any instrument repair guys here?

[flyguy]

My recording hourmeter on my tach gave up the ghost and I thought I would take a look as I have had some experience with similar stuff having worked in a calibration lab. Actually plan to buy a new one but thought I would see if I can get it to work again anyway.

Question: The only thing I see that looks like a challenge is getting the pointer off without wrecking something. (and getting it back on--)
Anyone know the secret trick for doing that?
Darryl

[Hank Jarrett]

Re: any instrument repair guys here?

"Officially" you do understand you are NOT allowed to repair instruments yourself. Of course you are only taking this one apart for educational purposes, right?
If you want to actually use the tach in your plane again you should consider sending it to a certified instrument shop. I have had a bunch of instruments apart and they are FULL of very delicate parts (they are only good for decorations now, and were worth NOTHING when I started).
As far as removal and replacement of the hands the easiest way to learn is to talk to a watch or clock repair person (a horologist). There are many types of mounts for indicators and he will be able to advise you when he sees it (as long as you convince him you won't ever use it in a plane again).
Hank

[Larry Lyons]

Re: any instrument repair guys here?

Hank you are right, I have several old clocks that I have brought back from the dead. Some I could take care of myself, some I killed! LOL There are several ways to take them apart but only one way to put them back together. Actually there are special tools for that job but not cheap to buy; and even more expensive to learn how too operate.
Again do not ask me how I know, Larry

[flyguy]

Re: any instrument repair guys here?

Why Hank,
What would make you think that I would even consider doing such a thing.

I mean a guy who has only worked on unrelated things like a couple years doing complete rebuild of analog meters including the precision movements; written a repair/QA manual for calibrating altimeters and encoders and set up the test equipment for the shop; worked as field service rep on laboratory equipment for such outfits as Stanford Research Insititute; calibrated standards for the Apollo program; and with only 45 years of experience calibrating and repairing just about every type of temperature, pressure, electrical, digital, fiber optical gizmo imaginable; certainly a guy with such limited experience would never consider repairing a device that is fairly insignificant to the safe operation of a somewhat tired 60-year-old airplane that can't even carry a passenger.

Wouldn't even consider it for a moment.
Darryl

[Hank Jarrett]

Re: any instrument repair guys here?

We think alike. The fact that we "can" fix it doesn't mean it's legal. I wouldn't even CONSIDER repairing a part that was well within my capabilities if I knew I didn't have the correct piece of paper from the appropriate regulatory agency. I would ALWAYS take it to the repair shop and pray the guy who actually knew what he was doing got my part.
Seriously, everything I have heard about Keystone instruments has been good except their speed. Their turn around time seems slow, but the quality of work seems first rate. Good trade from my point of view.
Hank

[flyguy]

Re: any instrument repair guys here?

Didn't even cross my mind to have it repaired. Just naturally figured it would cost about the same as buying a new one, particularly since it must be labor-intensive. I could be wrong about that, no experience. Just figured to buy a new one.
As I have said this plane has been a wonderful flier and has cost me almost nothing in parts, so I figure maybe I should cut the ole' girl some slack and stick in a few new goodies. I have added a few new things and replaced some, but it has been pretty economical. I have put in a more than a bit of labor and TLC, but it has been a labor of love for sure.
The new struts should clear my conscience some .
DC

[flyguy]

Re: any instrument repair guys here?

The answer to the question posed is:
If someone were to place a small screwdriver under the flange of the brass ferrule attached to the pointer and at the same time touch a soldering iron tip to the center of the pointer where it would heat the ferrule, applying a little prying pressure between the meter face and the ferrule, I am absolutely sure that the pointer would pop off easily without any damage to other components. It would be obvious that the brass ferrule with the pointer attached was a press fit, possibly with differential heating used to help installation.
If he were to remove retaining clips, screws, ect. and carefully disassemble the unit taking out the magnetically driven can, I am 99.999% sure that he would be able to see that the first input worm gear for the hour meter would be pretty much chewed to pieces.
If, in fact, he could inspect the other gears, probably four of them, he would see that they were pretty well gummed up with dried lubricant, dirt, and other debris, and that it would be very likely that it would jam said gears and cause the failure that he might find, were it possible to do so.
Were he to do all this he would rightfully conclude that replacement of the tachometer with a new unit would be required because the extent of the wear and damage would likely preclude economic repair.
If he were to do all this he would have the reward of knowing exactly how aircraft tachometers/hourmeters function and at least be aware of one failure mode. He could then purchase a new tach clearly with the understanding that it was the best, and indeed the only, way to proceed.
Darryl

[Hank Jarrett]

Re: any instrument repair guys here?

And if he cleans up the face and puts the pointer back on he will have a GREAT desk piece. They look really good mounted on a piece of wallnut with a picture of the plane.
Hank
Maybe set the hours meter to the number of hours you had flown in the Taylorcraft on the day the picture was taken. HMMMMMM! Got to look at my box of junk instruments.

[Larry Lyons]

Re: any instrument repair guys here?

Love this thread, I have several of WW 2 vintage and would love to get them back to some sort of shape. Plus I have an innate interest in stuff mechanical. Larry