calibration of tachometer

[drturf0]

ok i have a utometer 2888 diesel tach(pick up on alt. ) and the instructions say to calibrate i need to know the pulley drive ratio and the number of poles on the alternator ,and also states to calibrate at highway speeds to get proper readings well i've never had a tach in this truck so how do i get proper readings ,i don't know what it turns at certain speeds ,can anyone help me with calibration of this tach?

 

[Lil' Dog]

My ol 89 had an alternator tach and I had to calibrate it as well after an alternator change. You need to get some measurements to determine the calibration:



1: Drive pulley Dia. (Crankshaft)

2: Alt. pulley dia.

3: Diff Ratio.

4: Tire Size.



After that we will be calibrating your speedo as well LOL. I have an idea of what and where for the speed Vs. Rpm.



I have a phototach at work for tach calibration. All I need to do is stick a piece of reflective tape to the crankshaft pulley and aim the probe at it. Then tweek the tach to match, too bad you're so far away. .



We can figure it out. .



J-eh

 

[drturf0]

see if this sounds right 31. 5" tires 3. 54 gear . 73 overdrive ratio @60 MPH 1650 rpms.

 

[Lil' Dog]

Pretty close.

Just doing the math it comes out at 60 MPH that its around 1653 RPM, assuming true lockup in OD.



Wheel speed for 31. 5"Dia @ 60 MPH = ~640 RPM

640 x 3. 54 x . 73 = 1653RPM



Can't get any closer than that!!!!!#ad




J-eh

 

[drturf0]

thanks for your help ,just one more ? how was your tach mounted?