Tachometer ?

[Kaiser2boy]

I dont see how this could work and be accurate.
Couple things to consider, just on the engine I swapped into my Jeep, an LA/Magnum 5.2 conglomeration. There are 2 ring gear tooth counts available, depending on where the starter is located in the bell housing.
I would think for that to work you would need to have a tooth missing so that it could recognize the longer pulse, and therefore know when 1 revolution had been performed. Could probably work with half of a tooth removed, but I dont think I want to try to start my rig with either a half, or whole, tooth missing from the ring gear.

Just a thought, If only one tooth was missing it would only be a very tiny error. Plus it sounds like it does not matter as long as you dont continue to lose teeth. Once it is set to what ever teeth you have it should be ok. So brush your teeth regular and remember to floss and it should be OK.

[Frank Irons]

If, as you seem to imply, there is no trigger device attached to the flywheel, then the circuitry must be able to recognize a repeating pattern. That is the only answer I can come up with.

The speedometer in my M37 works on the same principal. The trans has a 40 tooth gear that the pickup senses and transmits pulses to the speedo. Gear ratio and tire size has to be considered though. In my application it generates 127,000 pulses per mile.

Frank

[Charles Talbert]

The speedometer in my M37 works on the same principal. The trans has a 40 tooth gear that the pickup senses and transmits pulses to the speedo. Gear ratio and tire size has to be considered though. In my application it generates 127,000 pulses per mile.

Frank

Frank, what you have on your speedo sounds like the hall effect generators we use with electric speedos. That is something totally different from a self energizing instrument like the tach being discussed in this thread. The pulse generators require an electrical power source, and are much more involved to calibrate. The one we use can be calibrated to read right on also, they can be set up to correspond with any gear ratio and tire size, no problem. All this must be considered when figuring pulses per mile in order to come up with a correct set of figures for use during set up. I have grown to like these as well; mainly because various styles of instrument types are broad. The older mechanically driven stuff is fading from the scene fast.

[Frank Irons]

I think that I should have said picks up 127000 pulses instead of generates. It is a simple little pickup that senses the spaces in the 40 tooth gear.

Frank