cherokee tach reading low

cherokeeflyer2cherokeeflyer2
in General Discussion
Just got my AP to use an optical tach on my cherokee 140. He found the aircraft tach 100rpm low at 1000rpm and 150rpm low at 2000rpm. Is it possible to adjust the aircraft mechanical tach? New mechanical tachs cost about $450. Are the new digital tachs better? Now I know why I seemed to have low static RPM. I'm glad the engine is ok and it was only the tach...phew.

Comments

  • JoeBJoeB
    I haven't ever heard of a mechanical tach with an adjustment.

    What you're experiencing is the normal life cycle of the mechanical tach. The spring inside them seems to weaken with use - as they age they all tend to read low. A digital tach would not have this problem. Digital electronics just stare blankly at you when they fail. IMO which one is "better" depends on your faith in electronics.
  • PaulRPaulR
    There are a lot of other posts on this same question if you search the forums will find some good answers to the same question.
  • MikeLMikeL
    I had a similar experience, bit the bullet and got new Mitchell Tach from A/C Spruce, like it. I prefer the mechanical tach because it is for me easier to interpret and because mechanical tachs are better in my opinion for tracking engine hours. A digital tach records real time hours while mechanical hours are normalized by RPM. The electronic tach will cost you in the form of shortened maintenance intervals for same usage.
    >MikeL<
  • PaulRPaulR
    MikeL wrote:
    I had a similar experience, bit the bullet and got new Mitchell Tach from A/C Spruce, like it. I prefer the mechanical tach because it is for me easier to interpret and because mechanical tachs are better in my opinion for tracking engine hours. A digital tach records real time hours while mechanical hours are normalized by RPM. The electronic tach will cost you in the form of shortened maintenance intervals for same usage.
    >MikeL<

    I agree completely with Mike as I have a digital tach that came with the plane when purchased and tough to read at time as it bounces around when you change the throttle for a second or two, the mechanical ones are a lot better I think.
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