OK Here is a tough one!

In Michigan, the DNR uses a sound meter and tachometer to check sound levels. Whats unique (to me) is that the tach is a resonance tach. They dial in a RPM by extending or retracting a spring to a calibrated length as I remember it. They set the unit against your transmission or engine a have you gas it til the spring tip vibrates wildly, thats the rpm level they dialed in, then they do the sound check. Does anyone know where to get one, I have searched the net with out any luck. The thing thats nice is you don't have to hunt for the plug wire to get readings for an electronic tach. Help!

Hey Jim,

Ive heard the same thing about our goofy testing procedure. I wonder how acurate those tac thingy's are. Going off engine vibration?? that dont seem too reliable to me for some reason. What if you have some old non counterballanced bike that vibrates like an old harley. Would that affect the reading?

I have no idea were they get them. Ive never seen one in use. Ive never been sound tested. I dont know how Ive escaped that one so far. Luck?

This will be the SOP for all federal and state forrestry service that will do the testing. I just placed a SenDec RPM / Hr meter on my 426 just to make sure they are in limit.

I have heard that the state method can be off as much a 1000 rpm

I will be checking the accuracy of the RPM meter this weekend

in the mean time check this out


This model is 806-100-1032 39 bucks

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E G O Thanks for the info. You always provide us with good/reliable information. Jim

Hi Jim,

The meter you've heard about is from Briggs and Stratton, the Trysit Sirometer Vibra-Tach, 800 to 25,000 rpm, part #19200. EGO, I'll have to disagree with your +/-1000 rpm possible errors info. Realistically, you could expect a few hundred rpm error in a bad application on a bike. The accuracy is pretty good around 3000 to 5000 rpm where most engines are tested. The physics of the device are: a piece of spring wire with a small loop formed on it's end to more clearly define it's resonant frequency vs extended length behaviour; counterbalancers and all, the fundamental frequency of your crankshaft is still dominant in a single cylinder engine; the spring wire is nearly totally undamped (except for air resistance) and as such really responds dramatically when mechanically excited at it's fundamental frequency. Great little piece of engineering in terms of performance vs cost. Durable, no batteries too.

This is one of the meters referred to by MIC's booklet.

If you're getting into sound testing, get yourself a booklet which contains the essence of SAEJ1287 and the rpm charts.

I staed I have heard I did not say it was accurate.

But thanks for diagreeng with me.

But even 300 - 500 rpm can rais etheDB level dramaticly

I set the idle to run 4500 and test do not use the throttle.

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