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Sun Tach Dwell Meter


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#1 FixItCharlie OFFLINE  

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Posted June 04, 2016 - 12:06 PM

I was working on one of my tractors that has a Kohler with the points & coil. I happened to think about my old Tach Dwell Meter sitting in the toolbox collecting dust & decided to try it on this. I set it to 4 cylinder & hook it up to the coil & ground. I took the meter reading & multiplied by 4 this seems to be very close to the right idle rpm for this motor. I did a Google search to find any information on doing this & everything I found started talking about dual spark & dividing, multiplying formula to get an accurate reading. My thought on this is What? / Why? These meters were designed for use on the point, rotor, distributer cap ignition used on automobiles years ago. Most of these are set up for 4 sparks per revolution for a 4 cylinder engine, 6 sparks for a 6 cylinder, & 8 sparks for an 8 cylinder. So my thought is if the meter is looking for 4 sparks per revolution & only seeing 1 spark that reading multiplied by 4 should be real close to the correct reading. Am I missing something here? To find a use for a meter that is collecting dust or for many to be trash is a good thing. Reading an analog meter accurately takes some practice but I learned to many years ago to discuss here to read these meters to MIL Specs. With the newer engines this will not work & also the engine needs to be points & coil for this to work. There are newer tachometers that are not that expensive & maybe more accurate but if you have one of these just laying around & are working on the older engines with this type of ignition why not use it. Again am I missing something on this thought. Memory & time often have many conflicts.

 

Charlie   


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#2 KennyP ONLINE  

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Posted June 04, 2016 - 12:15 PM

Sounds logical to me!


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#3 DougT ONLINE  

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Posted June 04, 2016 - 01:04 PM

It takes 2 complete revolutions of the crank for all 4 cylinders to fire. You are only getting 2 fires per revolution unless you are working with a 2 cycle engine. On the other hand, your Kohler is only firing once every 2 revs also. 4 fires on a 4 cyl equals 2 revs and 4 fires on the kohler equals 8 revs. That's why multiplying by 4 is giving you the right reading.


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#4 FixItCharlie OFFLINE  

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Posted June 04, 2016 - 09:07 PM

Yes I forgot about the exhaust stroke. It is nice to take a piece of equipment that was basically retired & find a new use for it.

 

Charlie



#5 HowardsMF155 ONLINE  

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Posted June 04, 2016 - 09:23 PM

So would it be more accurate and less "mathy" to use the "8-cyl" setting?



#6 ol' stonebreaker ONLINE  

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Posted June 04, 2016 - 09:35 PM

  It's nice to use old test eqpt, but I still like my HF phototach.

                                           Mike


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#7 FixItCharlie OFFLINE  

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Posted June 05, 2016 - 12:19 PM

So would it be more accurate and less "mathy" to use the "8-cyl" setting?

It would be the same math except multiply by 8. 8 fires in 2 revs for 8 cylinder. The Kohler 8 fires would be 16 revs.

 

Phototachs are nice to have but I have other tools to use that money for so being able to use this for checking revs allows for the purchase of other tools.

 

Charlie



#8 DougT ONLINE  

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Posted June 05, 2016 - 02:48 PM

One thing you would have to watch out for are engines like the Briggs with the points behind the flywheel. If they run off the crank instead of the cam, it will be firing every revolution instead of every other one.






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