Tachometer fix

Bkpigs · Jul 30, 2016

I got the bezel and glass removed from a tach of a Farmall 504 but cannot get it apart any further than the picture. The tach locked up on me and I am trying to free it up but cannot get the input collar removed. I put the tach in a vice and tapped the collar to the left and right using the hole molded into it. It wouldn't move and I didn't want to hit much harder with the fear of twisting something. Can anyone help me on the next step?[/img]

JF in MI · Jul 30, 2016

I had a friend with a similar problem in an old aircraft tach. IIRC the shaft locked to the bushing inside. This was 20 years
ago so I don't remember how we fixed it. I can tell you that the most delicate part is that clock spring so be super careful of
that.

Bob Bancroft · Jul 30, 2016

What part locked up, the input, or needle? Can you turn either one? If you can get both to turn at all, maybe with lubing and working it you won't need to take it apart any farther. I don't think there's any direct connection between the two parts. I think there's probably just a magnetic "drag" cup in there. You don't mention an hour meter. Is that what the gearing is for? Is that stuck too?

Bkpigs · Jul 30, 2016

the needle moves freely. I cannot turn the cable when it is inserted into the tach. The bushing inside is what is stuck, just needing to know how to get to it from here.

gab · Jul 30, 2016

Back in the old speedometer days the bushing would sometimes squeal and the needle would jump wildly. There was a squeeze bulb tool that you filled with some kind of light red oil and squeeze into the head. Wasn't always 100% effective but fixed a lot of them.

Bob Bancroft · Jul 30, 2016

Can you grab the brass input sleeve with pliers, get it turning, and work lube into it?

Steve@Advance · Jul 30, 2016

I would try some penetrating oil, let is soak in for a day or so, try to get some movement out of it with a rag wrapped around the brass part and twist with pliers.

If you can get it to move, keep moving it until it turns freely, maybe put a drill chuck on it, keep running and oiling it to get it turning as effortlessly and smoothly as possible. It is necessary that it turns completely free with no binding.

If it won't break loose, or won't free up, there are companies that restore instruments. They do a fantastic job, but it comes at a price! It would need to have some historic value to justify their service.

JF in MI · Jul 30, 2016

Another thought (not a good one) came to me; There has to be some sort of gear reduction in that housing for the proof meter. I
hope nothing is broken in there but if there was I would think the input might have the slightest back and forth turn to it. If
its the bushing then some minor heat might help.

flying belgian · Jul 30, 2016

No, No, No. Use no heat. Miner or otherwise.

FBH44 · Jul 30, 2016

Don't know anything about it, other than I think instrument repair is a different animal from clutch / brake / carb / steering repair. Seems like it might be a speciality.

MARK ROBKE · Jul 30, 2016

Usually you can tap the end/bottom side of the brass inlet where the cable tip goes in,and it will free up and then you can rotate it,and lube it.Just tap it upwards from the bottom.I used to do it a lot,before electric heads came along.Mark

JF in MI · Jul 31, 2016

Yea, you're probably right.

Bkpigs · Jul 31, 2016

i found a small screw driver to fit into the input for the cable. I then turned it and it freed up. I put plenty of pb blaster on it and worked it for a while. Thanks!

Tachometer fix

Bkpigs

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JF in MI

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Bob Bancroft

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Bkpigs

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gab

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