Tuning the Tachometer

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August 2006 --

This is a cool infrared strobe tachometer, that I bought to help me tune the tach that's driven from my alternator.

My new engine came with a little 50A stock alternator with internal regulator, and I didn't buy an upgrade option because I have a perfectly good Ample Power high output alternator from my old engine, and a perfectly good Xantrex Link 2000R voltage regulator.

This little tool cost $80 from Harbor Freight (part number 41727-0VGA). Of course, it's an $80 tool that I'll probably never use again, but maybe it'll help me make a few friends in the future.

You stick a little piece of reflective tape on the crankshaft pulley, so the tool can get a good mark.

The tape doesn't need
to be this wide,
but this works.

I had a few moments of fun
trying it out on household fans,
and things like that.
It doesn't really need reflective tape,
but it does need a high contrast source.

I tried aiming it at my cat's tail
when I was annoying her,
but couldn't get a consistent reading.

The tool shoots out a red infrared beam to help with aim, even when you're standing on your head.

I was just taking a picture
in this example.

In real life,
one would have the red spot hit
the reflective tape.

Yes, I mounted my panel upside down and flipped a few gauges over. It makes perfect sense on my boat, as I want the switches up high and protected by the cockpit seat, but want to see Oil Pressure, Temperature and RPM from the helm without having to bend over.

For the tach, I'm really interested in RPM between 1K and 3K, so having the meter upside down is a lot easier to see when standing at the helm.

My Tachometer has a big pot switch on the back that allows it to adjust to match the number of rotors in the alternator. Then there's a little hex key fine tune adjustment knob. There's no point getting into finer detail at the moment, but I want to mention that the instructions say that one should be very careful when turning the "fine tune" adjustment. In my experience, that means that you can break it.