Tachometers

[arnoldir]

Hey folks, I posted some info on tachometers below as a response to the mowing RPM question. I also asked, and now can answer the Diesel Tach question. The folks at Tiny Tach have a 12 volt vehicle powered version for $65 that uses a sensor clamped to the injection line. Anybody have any experiance with this type ?

[BigSix]

I'd like to find an inexpensive, hand-held tach I can use to set idle and max. engine RPM, on single-cylinder engines. Now that one can purchase a 7-function digital multimeter for only $7.99 (Harbor Freight, but I have yet to see it--just ordered it for a back up to my decent quality analogue multimeter) I'm hoping to find a tach for c-h-e-a-p. I figure it could have an inductive pickup off the plug wire, and then you'd only have to know if your engine fired every time or only once in the four-stroke-cycle, in order to read the correct RPM info for your mill. I have also heard of a type one simply holds against the engine. (I think it's used with model airplane engines, and so may not be accurate enough for our use, as those little fellers spin in the teens to 30,000 RPM, in marine applications, I've read. Zounds!) Has anyone seen anything like either one of these tachs? Peter

[HubbardRA]

BigSix, Go the the question below mowing speed. Woody just posted a link where you can get a vibrating wire tach for about $13. I have used these before, and they work great on one or two cylinder engines. Just lay it against the engine or even the hood, turn the dial till you get the maximum wire vibration, and read the scale. We use the to check the governor speeds on all the stock tractor pullers at our events. They work very well, are easy to use, and are very repetitive. I haven't changed the governor setting on my son's tractor in two years, and they have read the same speed every time it has been checked. By the way, I just ordered one of those tachs from Woody's link. Rod H

[Dutch]

Peter, Last year, my 20yr old analog VOM died. I bought one of those $7.99 digital jobs. SAVE YOUR MONEY! Used it 3 times, then bought a $100 Fluke.

[HubbardRA]

BigSix, They are round. Nothing more than a coil of stiff wire in a round holder with a calibrated dial. Seems the speed at which a wire vibrates is related to its length. With the tack against the tractor, the vibration is caused by the rotation of the engine. You adjust the wire to get the maximum vibration, then you read engine speed off the dial. The engine RPM and wire vibration speed are the same. Have used these units many times as a Tech Official at tractor pulls, but just ordered one for myself today. Now I can check the engine speed before I go to the track. Rod H.

[BigSix]

Rod (and Woody): Thanks for the link, which I found. Just want to make sure the pic is right--is the Vibratach round? I hit the "pic" on the tool site, and something that looks like a clay pigeon came up. If that's the thing, I will buy one, at that price, now that I know they actually work. I (wrongly) assumed they couldn't accurately show low rpms, like a 1,200 RPM idle. Apparently they can? Thanks again, Peter