Bouncing tach

[The-sky-captain]

On a flight to Little Rock today I noticed my tach bouncing up and down about 100 RPM. The engine was smooth so I think it may be an issue with the cable. Have any of you guys had an issue with this and what was the solution? I've heard lubing the cable can help.

[TurboExec]

Spring in the Tach might be worn out...you can try lubing the cable that may help but otherwise overhaul, replace, or live with it.

[N207LS]

I have an acquaintance that had this occur.  It wobbled (about 100 RPM back and forth) even without engine vibration.  He was annoyed by this and his choice was to overhaul the tach or replace it.  You can buy a new tach (and have the hours set to be the same) or look at some aftermarket products.  He ended up buying the EI tach and really likes it.  Looks cool too...

Aaron

[dsimes]

I had the same condition for a 100 hours or so.  One day, about 2 months ago, I was flying along minding my own business and the most god-awful shrieking CAUGHT MY ATTENTION.  My tach was pinned, and then to zero, pinned again with awful screehing, and then zero, and then dead tach.  I have an electronic tach which of course remained steady the whole time.

The verdict was a busted tach cable.  It was a tangled mess inside the sleeve.  Its funny now, but wasn't at the time.  DS

[rgpilot]

I had that happed to my 93 with an electrical tach generator. Finally the cable broke. I replaced it with a new cable. That lasted less than 1 year and it too broke. I got a new cable from Mooney and that was manufactured incorrectly. Mooney said it would take months before the vendor could replace the defective cables. They suggested I try attaching the tach generator directly to the engine where the cable used to go. It was a very tight fit, but I got it to work. It's been 2 years and the tach has worked great.

[Jeff_S]

Had the same problem on my Warrior. Lubed the cable and it was fine.

[carusoam]

The mechanical tachs are no more complex than the old bicycle speedometers....

Try the lubrication route first....(this may have been part of the annual inspection anyway)

Had same issue as dsimes.  Usually the tach oscillated some 20 rpm or so.  One day, it was doing it's ordinary oscillation, then it wound up, squeeled, unwound, wound up, squeeled, unwound....

Then the needle fell off......  Hard to set engine power without the tach.

Cable is easy enough to replace,  at several thousand hours it may be time to replace the tach also....(also pretty easy to replace).  As usual, you may need to have A&P sign your paper.

Best regards,

-a-

[conom06d]

yeah i have this issue in my 61B. I live with it for now and just read the average of the bouncing. I'm pretty good at it now haha. I will get it lubed up when i get the annual tho since its coming up before long

[rgaines]

I Just replaced the tac.  Got one from Aircraft Spruce

[The-sky-captain]

I had my cable replaced at annual and it still has a little bounce to it, though not as bad as before. I am going to take the plunge and go with the digital tach that Horizon makes. Any reviews on this product?

[airfoill]

Bodie,

 

Call me old fashioned but I still like analog guages and I recently purchased an analog UMA electronic analog tachometer because my cable driven tach was bouncing too.  I prefer the analog because I can just glance at it and see if the engine RPMs are where it's supposed to be.  Very easy to install; just remove the old tach with cable, install the new tach to power supply and route the electronic cable to where the old tach was connected.  Install the tach sending unit where the old cable connected to the engine and that's it. 

They are also cheaper too than the Horizon tach.  I paid $455 for mine which came with the tach sending unit.

I'm real happy with mine.  Have your mechanic fill out a 337 and submit it to the FSDO.

They got high marks from Aviation Consumer magazine.

http://umainstruments.com/

 

 

[conom06d]

well...just got mine lubed and its still doing this. I guess it may be time for a new cable or tach alltogather.