Tachometer Calibration

berrybus1 · August 16, 2016, 03:50:20 PM

We have a 1980 MCI9 with a belt driven alternator (I'm assuming its original to the bus) and am trying to calibrate the Tachometer. Does anyone know how many magnetic poles are in my belt driven alternator. The questionnaire in the tachometer calibration brochure gives me the options of 8, 10, 12, 14 or 16 magnetic poles.

Thanks again, this group has baled me out of trouble more than once, twice, maybe a hundred times!

Jim

sixtyseven · August 16, 2016, 11:41:23 PM

When I asked that same question, nobody had the answer. We'll see what happens this time

What I ended up doing was buying a laser tach so I would know the correct rpm, then did calibration trial and error to set my tach. good luck.

berrybus1 · August 17, 2016, 04:37:40 AM

Sixty seven, that's exactly what I was going to do. I had talked to some very knowledgeable guys and they didn't know that answer either. Anyway, if I come up on that answer I will post information to the forum.

sixtyseven · August 17, 2016, 07:07:01 AM

That sounds good. The nice thing about using the laser tach is you know your dash tach is dead on when your done calibrating, also you can check your governor speed setting while you're at it

Frank @ TX · August 17, 2016, 09:58:02 AM

Hi berrybus1
I used a laser tach also.
But now I wonder why.
If you idle the engine it will be about 550 RPM , at fast idle it will be about 1100 RPM.
Could you adjust the tach so this numbers read at those two idle settings.
The reading error will be very small at highway speeds.
Give it a try.
Frank

Andy T · January 12, 2017, 04:37:29 AM

Sorry I havent been on in a while. If you search Ametek 900 Calibration, It will give you a list of all the calibration codes needed for different flywheels for direct reading sensors. I'm not sure of your specific code, the pulley size would matter also. There is also a chart for calibrating speedometers also.

B_K · January 12, 2017, 07:10:30 AM

FYI your belt drive alt. is NOT factory set up on a 1980 MC9! That would have been a gear driven 50DN off the back of the engine.

Sorry can't help with the tach adjustments

BK

Lin · January 12, 2017, 10:03:29 AM

We did ours with a laser tach some years ago. Cheap and easy plus you get to keep a nifty new tool.