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Offline cat10

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Measuring Valve Clearance (Tips)
« on: March 10, 2020, 10:42:47 PM »
Hi folks, any tips on how to measure valve clearances accurately.
I find it quite difficult to get exact measurements of the valve clearances, I have tried using all sorts of feeler gauges.
Is there a preferred set of feeler gauges that makes measuring easier and more reliable. 

Offline tigerman1960

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Re: Measuring Valve Clearance (Tips)
« Reply #1 on: March 11, 2020, 07:07:22 AM »
A mate of mine bought me a very long set on e bay, I have had to bend them quite considerably to get them in, but they work very well with some patience and a few cups of tea  :002:
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Offline Paulhere

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Re: Measuring Valve Clearance (Tips)
« Reply #2 on: March 11, 2020, 07:47:48 AM »

Get a set that separate so you're just using the one feeler at a time not got the bunch in your hand. Bend the ends to ease access. Get the sizes lined up & note the actual gap on a sheet with pistons & valves drawn on.
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Offline awjdthumper

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Re: Measuring Valve Clearance (Tips)
« Reply #3 on: March 11, 2020, 08:54:07 AM »
Fortunately, I will not need to check my 12k valve clearances till the end of the year but I expect it will be a challenge especially on the exhaust side depending on the level of access for the feeler gauges.

However, given the tolerance range (0.325-0.375 mm) of 0.05 mm for the exhaust clearances, in particular, it looks as though I will need to measure them to a precision of 0.025 mm (the same as the available shim size spacing). Given that most feeler gauge sets have a spacing of 0.05 mm, it is not immediately obvious to me how I'm going to carry out the measurements to the required precision :084:
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Offline Paulhere

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Re: Measuring Valve Clearance (Tips)
« Reply #4 on: March 11, 2020, 09:10:46 AM »
*Originally Posted by awjdthumper [+]
However, given the tolerance range (0.325-0.375 mm) of 0.05 mm for the exhaust clearances, in particular, it looks as though I will need to measure them to a precision of 0.025 mm (the same as the available shim size spacing). Given that most feeler gauge sets have a spacing of 0.05 mm, it is not immediately obvious to me how I'm going to carry out the measurements to the required precision :084:

I have a cheap Draper set 6" long that separate and are in .002mm/.003mm also 0.001" increments. eg marked in both mm 0.30, 0.33, 0.35, 0.38, 0.40mm. and imperial .012", .013", .014", .015", .016" if you prefer old school like me, much easier for my old head to think in thou's.
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Offline Stevie.P

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Re: Measuring Valve Clearance (Tips)
« Reply #5 on: March 11, 2020, 09:18:33 AM »
Also don't get focused on having to achieve the exact figure, i.e mid way, you can allow a little bit either way because the reality is even if 2 experienced techs did them one mans loose is another mans right or tight ... a judgement of 'feel'. The only exact way would be a set of go/no-go gauges.
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Offline cat10

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Re: Measuring Valve Clearance (Tips)
« Reply #6 on: March 11, 2020, 09:21:35 AM »
*Originally Posted by awjdthumper [+]
Fortunately, I will not need to check my 12k valve clearances till the end of the year but I expect it will be a challenge especially on the exhaust side depending on the level of access for the feeler gauges.

However, given the tolerance range (0.325-0.375 mm) of 0.05 mm for the exhaust clearances, in particular, it looks as though I will need to measure them to a precision of 0.025 mm (the same as the available shim size spacing). Given that most feeler gauge sets have a spacing of 0.05 mm, it is not immediately obvious to me how I'm going to carry out the measurements to the required precision :084:

That is a very good point, the 0.05mm tolerance is going to be really hard to measure accurately.

Offline Paulhere

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Re: Measuring Valve Clearance (Tips)
« Reply #7 on: March 11, 2020, 09:34:51 AM »
*Originally Posted by cat10 [+]
That is a very good point, the 0.05mm tolerance is going to be really hard to measure accurately.

There never used to be a tolerance on our old bikes, eg 0.008" inlet & 0.010" exhaust.

This 0.05mm (2 thou) tolerance shouldn't present a problem if it does just do like Stevie says: use 0.35mm gauge as go & 0.38mm as no go.
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Offline awjdthumper

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Re: Measuring Valve Clearance (Tips)
« Reply #8 on: March 11, 2020, 10:13:24 AM »
*Originally Posted by Paulhere [+]
There never used to be a tolerance on our old bikes, eg 0.008" inlet & 0.010" exhaust.

This 0.05mm (2 thou) tolerance shouldn't present a problem if it does just do like Stevie says: use 0.35mm gauge as go & 0.38mm as no go.
I'm not convinced this would be sufficient since a clearance of 0.34 mm (for example) would fail the test but would still be in spec. As a minimum you need to use feeler gauges of 0.325 mm and 0.375 mm for checking the exhaust clearances using them as go/no-go gauges. If a particular valve fails the test then you would obviously need other feeler gauge sizes to determine the actual clearance to enable you to change the shim size to bring the clearance back into spec. Again, the problem I would have is where to find these feeler gauge sizes?
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Offline CB250G5

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Re: Measuring Valve Clearance (Tips)
« Reply #9 on: March 11, 2020, 10:52:50 AM »
I managed to do mine with a set of imperial feeler gauges the queen bought me back in 1981 , when I worked for what was then Post Office telecoms.  they go up in thou's.

It wasn't easy getting them in straight.

In hindsight (always 20:20) at 24,000 I may use my DTI on the buckets and see if I can measure the up/down movement that way.  I'm not sure if the buckets are magnetic, it would be easy to move them with a magnet on a stick, if they are.  I seem to think that's how I got them out this time.
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