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Old 04-22-2014, 09:01 AM
SMN3D SMN3D is offline
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Join Date: Aug 2013
Location: Portland, OR
Vehicle: 1984 245 D24 M46 (converting to D24T auto), 1982 244 (installing missing D24 and M46 from wagon)
Posts: 13
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I measured the diameter of the pulleys on the D24, and this is what I got:
Crankshaft: 15cm
Alternator: 40mm

From a few minutes of research online, I found the diameters on the Mk1 VW diesel to be:
Crankshaft: 14.9cm
Alternator: (varies, either 30mm, 40mm, or possibly 70mm)

Since I wasn't using a micrometer (and didn't remove either the lower shroud or the radiator), I'm willing to guess my measurement of 15cm is pretty close to the specified 14.9cm of the VW Mk1 Diesel. :-)

According to the incomparable regcheeseman at a posting here:

http://www.vwcaddy.com/archive/index.php/t-4749.html

"The original spec of the W terminal I recieved was incorrect, instead of 25 pulses per rev, I've seen quotes of 14.5 pulses per rev quoted elsewhere.

There are at least two pulley combinations to drive the alternator so this can compound things further.

However the degree of calibration available on the standard tach is considerable and should be able to cope with adjustment btween theese variables."

So when I get some time in the next few days, I'm going to wire up the tach exactly as specified in regcheeseman's schematic, and then test it out on the bench with a drill of known RPM, use the 14.5 multiplier, and calibrate the tach on the bench using the pot already on the PCB. I'm not looking for super accuracy here, and I can always pull the cluster and recalibrate later (hopefully not snapping the speedo cable nut in the meantime!)

I will keep you up-to-date, and if all goes well, there will be an easy way (if you can solder and have the correct W-terminal alternator) for anyone to get a functional tach into our beloved volvos with very little cost (and how it came from the factory)...

Scott
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