What RPM tachometer should I buy - Snowblower Forum : Snow Blower Forums
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post #1 of 24 Old 01-05-2016, 10:56 PM Thread Starter
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What RPM tachometer should I buy

I am thinking of getting a tachometer so that I can test engine RPMs.

I don't mean a permanently fixed unit for measuring hours or for constantly monitoring RPM.... I just mean a test unit for diagnosing how an engine is operating from time to time.

Can you offer any low-cost but reliable suggestions? Preferably with a link.

I believe there are some where you hook a wire close to the spark cable and others that are non-contact laser point-and-click.

I am looking for reliability, longevity and accuracy over convenience or gimmickry. I don't mind wrapping a wire if that's what it takes to get the job done and if those models are simpler and therefore more reliable (I'm guessing they might be).

Any thoughts?
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post #2 of 24 Old 01-05-2016, 11:04 PM
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If you have a smart phone they have apps for that.

Download and view Acoustic Tachometer (RPM) for Android | AppDownloader

Harbor freight: LCD Automotive Multimeter with Tachometer Kit

Digital Photo Sensor Tachometer


inductive timing light | eBay

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post #3 of 24 Old 01-05-2016, 11:06 PM
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I just use a Tiny Tach and wrap it around the spark plug wire as you describe and clip it. It looks like the models have been updated since I got mine. It is tach only, most seem to include hours too now. I forget how long the battery is supposed to last, I better test it!
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post #4 of 24 Old 01-05-2016, 11:17 PM Thread Starter
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Thanks so much! Wow a smart app.... interesting.... probably does some kind of fourier analysis of the sound and reports peak frequency.

Hmmm. I guess you get what you pay for (sometimes). Do you have any opinion on this much cheaper thing I found on eBay? I don't really need the multimeter capabilities (although that's nice) I already have a multimeter.



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post #5 of 24 Old 01-05-2016, 11:48 PM
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That should work if you have something to point it at. A small piece of reflective tape is installed and it times the reflections. With the belt cover off and a piece of tape on the edge of the pulley say.
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post #6 of 24 Old 01-06-2016, 12:03 AM Thread Starter
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Quote:
Originally Posted by dbert View Post
That should work if you have something to point it at. A small piece of reflective tape is installed and it times the reflections. With the belt cover off and a piece of tape on the edge of the pulley say.
Oh I see... that's not very convenient then is it? Mirrors on pulleys and taking off the belt cover.... I assumed you could just point it at the engine and it would detect micro-vibrations and report that as a frequency. (I guess that could work).

So in that case, I am thinking that the wired version seems much easier.
I assume you just hook that clamp thing around the spark cable and it uses electromagnetic induction to figure out the number of sparks per minute.

If that's true I think I'll go with the wired clamp thing.

I'm sure the user manual will explain all this but.... you probably have to multiply the number of sparks per minute by 2 to get RPM ... right?
If that's true.. hopefully those meters have a selector where you tell it if you have a 2-stroke or 4-stroke engine. They must do.
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post #7 of 24 Old 01-06-2016, 12:28 AM Thread Starter
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Just found the manual... it says it's for multi-cylinder engines (3 and up)
That means having to do some arithmetic to get the correct value for a single cylinder 4-stroke snowblower engine.
Also, it's probably different arithmetic for a 2-stroke single cylinder. (Additional factor of 2).

http://manuals.harborfreight.com/man...5999/95670.pdf

In fact, I just found a thread discussing these issues..
http://www.diygokarts.com/vb/showthread.php?t=10545

So it sounds like Tiny Tach is the only one that "just works" out of the box without mental arithmetic.
So I think that's my answer!

Tiny Tach TT2A $41.99 here:
http://www.ebay.com/itm/Tiny-Tach-Ho...AAAOSwgQ9VlV~M

Tiny Tach TT2A Manual:
http://www.papteam.com/PDFs/TT2A.pdf

Last edited by unknown1; 01-06-2016 at 12:55 AM. Reason: cleaned up rambling
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post #8 of 24 Old 01-06-2016, 05:48 AM
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Hardline makes a similar tach. Wrap the plug wire & fire away.
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post #9 of 24 Old 01-06-2016, 07:02 AM
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Quote:
Originally Posted by stuart80112 View Post
Just found the manual... it says it's for multi-cylinder engines (3 and up)
That means having to do some arithmetic to get the correct value for a single cylinder 4-stroke snowblower engine.
Also, it's probably different arithmetic for a 2-stroke single cylinder. (Additional factor of 2).

http://manuals.harborfreight.com/man...5999/95670.pdf
Yeah, the design of that meter is rather silly.

It's apparently designed to measure the pulses from the coil in a coil + distributor setup as found on (older) automotive and similar engines. For a fixed tach like the one in the dashboard that makes sense as it's driven off the coil primary. But for a portable tach that clamps onto a high-tension wire, it would have been much easier to skip the "number of cylinders" selection and associated circuitry, and just have you clamp it onto a wire going to one cylinder. Then the only variation is between 4-stroke which fires once per every two revolutions and 2-stroke which fires once per revolution.

With OPE (outdoor power equipment) engines it's even easier, as both 4-strokes and 2-strokes fire every revolution. So a tach that's designed for such an application and reads the signal from the spark plug wire should never require any math.

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post #10 of 24 Old 01-06-2016, 07:23 AM
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Instead of spending 42 bucks on a "Tiny Tach" why not just buy the generic tach/hour-meters that you install the same way for $10 on Ebay ??
And when I say install I'm talking about wrapping it's lead around the spark plug wire but not bolting it to the machine so you can use it on different machines as a portable tach.



It's not as handy as an inductive pickup meter but it functions the same as the Tiny Tach for 30 bucks less.

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