The Cessna 120-140 Association Forum

I just put a new tachometer in my C-140 with C-85. The old one was not recording the hours properly. I would fly .7 or .8 and only get .3 or .4 on the tach. During the first flight it only read 2300 on TO, it usually gets up to 2500 or so. I have a climb prop so I have to throttle back to avoid going over 2575 on level off. Since I didn't trust the tach I just went by sound and throttle position for cruise. The tach then indicated 2200.

The tach is a Mitchell type 01125024 clockwise with a 2400 cruise RPM. Did I order the wrong one? Might it be the cable binding? What is the right cable length for the C-140? Thanks.

Hi Ray,

The cable is pretty short, maybe 3' 5 " or so. I'll be able to get to the hangar and measure mine in the day or two.

I'm not sure why you're focusing on the cable. It cannot turn at the wrong speed for long without breaking.

First thing I'd do is check the tach. Any decent maintenance facility should have a tach checker. If you can't lay hands on one, take it out at night under some sort of street light and see what RPM the prop appears to stop at. One of those speeds will be 1800 RPM.

My IA has a tach checker. He is out of town. My old tach started fluctuating about the same time the hour meter was lagging. I thought maybe the cable was rubbing against the housing...just a thought.

If you suspect it of rubbing, dismantle it inspect it first.

Clean and relubricate.

Reinstall and test it.

More than likely the tach itself.

It may be worth the time to check the cable.

Rick