Tach Issues

[Roger]

There has been a lot of talhk on here about tach's and RPM's so I thought I would relay an issues I ad last weekend.

I was flying into Key West and it was pretty hazzy, which over the ocean prior to seeing any of the islands is like flying in a dirty fishbowl (for those of you soon to go to the Bahamas).

So anyway I notice that my front engine is running 300+/- higher that my rear. So I play around with the manifold pressure, throttle the rear up, the front down, etc.... All over a period of serveral minutes, looking at my sychro needle, listening to the engine,etc... Everything seems to be running ok, but it just doesn't look right so I keep playing with it.

Meanwhile I am looking out the window and occasional catch myself turing off to the left with some bank. Back to the tach, play with settings some more look back outside, banking to the left again....but hard to see out because it is hazy, so continue to scan the AI.

After about 10 mintues of this I sit back and look over at the tach and notice something really doesn't look quite right. So I ask my wife: Does that tach look like it is sraight up and down? She of course say: no, it's tured to the left quite a bit.

So I put my hand on the face of it, turn it 20 degrees clockwise, and the rpm's are perfect ! Unbelievable! Why would an electric tach care if t was exactally vertical ?

What apparently happened is that it just viibrated itself counterclockwise, which made it read wrong. To aggravate the situation, because I was so fixated on it, I was essentially using it as a quasi AI, but it wasn't straight up and down, so when I scanned between the real AI, and the crooked tach it created a disconnect as to what was straight and level.

So back to the moral of the story: Use your ears, fuel flow and manifold pressure to make decisions on your RPM's. And don't use your tach as an AI !