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SAE/Metric conversion tables?

Posted by rustyj14 W/PA (My Page) on
Sat, Jan 3, 09 at 11:17

A friend asked me what the Metric setting should be for his chain saw engine spark plug.
I told him i just eyeball them and either that or use a US feeler guage, as i don't think there is much difference in the width of the gap, being it is so small.
But, to ease his mind, i told him i would see if somebody here would or could send the chart showing the conversion settings, to metric, from our good old tried and true method!
He also asked me how to set the gap between coil and flywheel on larger lawn tractor engines. I showed him the strip of birthday card i use. I think he thinks i'm nutty, but it works for me! He also asked if i have a tool to reset spark plug gaps. I told him no, i just tap the side electrode on something hard to close the gap, and a small screw-driver to open it up. (I also showed him the coin-like tool for setting gaps.)
Any help will be appreciated!
Thanks: Rusty Jones


Follow-Up Postings:

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RE: SAE/Metric conversion tables?

  • Posted by ericwi Dane County WI (My Page) on
    Sat, Jan 3, 09 at 12:33

One inch equals 25.4mm. The math is easy with a handheld calculator. If you start with inches, say 0.020", multiply by 25.4 to get the metric equivalent in millimeters, 0.020"=0.508mm. If you are starting with a metric value, say 1.35mm, divide by 25.4 to obtain equivalent inches, using a calculator. 1.35mm = 0.053"


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RE: SAE/Metric conversion tables?

Click the link to see an online conversion site that has been helpful for me.

Here is a link that might be useful: Convertible


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RE: SAE/Metric conversion tables?

1MM = .03937"
Call it .040"
So a plug gap of .75MM would be .030" etc.


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RE: SAE/Metric conversion tables?

Well, Thanks, fellers! Very helpful! But----clear as mud to me!
I guess my use of U.S. measurements over the years has removed any chance of changing to metric now!
But, i'll keep the link you sent, and convey it to my friend, who is as much "in the dark" about metric measuring. And, i'll continue on using my US tools to reset spark plug gaps, and points! And, the cardboard strip for coil gaps!


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RE: SAE/Metric conversion tables?

  • Posted by ericwi Dane County WI (My Page) on
    Mon, Jan 5, 09 at 12:02

Pocket calculators are cheap, reliable, and powerful. But like any tool, you have to use it a while before it becomes comfortable second nature. I use mine to calculate miles per gallon on trips, and a few other routine chores. It seems easy to me, because I can't remember what it was like to learn how to use the thing, back in the 1960's. But I can remember learning how to use a computer, back around 1988, and that wasn't easy at all!


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RE: SAE/Metric conversion tables?

rusty if buy new feller guage it have mm on guage I think it was 25 years ago they start putting mm on guage blades.


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RE: SAE/Metric conversion tables?

Bit Rusty is an old feeler!


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RE: SAE/Metric conversion tables?

Sounds like the pot callin' the kettle "black"!
Bill, i did auto body work most of my working years, about 60 years or so, and we didn't get into the metrics, until we had to buy new sockets and hand tools to work on the newer vehicles. I didn't do engine repairs, or any of that kind of mechanical work when i was employed, just the removal of body parts, etc., and when they went to metrics, i had to buy a bunch of metric sets of hand tools, such as sockets and wrenches, etc.
And, thats why i'm having trouble with metric measurements for spark plug gaps, point gaps, and the like.
At 84 yoa, it is mind boggling! I accessed a web site that somebody here gave me, but its all greek to me. I'm going to let my friend look at it, so he'll understand why i told him to "Eyeball it" and don't worry!
I can download some facts from one site, so if my friend wants it, i'll do it. But, when i tried to understand it---my mind did a flop, so i gave it up!
Too old to change now, i am!


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RE: SAE/Metric conversion tables?

It's really not that hard-
1MM = .040"
.75 MM = 75/100MM = 3/4MM = .030"
OR .040" times .75 = .030"

.8MM = .040" times .8 = .032".

.6MM = .040" times .6 = .024".


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