is there a way to make a 85gm alt work on ford tract

marlin54

Member
bought a 55 ford 800 with 4 cylinder. There is a 1985 gm 3 wire alternator with internal reglulator mounted on it . But I don't know if there is a way
to make it charge since I think the gm alternator doesnt start to charge untill it hits like 2,000 rpm.and a 4 cly tractor usually tops out a 1,500 .
and I would like to see if there is a way to make it charge a low rpm . I dont want to change the pulley as that is alot of work and it would have to be
alot smaller and dont think thats possible . anyone have an idea without having to get a gm 1 wire. ? thanks.
 
We have put similar Delco alternators on many of our tractors. Since the pulley on the alternator is much smaller than the crankshaft pulley, the alternator is turning at least 2X as fast as the engine. We haven't had any problems with our conversions. There are some pulley options for that alternator. In some cases I use a double wide alt pulley and run a single belt on the outer pulley groove. Just put the belt onto the groove that allows the belt to run straightest. The smallest pulleys I've used are about 2" diam, and the biggest are about 3.5" diam. The smaller the pulley, the faster the alt spins.

I have used the one wire conversions on some of the tractors. There seems to be quite a difference in the RPMs needed to excite the alt. Evidently there are different regulators used by other rebuilders. Once the alt is excited (high RPM) it will continue to produce charge current even at an engine low idle. I prefer the 3 wire conversion as the excite juice comes through the 3rd wire. So the engine does not have to be revved up to start the alternator. These alternators are easy conversions for small tractors like the Farmall H. the 8N Ford, and on up through our Ford 8000, 9000, TW 10 and just about every other make. If you can mount the alternator so that a V belt runs straight, then you have done the hard part. They are very reliable compared to the generator system they replace. And they are common enough that they are relative low cost.

Good Luck

Paul in MN
 
If it is the common 10SI or 12SI GM 3 wire alternator with 2 pin edge plug, the #2 pin can loop down to large output stud. #1 can go to output side of charge light if it has one. If not through a diode, resistor, or lamp to the output side of ignition switch.

This assumes that your alternator is in good working condition.

Alternator should spin about twice the engine rpm, so speed should not be a problem with 3 wire or 1 wire alternator.
 

1 wire Delo has to be reved some to excite
3 wire when properly wired will start charging as soon as the engine starts.

FYI 800 Ford has a pto operating speed of 1800 rpm and those engines will rev to 22-2400 rpm.
 
[b:785bd0c682]Testing Feasibility Of 3-Wire Alternator Conversion[/b:785bd0c682]

If your alternator has a rubber plug covering the spade terminals identified as 1 and 2 then jumper #2 spade terminal to charge stud on the back of the alternator. With engine running at mid throttle, leave first jumper in place and momentarily jump #1 to the charge stud. If this makes charge voltage come up, then permanently wire #2 spade terminal to the charge stud. Run a wire from the key switch through a 194 or similar lamp to the #1 spade terminal.
 

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