Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

I'm trying to see if my used Toro 824 Power shift is running at the proper high speed.  I borrowed a sirometer but the instructions are kind of vague on how to use it..  With the tach held against the engine and the wire slowly extended, what am I looking for?  The wire to stop vibrating?  It does this at both 3000 and 4000 rpms.
Thanks

I have one of those Sirometer tachs that I use on my diesel. It's way out at my camp 60 miles in the bush and snowed in with over two feet accumulated. Therefore, I won't be going out there any time soon. If properly used, the wire should resonate with the engine rpms. When that happens, the end of the wire with the loop on it should almost look like a solid blur. The more intense and shorter the length of the blur, the more accurate the reading. They are very accurate if properly used. However, for other than diesel engines, I use an electronic mini tach that is run by wrapping a wire from the tack onto the spark plug lead. No complication, no guessing. The reading is digital and very accurate. I recommend you try using a digital device especially if you're trying to adjust the engine rpm.

i think my briggs and stratton wire tach is what your talking about.it's black bakolite and looks like a mini fish tape.i run the wire out very slowly till it vibrates at it's wides spot  and check it . then i'll redo it once or twice to check my accuracy.  if you go past the widest arc it will start to lessen again. i think i'm using it right?

you are correct.  widest arc is what you want.  They are extremely accurate

Knee_Biter wrote:

You mean widest arc when it's in a constant oscillating blur right? I feed out the wire until the end looks like it's making a solid blur. I go slightly past that point then back it in again to get it to maximum intensity. I guess that would be the widest arc of maximum blur. Thank you for correcting that for me. I was working on memory from over a year ago when I set up my diesel at camp.

that's correct borat! the point where it reaches the widest blur or wiggle is the rpm's.i've even used it to see what my cub cadet mower blades were turning at.

Doesn't it also go to a wide arc on multilples of the freq/rpm?   If it is set to 1000, will also show the next harmonic of  vibration at 2000?

It has been a long time since I was paid to use one...

Friiy

Here's 31pockets on youtube using his sirometer. Does this help ?

http://www.youtube.com/user/31pockets#p/u/1/f4zzx3e4lRU

Cheers,
Len

LennyB, nice find. That looks like a great Utube series.

 

The wire length will vibrate the most when it’s vibrating at the same frequency as the engine.  That’s when it’s “blurred” and swinging the most as it has the most energy transfer from the engine to the wire.  When the wire is vibrating the smoothest and most it’s the best match of the engine RPM.

 

Lengths of wire are calibrated to the dial speed RPM readout. 

 

When vibrating the most that’s the resonant frequency and will be what they call vibrating in sympathy with the resonant frequency - the engine’s RPM speed and read out on the dial for that length of wire.    

 

If you set the engine to 1800 RPM and got the wire to vibrate the most then set the engine to 3600 RPM the wire would have two vibrating waves and look like an 8 flattened out but very regular looking and smooth.  The middle is called a node and does not vibrate so if you could put your finger on it your finger would not feel anything.  The two waves at 3600 RPM would be showing the first harmonics of the 1800 vibration.  

 

I’ve read a few times where the vibrating tachs were checked against pricy digital bench meters and read the same. 

For setting an engine you can tape it to a snowblower and set the wire for 3600 then adjust the engine.