Shim measuring question.

[droog]

Hello

I'm just wondering how you guys record your shim measurements assuming you are using a digital micrometer that measures to the third decimal place (thousandths).

Do you bother factoring in the third decimal place into your final measurement or do you just go with whatever the first three figures are?

For example -

A shim that measures from between 1.971mm to 1.975mm on the micrometer would be rounded down and recorded as a 1.97mm shim.

A shim that measures from between 1.976mm to 1.979mm on the micrometer would be rounded up and recorded as a 1.98mm shim.

Or would you just ignore the third decimal and record this as a 1.97mm shim?

Cheers for any advice.

[Nobby the Bastard]

Shims are thicker than 2mm.. I bet the three numbers you are looking at are just the numbers behind the decimal point and so are in thousandths.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[Campbell SOUP]

The shims for my F4i turned out to be thinner than 2mm so it is possible!

In relation to the OP's question, it depends really how accurate you want to be. My bike has a valve clearance tolerance band of ±0.03mm, so I could aim for the nominal value using my 0.01mm micrometer and be confident it would be within the tolerance band.

Some shims would read at 1.97mm, but knowing that shims were available in 0.025mm steps I recorded them as 1.975mm shims. Being a bucket-over-shim arrangement it was quite unlikely there would be any wear and could just go off the laser-etched markings, but it never hurts to be sure!

[droog]

Thanks for the replies!

Hi Campbell - yep - my bike is an F4i too so we are both working at 2mm and under.

[Campbell SOUP]

Yep, should be fine then!

To be really safe, once you've made your adjustments you can get your feeler gauge back out, and make sure that the minimum tolerance (backed up with micrometer measurement of the gauge) fits between camshaft and bucket, while the top tolerance doesn't. You won't know the exact measurement, but you'll know for sure you're within tolerance, and that's all that matters

[droog]

[Campbell SOUP]

Happy to help! Just been through the process myself, which took 3 weeks in the end after I a) put the camshafts back on incorrectly (misunderstanding the TDC mark on the crank) and b) ordered the wrong shims (bought bigger shims to loosen clearances... )

Many lessons have now been learned!

[Nobby the Bastard]

Some of us are used to having intake shims needing a gap of 0.015mm.....
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[droog]

[droog]

[steve the grease]

Generally in engineering metric measurements are given in Hundredths 1.11mm etc. In English/ the imperial system measurements are given in thousandths so 1.111"

There are 40 (39.37 actually) thousandths of an inch in a mm so a tenth of a mm is 4 thou (0.004") and a hundredth of a mm is 0.4 thou or less than half a thou. To measure to thousandths in metric is to go beyond the level of accuracy needed by most engineering applications and that humans achieve in a workshop, rather than laboratory, and therefore pointless.
____________________
All the above is my personal opinion, you can see my lips move, but I'm talking out of my arse.
I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of.....

[droog]

[MCN]

If there is a +- tollerance is to allow for inaccuracies in the tools used. And to allow for wear between services and adjustment intervals.
Set to specification. (Not to the tolerances.)
😉
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[droog]

[droog]

Hi

Just wondering if anyone has a view on the following:

I've got a couple of tight out of spec exhaust valve clearances which requires a shim sized at 1.83mm if I want to achieve my ideal mid-spec valve clearance measurement of 0.28mm

(Exhaust clearance factory spec: 0.25mm – 0.31mm)

As mentioned above - shims are sized in increments of 0.05mm and in the absence of a 1.83mm shim these are my options:

Fit a 1.85mm shim and get a tighter clearance than I was hoping for but which is in spec. I calculate that the 1.85mm shim will result in a clearance of 0.26mm

Fit a 1.80mm shim, and get a looser clearance than I was hoping for that is on the absolute upper limit of spec. I calculate that the 1.80mm shim will result in a clearance of 0.31mm

Just wondering if I should go on the looser or tighter side on this.

Thanks for any replies.

[Nobby the Bastard]

As they tighten over time go looser.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[steve the grease]

Yeah go looser, it's only a fraction. Tight clearances burn valve seats.
____________________
All the above is my personal opinion, you can see my lips move, but I'm talking out of my arse.
I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of.....

[droog]

Thanks for the replies - yes - looser sounds the way to go - cheers

[Pete.]

[Nobby the Bastard]

[MCN]