Tappet shims - minimum thickness

[quaybook]

Servicing the car recently I checked tappet clearances and found three of the inlets closed up to 4thou, and two of the exhausts at 12 thou, the rest within range. I'm surprised it is this way round because I would have expected valve seat recession to be greatest on the exhaust side, not the inlet.

However, removing the cams to reshim I've discovered that shim thicknesses are low (mostly in the 60thou range) so I guess I need new valve seats. So a head refurb is on the horizon but I want to continue to use the car this summer and would like to delay major work until the winter. However one of the inlet shims is 54 thou and will need to go down to 52 or 53 to get the clearances correct. This is well below the minimum standard shim thickness of 60thou. Will a 53 thou shim put the engine at risk? If so, is the risk that the shim might break up or is the danger that the collets come out because of reduced valvespring preload? If I use such a thin shim, should I keep max rpm down (5000?) until I can get the head refurbed?

Any advice would be most welcome.

Whilst on the subject, any comments on who to go to for the head refurb? The engine was last rebuilt (to sprint spec) by Kelvedon 25 years and 35000 miles ago, with new valves but cut not renewed seats.

Vernon

[AussieJohn]

If you use the thin ones make sure that the cam follower is sitting on the shim and not on the spring retainer.

[ardee_selby]

If so, is the risk that the shim might break up ...Vernon

This thread is worth a read wrt potential shim fractures and a workaround using thinner buckets:

elan-f15/valve-clearance-shims-less-than-060-t21286.html

Good Luck - Richard

[CBUEB1771]

As suggested previously the lightweight cam followers are thinner and could get you back into the normal shim range. I also seem to recall that Cosworth top-hat style shims are available down to 0.050" thickness, but memory may be failing me. A relatively quick fix that I have done is to remove the valves and surface the end of the valve stems down to get you back into the normal range of shim thicknesses. This requires great care to make sure the shim is only contacting the valve stem and not the valve spring retainer. Before disassembly you should be able to determine how much you can surface off of the valve stems before contact between the shim and spring retainer is probable.

[alexblack13]

I am sorry guys.. But... The minimum shim thickness should not be much below .060". If they are you need to rework the head with new seats and probably valves to suit. This assembly has a very hard and acutely stressed life. Even just considering the valves themselves. Think of the service life already undertaken and survived!! My rule of thumb, FWIW, is always this. If it were an Aircraft would you fly it? .......... Well, even if you were prepared to (and I wouldn't!)...You would not be allowed to.. !!!

The Cosworth shim blanks I used were .200" thick !! These were surfaced to thickness required for the Burton Cam's I used in the +2S130...

So.. To keep you going, and my advice would be quite gently.. NO track days etc unless you want to be completely rebuilding your engine, would be no thinner than .050".. And I personally would not grind the valve stems. That is a Bodge Royal.
If you are at the stage of being forced to grind the stems to use .050"+ shims then you need to rebuild the head.

Your choice but when set up and running ok make your red line 5K.....

Perhaps Rohan would comment?

Great weather up here right now... Hope you are enjoying the same.

Alex...

[quaybook]

Thanks all for your advice. Rather than use a thin shim and worry a lot I've ordered a lightweight bucket from QED as a temporary fix. I'll get the head re-seated this winter.

The weather is glorious here Alex. I was hoping to take the Elan to Castle Combe for the Club Lotus Trackday this Saturday but it looks as if I'll have to go in the tin top or the Westfield 7 if my dear lady can be convinced that a 220 mile round trip behind an aeroscreen is fun. I may well be in the tin top.

Thanks again guys, your speedy help much appreciated.

Vernon