Measuring RPM: A simple solution

[Jim_Inman]

From time-to-time I see posts by folks who are looking for a way to measure RPM of their small engines or others. There is a simple tool that can be easily used on almost any application including automotive, tractors, and small engines. This tool relies on the vibration of the engine as the key to RPM. The device is called a Sirometer and probably the best-known is Treysit. The principle is to place the sirometer onto the engine where you desire a measurement and adjust the inner sliding disc until the reed extending from the left shows maximum vibration. You can read the RPM directly off the scale. Anything with the slightest vibration can be checked, but if there are reduction gears, you have to be a little careful where you make the measurement.

I purchased one of these many years ago from Briggs & Stratton. They still sell them for a bit under $23. Buy one and you'll never have to guess about the RPM of any small engine in a mower, generator, pump or other application.

 

[SeniorCitizen]

From time-to-time I see posts by folks who are looking for a way to measure RPM of their small engines or others. There is a simple tool that can be easily used on almost any application including automotive, tractors, and small engines. This tool relies on the vibration of the engine as the key to RPM. The device is called a Sirometer and probably the best-known is Treysit. The principle is to place the sirometer onto the engine where you desire a measurement and adjust the inner sliding disc until the reed extending from the left shows maximum vibration. You can read the RPM directly off the scale. Anything with the slightest vibration can be checked, but if there are reduction gears, you have to be a little careful where you make the measurement.

I purchased one of these many years ago from Briggs & Stratton. They still sell them for a bit under $23. Buy one and you'll never have to guess about the RPM of any small engine in a mower, generator, pump or other application.

***************************************************************
Thanks Jim.
I've been considering a Honda inverter for the fridge, freezer etc and that looks like a handy tool if there is any way to make adjustments of rpm. Between a Sirometer and a Killowatt meter one should be able to get real close to what the appliances require.

 

[Lawnranger]

I agree, they work great. I've had one for years and use it regularly. I've also read of people taking the magnet out of a non-working microwave oven and using epoxy to adhere the magnet to the back of the Sirometer to help hold it in place. I don't have a magnet on mine as it can limit its uses with all the plastic on today's engines. My Sirometer is branded Tecumseh instead of Briggs but it is a Treysit. Here is a link to one for sale where I got mine: Briggs & Stratton 19200 TACHOMETER UPC Code: 024847905168

 

[Rivets]

Have been using this tach for way too long. Your can also measure hertz with it. This is very handy for those of you who work on generators, where you must set the carbs not to RPM's but hertz.

 

[graydog]

I just found and bought one of those B&S Tachometer (Treysit Sirometer New Old Stock) for $22.50 w/ $0 S&H on eBay. Thanks for the tip. I didn't know there was such a thing.:wink:

 

[WSD]

Elegantly simple device. Do you divide RPM by 2 on 2 stroke engines? Would you double the RPM reading on a 4 stroke twin cylinder like I have on my riding lawn mower?

 

[Rivets]

No arithmetic involved, just read the numbers.

 

[sgkent]

where do all these one posters come from on old threads? Lots of it lately. I feel like we are reading a post equal to comments on the dresses from the 1977 Academy Awards.

 

[bertsmobile1]

When you search a topic all of the old threads come up
And people new to the forum respond to them without noticing the date
I would bet that 99% are browing on a phone