Which shaft actually drives the cooling fan on my ?43 M? Is it the shaft the fan is mounted to or the one with the pulley at the bottom of the engine? That belt is extremely loose (PB is working on the set screw/pulley for me), and I think the slack is causing schizophrenia in the alternator. Works in the summer, not in the winter. The alternator belt is plenty tight, but if the drive comes from down below, the slippage, I suspect, would prevent the fan pulley from gaining enough RPMs.
 
The pulley on the crankshaft "the lower pulley" drives the water pump and fan which in turn runs the generator or alternator which ever you have
 
The lower one is the drive, and it should be pretty loose. Pushing hard with your thumb should push about an inch and a quarter, to an inch and a half. I know this seems unreal, but that belt is big and has a lot of surface area in contact. I have seen them go 50 years and be just fine. If the works/doesn't work issue is temperature related, I suspect the alternator not the drive. (a strobe based tachometer can show you if it slows down. You might also try a simple test with a piece of hack saw blade held on the end of the alternator rear bearing. if it is magnitized, it is at least getting field current. if little or no magnetic field, it is the alt. Jim
 
Thanks for the replies. Interesting diagnostic on the alternator?I?ll try that out tomorrow. I actually bought a new alternator this spring, but then the silly thing worked fine all summer. It sits on the bench ready to go...
 
Lower pulley does the driving. Should only be about an inch of play in the middle of lower belt. If you ever get it freed up and adjusted, make sure your set screw on threaded half of water pump pulley gets back into a groove/slot. If not, the pully adjuster will adjust itself to tight on it's own just by running the tractor. Belt will end up way to tight. Make sure your set screw gets put back right.
 
Thanks for the advice. I?m concerned the head of the screw may just crumble away (it?s a slotted screw). Do you think I should hit it with a little MAPP gas if the PB Blaster doesn?t loosen it?
 

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