Valve Clearance

bertsmobile1

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Mowers are not the same quality as car engines or even a motorcycle for that matter .
They are the cheapest engine it is possible to make
Because OHV systems tend to increase the valve lash with use you set them on the tight end of the spec so they remain in spec for longer.
The often you adjust them the better
Side valve engines burn the valve seats so the clearance gets smaller over time thus you set them at the loose end of the spec particularly as it is a ardious task on most mower engines .
The only reason to have any valve lash is to account for expansion so when the engine gets hot the valves are not held open .
As for exact measurements don't beat yourself up over it.
I was at a bike show where the CSIRO had a stand as they were on a recruiting drive
The stand had a set of ignition points ( it was a long time ago ) which were connected to a measuring device accurate to within 0.00001"
Any one who set the points to exactly .030" got a prize and you could use their feelers or your own.
By the end of the show not a prize had been awarded and I got a copy of the results which showed no one got to within 0.0005" of exactly 0.030"
They also had a variety of measuring tools there to check the measurement of peoples feeler gauges and again very few .030" gauges were in fact 0.030" from one end to the other
 

wevertx

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Hello I have a Briggs Stratton 18.5 hp ohv so I looked up the Valve Clearance it’s .003/.005 intake and .005/.007 exhaust Not sure about the numbers for example intake is .003/.005 what one am I supposed to use the .003 or the .005 Simple enough to do I’m just not sure about what one to use Thanks for any info you can give me
.003/.005 means it is a go and no go setting. It means that a .003 will go but a .005 will not. In other words .004. The same goes for .005/,007 - meaning .006.
 

bertsmobile1

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In a manual written for engineers it would be 0.004" +/- 0.001"
 

reynoldston

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You are working with .003s one way or the other don't worry about it because you will never get it perfect.
 

nbpt100

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.003/.005 means it is a go and no go setting. It means that a .003 will go but a .005 will not. In other words .004. The same goes for .005/,007 - meaning .006.
It means anything in the .003 to .005 range is acceptable. .0050 is acceptable. Anything greater than .00500001 is not. It does not matter if it is presented with upper and lower limits or with a bilateral tolerance. i.e. .004 +/- .001. Using feeler gauge is a skill. You have to develop a feel. Some may get the .005 gauge to pass. while another will say it does not go. Feeler gauge is a no-go type of measurement. No -go measurement tools tell you a range in which the feature in question falls. It does not give the actual dimension.

With that said, if you are right on the edge of the limit you have to make a judgement call to adjust it or not. I think folks covered this well earlier.

Maybe that is why they call it feeler gauge.?
 

bertsmobile1

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Actually it means anything over 0.0055" is not acceptable
+ or - 1/2 the final digit
As the final digit is a thou then that will be + or - 1/2 a thou
It is a bit problem when Americanizing a UK drawing
The drawing will show 3 1/4" which is 3.1/4" +/- 1/16"
Americans transpose that to 3.125 " which implies that the size has to be accurate +/- 1/2 thou
 
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