Shim sizes


Full member
Punto GT
I'm really confused about this but how do I know wot size shim to use on my punto gt, my mechanic tells me I only have one correct but how did he find this out, please help

many thanx Dan
if you know some one who owns a mechanic business, or works for one, phone up SC MOTORS, tell them the registration, and they can tell you what you need on any part of the car, just by using the car reg.
Dan Dan Dan, hows the car going? You bought the Spax RSX off me a long while ago now :bigsmile:

0.4 inlet and 0.5 on the exhaust (+-0.05 tolerance) is what you're aiming for as the gap between the cam lobe and shim.

So, if you have a gap of say 0.5 on one of the inlet valves, and the shim on this valve is 3.0 (for examples sake) you need a shim of 3.1 to bring the gap down to 0.4. Understand?

You will have to work out what you need for all 8 shims. Then buy the closest size up and get them machined to suit. Re-shimming is a massive ballache tbh.

Unless it's not a standard cam? If not you will have to get the clearences off the manufacturer of said cam and use those, but the same principle still applies.
Are you referring to tappet shims ? There's plenty of shims in a car, in gearboxes, engines etc.
If it's the engine ones, you need to work out which ones by measuring your current clearances with a set of feeler gauges, take measurements and use the correct replacements by their value [in mm/thou, not £'s :bigsmile:].
If this is the question you are asking i will do a quick write up on how to do it, unless there is already one available on the site.
One of the admin team will answer that question.
Thanx you guys, massive help, so all I gotta do is measure them when the cam lobes are fully lifted n just measure that gap, n if it's not correct I have to but a new shim that will make it the correct clearence?

Hey Kyle really sorry to hear about your 1.6, I've just put those coilovers on this wk lol well the front ones anyway, not sure wot to do about the rear ones becuz my standard springs are lower then the spax ones, wot happened to the alfa gt?? Havnt properly been inthe net in ages so I'm not up to date lol
Wrote it off :confused: There's pictures at the end of the thread linked in my sig. After an Integrale Evo but going to leave it until after Le Mans now I think.
Although i'm not converse with this particular engine, measuring for the correct shims is in theory the same for all shimmed engines. Some have shims on top, others have them below a follower, they are generally referred top as bucket and shims.
Take a measurement with good feeler gauges, not some tatty old bits of rust that have been hiding in the bottom of the tool box for six years.
This is done as mentioned earlier in the post, with the piston at T.D.C. [top dead centre, this is when the piston is at the highest point of it's travel] and the camshaft lobe is in an uppermost position in relation to the piston, which means that the particular valve is fully shut.
Take the measurement with a feeler gauge that slides into the gap with a good fit, you shouldn't be forcing a feeler into place but it shouldn't be sloppy. Think of a perfect hand in glove fit. You may need to use one or more feelers together to get the right measurement.
Write the measurement down and note the cylinder/valve. Remove the shim and measure it with a micrometer. Add the sum of the shim and the clearance taken with the feeler gauge. From that sum, subtract the specified clearance and that will give you the size of shim required to re-fit.
In some circumstances an exact shim is not available, these can be corrected but not in general for the home mechanic so i won't go into that right now. If the exact shim is not available, go for the one that leaves a slightly oversize clearance. A shim that is too tight will not allow the valve to close 100%, this allows gases to pass and can burn out a valve, lower compression pressure and basically be incorrect.
The first engine i shimmed was a Honda CBX1000 bike many years back, 24 valves and if i remember rightly, about 18 of them were rattling, oh the fun of it and it was a favour for a mate too.
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