I'm having a problem with my 27's fan belt. It's my first model T.so it's a learning experience for me. It does have a water pump and I don't know why yet. But the belt comes off the pulley while driving. One of the problems is that the fan pulley shaft is worn the pulley tapers downward towards the radiator. So I will be rebuilding the fan pulley. I was told that the crank pulley could be worn and lost its crown. With the pulley on the car I guess I can use a straight edge to see if there's any crown left. I don't have a micrometer that would open up that big. So how much crown should there be? Can someone send me a picture of a good pulley or how to measure it. When I do the repairs, I would like to repair everything at the same time.
Is there end play in your waterpump?
This older post may help.
The '26-'27 fan pulley is part of the water outlet, and the pieces have to be in good shape. You might check the position of the fan eccentric in the hub for alignment.
A worn or stretched fan belt can cause issues too.
The crank pulley should have a slight crown, and free of grease and oil too on the pulley surfaces and the fan belt.
With a water pump you have added a third pulley, so all the pulleys need to be in alignment. Most water pumps have a bolt that fits against the block to adj. the spacing of the water pump shaft and pulley, plus the pulley needs to be in the correct spot on the water pump shaft to align with the Ford pulleys.
Here are some things to measure with the straight edge.
Typical good crank pulley crown.
Many times the fan belt is too loose and it can wander. So check that too..
Flip the fan belt inside out. Does it run out the same as before or to the opposite end. If opposite I would suspect the belt. Belts run out to the high end, not the low. Pulleys with a good crown keep the belt centered. You can "re crown" most pulleys by using your drill press, file and patience.