I recently purchased a tachometer off of eBay manufactured by Federal Marine & Motor Company. They were located in Chicago , and from the very little I could find on the interweebs, they sold marine engine conversion kits for Ford engines in the late 40’s and early 50’s. The tach looks essentially new, and I wish to use it for my speedster build, but I’m looking for any tech info before trying to figure out if it will work or be suitable for my Ford flathead V8. I know this is a total shot in the dark, but I thought I would try.
I can't help you on the tach, but I have an ancient 4-cyl Ford marine conversion kit in the barn. I'll have to see if it's a Federal brand next time I'm up there.
Got a picture of the back side of that tachometer? "late 40’s and early 50’s" sort of implies a 6 Volt electrical system and before transistorized electronics... If it is a 2 terminal device, it probably has no internal circuitry. A 3 terminal device "might" indicate that it connects to "+", "-" and "distributor" like a modern tachometer. Your luck may vary... Neat looking gauge, if it is a 2 terminal device, it probably is a volt meter with a scale of 0 to 4,000 RPM. Might be possible to build a conversion circuit - If you get lucky, repurpose the circuit board out of a modern tachometer and hide the circuit board out of sight. Russ
Here’s a pic of the back. Being a mech eng, I pretty much hate all things electrical. Been reading up a bit though lately on tachs. I don’t want to screw this thing up. Lol!
Cool looking vintage tach. I especially like the cut-out at the bottom of the face plate. It lets you see at least a little of the "bones" that make it work.
Electrical guy here - I go back to vacuum tubes. I am 99% certain that there is no electronic circuitry inside this meter, the tachometer "magic" was provided by an external box. What I see in the picture: The 2 studs, with insulating sleeves, are the "+" and "-" terminals of a voltmeter (with a 0 to 4,000 RPM scale). The 2 light colored screws attach the meter mechanism to the back cup. The dark colored screw (not quite so sure about this) is the meter zero adjust - don't mess with it, the meter is perfectly zeroed right now. First step: Get a multi-meter and measure the resistance across the studs - no sense of going down the rabbit hole if the meter is open circuit. Start at the highest resistance scale and work your way down. At some point, you should be able to see the needle deflect when the multi-meter is connected to the studs. Expensive route: Have an electrical engineer design a circuit board for it. More expensive route: Track down and purchase an original "magic" box - and then pay big money to have the dried out capacitors replaced... My sort of hack: Buy an inexpensive tachometer (with at least switching for 4, 6 and 8 cylinders) and get it sorted out on your running flathead V-8. Then remove the circuit board and wire it up to this gauge. Play with the 4 / 6 / 8 cylinder switch to get the closest reading (on the high side). Then insert a potentiometer in series with the meter and adjust it to the correct reading. Install everything in a neat box and hide the box out of sight. Russ
There is an upside and a down side to the external box. The upside is that any tach will work on any mill by using the correct box the down side is finding the box and the proper batteries for it. LOL @TrailerTrashToo Your idea about changing the guts is a simple and inexpensive route. I have a green line and a side winder later SW that I intend to mate eventually. In a 180 degree tach it is a little harder because you need to find one with the same sweep to function properly.
Thanks Russ. A few more pics. I think the centre “brass” studs are just for securing the mounting bracket. They seem to be “grounded” to the bracket based on the insulated brass “washers” mounted in the bracket, but what do I know. Looking inside, I don’t see any wires connected to these studs, but I can’t see that clearly. I would need to take it apart to verify that. Nuts removed from centre studs with bracket in place. Bracket removed. Centre studs exposed.
Also, looking inside through the hole in the housing, it seems the “guts” are housed inside another cylindrical housing.
Couldn’t wait and took it apart like a good mech eng. I was wrong (of course!) and it does have wires connected to the studs. Seems the needle “spins” on what looks like the rotor of an electric motor, but I’m guessing this how many function.
Got a bit of a contradiction going on... You can not "ground" through insulated brass "washers". A closer look at the studs will show that they are insulated as they pass thru the rear case. My best guess is that the "+" and "-" studs are passing through an insulated hole in in the metal hold-down clamp. Lots of in-expensive 50's, 60's and 70's aftermarket gauges were built that way. I have installed several over the years. The cheaper ones used a rubber grommet. My 1959 Ford F250 (worn out truck that I had to buy and daily drive after a divorce) came with aftermarket under-dash gauges. Got a spectacular shower of sparks when the rubber grommet crumbled from old age. You need to use a multi-meter and verify all assumptions with a resistance check (ohmmeter setting). Much less destructive than disassembly. You can measure what is connected to what and get an idea of the internal wiring. Russ EDIT: I see your new picture. It is a very traditional meter (gauge) movement. Carefully reassemble it, it looks mint inside. I'm going out to the shop to finish reinstalling a Bosch mechanical fuel injection pump on a Cummins diesel (totally out of my comfort zone)... I'll check back later. Russ
I think you'll find that the brass "tubes" in the bracket are swaged on with insulating washers to electrically isolate the bracket from the studs. The good old (and expensive) way to do what they do with plastic, nylon or fiberglass washers today. Cool old tach. I can't help but wonder if one of the old SW or Sun tach signal boxes wouldn't work. Not that they are cheap and plentiful.
Pulled out my dirt cheap barely functioning multi-meter and got the following info: 20K ohm setting - 1.17 ohms 2K ohm setting - 0.066 ohms 200 ohm setting - needle sometimes moved to about same position above, but then moved back down to “0”. Meter reading went up to about 150 ohms, but then back down to “0”.
Strange reading - Either there is a capacitor buried inside that gauge or your multi-meter battery is almost dead. Do this test on the 200 ohm setting. Hold the meter leads together (short circuit). If the needle slowly drifts, the battery is worn out. Replace the battery, the corrosion of a dead battery will ruin the inside of your meter. Russ
Thanks again Russ. Haven’t had time to check my multi-meter, but will tonight as I’m on the road. Will this “majic” box work? https://www.technoversions.com/TachMatch.html
Looks promising, I BOLDED the key words: The standard TachMatch TM-03 is used in most applications. It allows triggering from a coil ignition, HEI, MSD, and ECU tach output signals. It will directly drive most voltage-driven tachometers, as well as vintage tachometers, such as early Sun, S-W and Radatron units which are typically identified by only having two terminals on the back, labeled + and -. With vintage tachometers, the TachMatch is installed in place of the original sender module, which is no longer necessary. Further down the page: The TachMatch Model TM-03 is designed with computer-controlled internal circuitry housed in a plastic enclosure. A 5-pin terminal strip is used for connection of the wiring (wires not included, but can be purchased below). To help solve any installation problems, it includes diagnostic tools, such as a LED that indicates power and if it is being triggered, and a special test output that can ensure that it is connected properly to your tachometer by providing a 3,000 RPM signal. If you are driving a vintage tachometer, a potentiometer allows you to adjust the output to make your tach read properly. Russ
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