I picked up this tachometer recently and it is weird. Fits a 3 inch hole and only has a spot for a 1 wire hookup. Anyone know what this is for?
The 8 grand scale makes me wonder if it was from a boat or something similar. That also means it wasn't produced before the 60's. Very few engines had that rpm capabilities. I remember seeing 3" tachs in large trucks but none with that scale. ????
Just found this, it’s either fact or someone’s understanding,,, you may understand it Mark. RVI (Inductance) reads the pulse from the cable that runs from the coil CB terminal to the distributor. Follow the single wire that connects to the distributor and it should run to the coil. You need to splice a new long wire in there so that instead of running directly between the 2 components it runs via the loop drawn in the picture above that Mike posted. Basically, just re-route the wiggly amps through that loop so that the revcounter can 'view' the magnetic field that the coil pumps down to the distributor. It's a bit like using a stethoscope to listen to the beat of someones pulse. RVC revcounters us a separate single wire direct from the distributor and it doesn't return. A bit like the oil pressure capilliary gauge, it just looks down a wire to see what is happening at the other end. Hope this makes sense.
This is one of those things that differs just enuff to make thorough thinkers say "WTF?" when the reality is that it's right there. Usually 3 or 4 wires that are ground, signal, and 1 or 2 for the light. Light is a socket so take 2 away. Body has its own ground for the works inside. Give it a signal from the ign and you're off to the races. My take anyways. The 8K is intriguing given the obvious age. Quite possible it's a powersport tach, bike or boat. Not sure how high a full size outboard spins.
Barrelnose pickup probably is on to something. (utilizing inductive pickup to operate the tachometer) I found a schematic for the tachometer wiring on an older Datsun. Could the Sun tachometer shown have two connection points? With one being the center threaded lug, and the gear toothed area being the second connection point, thus a bolt on two wire connector was used. The tachometer has to be wired in (or wires shorted together) for the vehicle to operate.
Ok, I originally hooked it to my distributor machine and it didn't do anything and it made the machines strobe go out when connected. So, before I ruined my machine I hooked a battery and ign coil to it. and when the case was grounded to the dist it started working. It read 3000 rpms when the tach on the machine was reading less than 400 rpms. So it appears like it is a single cylinder tach. Possibly for a snowmobile?? or maybe a single banger bike? here is a video https://www.youtube.com/shorts/vmtC6aB-SDI
Doesn’t look like an inductive pick up to me. Do you think it should work with a control box, some of them have one feed from the box and an earth, the control box allows for use with multiple cylinder numbers?
A little Dr Watson for ya Sherlock. We know that there's wires to cut for different cylinders in some tachs. If it was built for a 1, 2 or even a 3cyl 2 stroke get up every pulse is a spark. All 3 plugs fire at the same time in a triple, both my Harley FXE plugs fire at the same time (fkn old shovel, no jokes, I love em). Now perhaps your machine has gone CSI and found "evidence"...?
Never seen a Stewart Warner with the SW covering hundreds under RPM. Might be a fugazi for some prop or display.
That was me tilting it to keep the glare off the picture , it does seem like the gl*** is turned though
I would vote 2 stroke like a snowmobile with 8000 rpm I don’t think an industrial engine would need to so that high. Late 60s and early 70s lots of small snowmobile manufacturers that might not be big enough to put the brand on gauges or aftermarket kit for snowmobiles.
I'd bet there's a model number inside that gl*** somewhere. Like on the face "below grade" so to speak, but I'd also bet you looked into numbers etc already to no avail.
My Dads 6.2 Diesel had a tach (only to maybe 4k though) but it just had a single wire hook up. There was some type of sensor on the crank pully that went to the tach.