shim size questions

[gbw]

Hello. I'm well into my first valve clearance check/adjustment. Quite fun actually. But now I'm at the place where I have to decide what shims to purchase and I hope you folks can give me a sanity check.

I've taken to calling the valves for each cylinder "in" and "out" for intake and exhaust.

1out, 2in, 3out and 4out are all in spec.

3in has a clearance of 0.10mm with a shim labled 2.8 which I measure as 2.83mm.
I think if I put a 2.9mm shim here my new clearance would be 0.04mm

Is that right?

I have three valves (1in, 2out, and 4in) with clearance below 0.03mm which is my smallest guage. I juggled some shims around and took the following measurments.

1in has clearance of 0.13 with a 2.66mm shim. If I use a 2.75mm shim I should be at 0.06mm clearance.

2out has clearance of 0.03mm with a 2.71mm shim, so if I use a 2.7mm shim my clearance should be 0.04mm

4in has clearance of 0.1 with a 2.71mm shim, so if I use a 2.75mm shim I should be at 0.06mm clearance.

So I should buy a 2.9, two 2.75, and a 2.7. I'll have left over a 2.82, a 2.78, a 2.84, and a 2.83.

Am I on the right track?

Thanks,
gbw

[BassCliff]

I thought there would be no math today

Hi Mr. gbw,

Generally, when you add shim height, subtract the same interval from your clearance, and vice versa (when you subtract shim height, add the same interval to the clearance).

My suggestions:

For the 3in valve with .10mm clearance, if you replace the 2.83mm shim with a 2.85mm shim, that should give you .08mm clearance. (I like to run towards the loose end of the range if I can.)

1in @ .13mm w/2.66mm shim: Install a 2.7mm shim to bring the clearance to .09mm, which is close enough since the clearances tend to tighten up over time. A 2.75mm shim here would bring the clearance to .04mm, which is in spec but towards the low end of the range. That means you may be changing this one again next time.

2out @ .03mm w/2.71mm shim: Install a 2.65mm shim to bring the clearance to .09mm.

4in @ .10mm w/2.71mm shim: Install a 2.75mm shim to bring the clearance to .06mm.

After replacing a shim, always spin the motor a few times and re-measure the clearance. I have found that sometimes the theoretical math doesn't agree with the practical application.

As you have noticed, not all markings on the shims are exact. Usually the oversized ones are marked with an 'x', i.e. 2.60x. You seem to have an excellent grasp of how to use your calipers to measure the shims and "fine tune" your clearances. Keep up the good work and keep us informed.

Thank you for your indulgence,

BassCliff

[gbw]

Apologies for the math

BassCliff - Thank you for the compliment and so much for your suggestions. I feel better about getting some of the shims down to 0.09mm and letting them wear into spec instead of setting them close to the bottom and having them wear out of spec.

As you have noticed, not all markings on the shims are exact. Usually the oversized ones are marked with an 'x', i.e. 2.60x.

Funny you should mention that. Of the 8 shims I'm working with:
three are unmarked
the 2.65x measures 2.70,
the 2.75 measures 2.79, and
the 2.65 measures 2.69

At first I thought my calipers were in error so I measured every one of my feeler gauges from 0.03 to 0.15...spot on.

All of these should really be marked one size larger than they are. Is that normal?

Thank you again for all your help.

gbw

[Guest]

At first I thought my calipers were in error so I measured every one of my feeler gauges from 0.03 to 0.15...spot on.

not really a confirmation of the accuracy of your calipers, as the range you tested is way from the thickness range of the shims...
you need to use a precise industrial standard micrometer to be 100%sure

anyhow, i'd just use the shims one size down from whats stamped on the existing shims (to start with) and check for the clearances again (as your feeler gauge would be an accurate tool)

you can possibly do this by swapping some of the shims you have (you do need an extra one to temporarily put in place while swapping the shims out)

to make things easier, you can email "steve" for a spreadsheet that calculates the shim sizes you need

[gbw]

not really a confirmation of the accuracy of your calipers, as the range you tested is way from the thickness range of the shims...
you need to use a precise industrial standard micrometer to be 100%sure

True...but it made me feel better And really, isn't it all about me feeling better???

to make things easier, you can email "steve" for a spreadsheet that calculates the shim sizes you need

Email sent...thanks for the suggestion.

[Guest]

let us know how it goes, we love gs success stories :-D

[Nessism]

I've noticed some variation in the shim thicknesses and use a micrometer to measure each one before installing. Have not noticed any that are mismarked, and I've got a pretty good sized pile. My guess is that your calipers are off a little if you are reading three different shims all thicker than marked.

Regarding the valve that seems to need a 2.90 shim, go back and check it again. I'd try your thickest shim and see if you can get the clearance down to 0.9mm which is fine.

Good luck.

[gbw]

My guess is that your calipers are off a little if you are reading three different shims all thicker than marked.

That is possible. Just something I bought at Home Depot for like $30. I might try to find a good micrometer but I thought the digital calipers would be fine.

I also have one shim marked 2.8 and the calipers measure 2.83.

I supposed it is possible that I'm introducing error into the measurement just by the way I'm holding the tool and part. I don't know.

Regarding the valve that seems to need a 2.90 shim, go back and check it again. I'd try your thickest shim and see if you can get the clearance down to 0.9mm which is fine.

Good luck.

I went back and rechecked everything. This being the first time I've done anything like this I'm sure I won't get it perfect the first time.

I spun the engine a couple of time and took new measurements of the gaps and shims. Everything was pretty similar the second time but I think I'm getting a better feel for gauges and shim clearance.

As it turns out I think 3in is at 0.09, not 0.10, so I'm not going to mess with it.

I've ordered new shims and I can't wait to how it all works out. Since several of my shims are not marked I based all my calculations for the new shims on the measured thickness of the shims. If my calipers are out of whack I'm in for a little disappointment when the new shims arrive.

I'm going to try to get my hands on a micrometer...now I'm curious and this is going to bug me all day.

This is actually quite fun, but very distracting from work.

Thanks!
gbw

[Guest]

gbw, I've been using a Mitutoyo and while it isn't a US Bureau of Standards primary instrument, it is pretty good. I'll bet yours is very consistent and repeatable just check to be sure it is zeroed as you make a measurement and afterward. Very few of the shims I've checked have been exactly as marked, even the new ones. They are usually .01 + or -. I've looked at something like 50 and I doubt that 10% are right on the money, but they are close enough to do the job. Ray

[tkent02]

gbw, I've been using a Mitutoyo and while it isn't a US Bureau of Standards primary instrument, it is pretty good. I'll bet yours is very consistent and repeatable just check to be sure it is zeroed as you make a measurement and afterward. Very few of the shims I've checked have been exactly as marked, even the new ones. They are usually .01 + or -. I've looked at something like 50 and I doubt that 10% are right on the money, but they are close enough to do the job. Ray

Also the old shims seem to be a little bit thicker in some areas, thinner in others.
Either worn funny or not made that precisely.