Hand held tachometer

[Dan in Ohio]

What do you use to gauge engine RPM's on your tractors that do not have working tachs. Maybe it would just be easier to try to get the tach working.

 

[F-I-T]

Use the pto.

 

[Bob Harvey]

I have a Stewart Warner hand held that you put up against the center of the crank or any center that spins. HTH

 

[Dave in SV]

Is there a ratio/formula needed to calculate engine RPM from PTO RPM?

 

[55 50 Ron]

Well - - PTOs are standardized at either 540 or 1000 RPM so set your engine speed to provide that.

Oh yah, THE "formula" is set in the design by the tractor manufacturer so why would you need to know it? It doesn"t do you any good even if you knew it!! You can"t change it!!

 

[Kurt_JDB]

Here is a hand tach that I picked up on ebay for 15 or 20 bucks. Put it right on the end of the crank.

 

[Dave in SV]

Then why would FIT suggest measuring PTO RPM when they want to know engine RPM?

 

[F-I-T]

The engine specifications will give the rated speed of the engine, and the subsequent standard PTO speed, could be 535 on some, 540 on most.

 

[Bob Harvey]

Well, that is a little fancier looking than the one I've got, but mine came with a variety of rubber tips for different applications. Wish I could say mine cost $20 or less !!

 

[Dan in Ohio]

Kurt,

I like the looks of that. I have an old AC hand held tach that has a small viewer to see the speed but it is not very clear. I only have one pointed tip for it, yours looks like a flat tip.

 

[jCarroll]

Because FIT is more experienced than most who read these posts.

Not all tractors have access to put a tach on the crankshaft. PTO is an easy place to get a measurement of engine speed.

 

[Indiana Ken]

(quoted from post at 15:59:39 03/09/12) Is there a ratio/formula needed to calculate engine RPM from PTO RPM?

You will need to find the engine RPM for a PTO speed of 540 RPM. This should be listed in the operators manual.

For example: on my 4000 Ford an engine speed of 1750 RPM results in a PTO speed of 540 RPM. Therefore, the ratio is 1750/540 and to find the engine RPM from the PTO simply multiply the measured PTO RPM by 1750/540.

 

[55 50 Ron]

Because the two are directly tied together and you can't change that by 'knowing some formula'. It boils down to the fact that if you set the proper PTO RPM the engine will automatically be at the right RPM assuming all mechanical parts are correct.

 

[Kurt_JDB]

This was made by a company called Biddle. Came with a number different tips and extensions. I bet it was a high dollar unit when new. Works CW or CCW.If you search for hand tachometer on ebay. There are lots.



Kurt

 

[Dave in SV]

Ron, I know that the PTO/Engine RPM relationship is non-changeable. The original poster did not ask how to set "the right" engine RPM, or whatever you are leading up to. He asked how to (measure) engine RPM, and FIT suggested measuring at the PTO. I guess Dan in Ohio could rev up the engine til the PTO measures 540 (or 1000, which ever the case might be), then, per the design specs, he would know what the engine RPM is... but that will only work at that one particular RPM. I was simply asking if there is a way to determine any engine RPM by measuring PTO RPM and calculating accordingly.

 

[Dave in SV]

Wouldn't it be possible to make an electronic tach that would count the spark to a sparkplug, clock it against an internal standard, and come up with a calculated result? My dad used to have a pencil-looking device that he would hold up to (or maybe touch) a plug wire, and a yellow/red glow would flicker in a sight window on the side of the "pencil", indicating whether there was a live spark or not. Surely with todays electronic technology, a pencil-tach could be made... heck, something probably already exists, yes? (Pssssst, 55 50 Ron... don't slam on me, OK? I'm just trying to explore and learn.)

 

[F-I-T]

So, once you look in the book and get the engine rated speed that makes the 540 pto speed, you have the ratio. If the rated speed is 1080 for example, then the engine speed is always twice the indicated pto speed. Tough to explain that when typing on a cell phone.

 

[H+60]

I have an old dwell tach that I use. One wire hooks up to the coil wire, other to ground. They are not used much any more, ebay should have one cheap.

 

[Dave in SV]

Yep, makes sense. As always, thanks Frank.

 

[Dan in Ohio]

Got out my old AC hand held tach that I unknowingly picked up at auction years ago. FIT I used it on the PTO as you suggested, worked real well.

<a href="http://s614.photobucket.com/albums/tt221/DaninOhio/?action=view&amp;current=March102012013.jpg" target="_blank">

</a>,

<a href="http://s614.photobucket.com/albums/tt221/DaninOhio/?action=view&amp;current=March102012001.jpg" target="_blank">

</a>,

That is a little fast so I slowed her down (high seat 60 std).

<a href="http://s614.photobucket.com/albums/tt221/DaninOhio/?action=view&amp;current=March102012006.jpg" target="_blank">

</a>

That looks good about 540. That dial is really not that hard to read, bright sun made is seem bad.

Thanks for the help all of you.

 

[rustyfarmall]

Actually, I think 600 RPMs on the pto shaft with NO load would be about right.

I used that same method on my 1940 Farmall M, and the M seemed a little slow in road gear with the governor adjusted to give a no load speed of 540 rpms, so I bumped it up to about 600, and now the road speed seems just about right.

 

[Dan in Ohio]

It does seem like I slowed it down a lot. I have another 60 that I will check it against on Monday.

 

[LarrySTN]

I use a non-contact digital tach the reads a reflective stip or a polished mark on crank pulley or flywheel. The digital non-contact tach is affordable on fleabay or your favorite online auction site.