tachometers

If you can get hold of an alternator sensed meter, an inductive crank position sensor and mount an reluctor with a suitable number of teeth on your shaft you could use a vehicle one, but I think do not understand why you need RPM to time a shaft (unless you mean measure the speed of a shaft).

You might be able to get an ignition sensed unit to do the same with similar extra bits, but I doubt it will be easy.

There are cable driven units around, but probably any car ones would have been snapped up by the restorers. Try finding someone breaking machinery that may have a revcounter fitted.

Easiest of all try ebay for a mechanical one to hold on the shaft or even a stroboscopic one to shine at a piece of white or silver paper you have stuck on the shaft.

If you want to measure rpm - depends on the engine, how accurate or responsive and how much money you want to spend.

if you look on ebay for kart racing rev counters there are usually a few to be had. These pick up the spark from a wire wrapped around the ht lead and counts the number of pulses. Most can be switced from 4 stroke to 2 stroke and count in units of 10 upto 15 or 20k rpm (some will give you a resolution of down to 1 rpm which would only be much use on a slow running engine). Not much use for a diesel or a long stroke 30 rpm chug a lug.

We used to have a little device that plugged into our digital multimeters that would count flashes of light - piece of aluminium foil stuck on a flywheel, a blob of white engineering crayon or a dollop of tippex usually did the trick. Only thing is I am damned if I can remember what meters we had - most likely Fluke, or how expensive they were - if they were fluke I'd guess they were fairly pricey. Its quite possible that optical tachos are available from other suppliers.

If you want to time a shaft for its position in rotation when being turned by hand etc then a home made timing disc should be plenty accurate enough.

Off the top of my head I can't think of any other definitions for 'time an engine shaft'

Hope this helps

Dudley

If all you want is a crude tacho, any cable drive speedo will work. If you can get access to another engine with a tacho fitted, you can calibrate it that way. Failing that, time the odometer. Like others, I question how you time an engine with a tacho though.

You can get a cheap but perfectly servicable optical tacho from a model shop, they use them to measure the speed of a prop. A bit of black tape on a shiny surface or vice versa is all that is needed to make them work with other engines.

Greg

A friend recently bought a new tach for his yacht, a three cylinder Kubota engine. This unit has a sensor that clamps onto one of the injection pipes, really simple! (for a diesel, that is)

I wonder if you could adapt one of those little speedometers they fit to bicycles - a digital readout, not sure if you can get rpm out of them though.

Snip

FWIW

I understand that many years ago an automotive "electronic instrument" company produced just such a thing as a diagnostic tool and all went well until they demonstrated to British Road Services. At that pint it went ballistic and gave all sorts of unlikely readings. It turned out to be caused by the play in a worn engine creating all sorts of other pulses that the sensor was picking up. The Kubota may be oK because I think it uses timing gears, but I would be less happy with one on a worn engine using a timing chain..

What you are looking for is called a "tiny tack". A google search will turn up both the web site and several other references. Apparently they are much used by the home built aircraft crowb.

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