight saving is insignificant compared to the hassle of having to grind them to suit from the .200 standard thickness they come in. Weight savings and spring design improvements in the rest of the valve train are now enabling reliable 0.5 inch lift and 9000 plus rpm operation within the standard spring pocket to cam centreline geometry which was not so readily achievable back in the Cosworth racing twin cam days.

cheers
Rohan

One of my friends up here who races an Elan nobbled the last of the tophats I had. He spotted them in my box and knew exactly what there were. He had been looking for some, so I was happy to give them to him.... Swopped me something for them though!!
Jim Grant.. Top man!!

Al' .....

LOL.... Thanks Rohan..

[Ianashdown57]

Hi Roger,

Not really! the number 56 was as listed in the parts listing as above, but that was the only one! I'm giving up on any reason and just cleaning and measuring every one and storing away in a small part drawer set I just bought for the job.

Thanks to all for all the suggestions.

Ian