Gene:
At full power my tach only reads 2,100 RPM. I used a digital tach and found that my tach is reading 300 rpm low; i.e. should be reading 2,400 RPM. Now my question is, does anyone have a good tach for a 1966 A23/24, 200HP I0360 Lycoming eng? If not, how about a good rebuild or tachometer overhaul shop? I would like to keep the Beechcraft logo, but I could live without it.
Bob Steward, A&P-IA:
The choices are a new Mitchell tach for about $175 (you’ll have to have it range-marked), or to repair the one you have. There is also the option for a (very expensive) electronic tach. Here are some links:
http://www.aircraftspruce.com/menus/in/tachometers.html
http://www.aircraftspruce.com/catalog/inpages/mech_tachs.php
Airparts of Lock Haven PA is a source for overhaul. $128 to OH and Yellow Tag it.
http://www.airpartsoflockhaven.com/
http://www.airpartsoflockhaven.com/c5.html
They can also do other instruments like the engine OT, OP, and the fuel
level gauges.
Editor: A few more thoughts:
Most of the older tachs have an oiling port on the back. They never get lubricated. If the bearings dry out before they fail, the tach may read high. If they have oil but it gets gummy, the tach may read low before it fails. If you can afford to take the time, you can locate the oiling port and apply some LPS-2 spray oil, then fly it a while to see whether it recovers. It may take a couple of tries. If it frees up completely, you should follow up with a dose of true instrument oil, which would last a while. Otherwise you will need to lube it with the LPS-2 about every 40-50 hours.
Most of the later replacement mechanical tachs are plastic, with much less robust internal parts. I have seen failures reported in as little as 400-500 hours. If you must ultimately choose between overhaul or new, and you have one of the solid original units, my recommendation is to have it overhauled. That will also retain your original range markings and the Beechcraft name.
There is also a company that will overhaul your tach and install a new face, with the Knots on the outer scale rather than the inner scale. I have to confess that I do not have their link on this laptop, and I’m not finding them in searches. Perhaps someone will read this and will forward the info on that company.