Tach not working

[rotorman]

The tac cable pulled loose from its fitting at the engine side. I removed the fitting and reinstalled it on the cable. Then I screw the cable back on the engine and now the tac does not work. From the engine side I pulled the cable out of its cover and it is not broken. Next I unscrewed the fitting from indicator side and ran the engine. The cable does not turn. At the engine side the cable is screwed into the engine such that only about two thread show so I believe it is fully in. Is it possible that the cable is not engaging on the engine side? Or what else could be the problem?  

Edited June 11, 2023 by rotorman

[MikeOH]

With the caveat that I have NO experience with aircraft mechanical tachs, only automotive, I would check your 'reinstallation' of the tach fitting you 'reinstalled'. The end of the cable has to engage with the recessed drive in the engine side.  If the fitting is not properly installed on the cable end then there can be insufficient cable length protruding to properly engage.

[A64Pilot]

Yeah take the cable off from the engine end, get a bright light and see what the drive and cable end look like.

 I’ve seen two different types of tach cable, one the cable has a slot that fits over what looks like a flat tip screwdriver and it’s not uncommon for the cable to break a piece off, the other type the cable is from memory four sided and fits into the drive, I’ve not seen that type break, but by determining that the cable isn’t turning you have trouble shot it down to the drive end.

Now that I think about it I believe the slot end of the cable goes to the tach drive while the four sided cable fits into the tach.

on edit, forget that I believe the tach cable drive end is four sided, but either way it will be obvious on removal.

[rotorman]

3 hours ago, rotorman said:

The tac cable pulled loose from its fitting at the engine side. I removed the fitting and reinstalled it on the cable. Then I screw the cable back on the engine and now the tac does not work. From the engine side I pulled the cable out of its cover and it is not broken. Next I unscrewed the fitting from indicator side and ran the engine. The cable does not turn. At the engine side the cable is screwed into the engine such that only about two thread show so I believe it is fully in. Is it possible that the cable is not engaging on the engine side? Or what else could be the problem?  

I took off the engine end fitting again and shave a bit of the cable cover so I could push the fitting further up on to the cable. That did trick. The small key at the cable end was not fully engage the tach drive.  

[PeteMc]

45 minutes ago, rotorman said:

and shave a bit of the cable cover so I could push the fitting further up on to the cable

How much is "a bit" that you shaved off?  You sure the "key" is fully into the drive or might it be prone to break off in not too many hours because of the stress just on the tip?

 

[rotorman]

I did it little by little so as not to take too muck. Hopefully I got it right.

[N201MKTurbo]

If you want to build a new cable, these guys have all the parts.

https://www.texasindustrialelectric.com/speedo.asp

They will make the cable for you too.

The owner says he makes flap drive cables for Stinson's all the time.

[cliffy]

Used to use a speedo shop for tach cables on Navajos   

Just make sure the "lay" of the twist in the cable is the correct direction  L  or  R

Edited June 12, 2023 by cliffy
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