Sluggish tachometer

[russfarris]

Here's one I've never seen before - I help a friend maintain his 1960 172, because he's not that mechanically minded and it's virtually the same as a 170. Very nice airplane with only 1,500 total time.

His tach lags behind actual engine RPM by a few seconds - you set 1,700 Rpm for run-up and then it creeps up to around 1,900 indicated. The actual RPM doesn't change, verified by my hand held-tach. The aircraft tach is accurate and smooth, but never seen one lag like this before. My only idea is perhaps the drive cable needs to be removed, cleaned and lubed.

Any other ideas on this? Russ Farris

[GAHorn]

Mechanical tachs do not "drag" or "lag" because of cable-friction. They do so because of their meter-movements which have excessive drag. (They operate via rotating magnets or by friction-clutches. When those mechanisms begin to fail, usually thru wear but sometimes due to improper or lacking lubrication,...they drag. It sounds like its time to replace your friend's tach, or have it repaired.)

[russfarris]

Now that you mention it George, I do seem to remember something about magnets in the tach. It's defintely the original one. It's weird flying it, almost a turbine-like lag. Russ Farris

[GAHorn]

... It's weird flying it, almost like a turbine-like lag. Russ Farris

So what's YOUR problem, Russ?