Technical Flathead pulley and belt help

Hello all
Just staring to figure out my fan belts with the pulley and fan set up I have. What size dose the flathead usually use for fan belts my power gen alternator and water pump use 5/8 but a 5/8 belt almost bottoms out in the crank shaft pulley


A 3/4” belt seems to fit best in the crank and fan but rides too high on the water pumps/ alt

I thought that the flatheads either used a 3/8 or a 5/8 belt. I’m not sure of the origins of the crank pulley( on pice cast) or the fan as the person I purchased the engine from included them.

What am I missing was there a 3/4” fan assembly for these engines or do the 5/8 belts just run that low in the grove
Thanks


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I just run a 5/8" belt on mine. It does fine.

 

Get a look at the bottom of the belt as it goes over the pulley. If the bottom of the belt is not touching the bottom of the "V" of the pulley, you are OK. The belt is not suppose to bottom out on the pulley.

 

You've probably got 49 Merc or truck crank pulley and fan pulley, and regular car pumps. The Merc and truck used wide belts, the cars used the narrower.

 

Thanks everyone
The 5/8 belt has about 1/16-1/8” before it bottoms. I suspect you are right about the Merc/ truck pulley and fan. Think I might use the larger belt on the fan so it looks corer and try running the 5/8 belt for the pumps and Alternator. Maybe keep a eye out for a standard pulley and fan
Thanks Rob


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3rd pic down, is close to how belt should sit on pulley.
Top two pics don’t look to be correct.

 

You have a truck fan and I think a Merc lower pulley. The trucks used an 11/16" wide belt for the pumps and generator.....pretty hard to find now, the 5/8" should work there. I use a 3/4' belt for the truck fan.

 

I figured I should update this with my final resolution.
Lesson 1 don’t trust anyone at Napa to order belts by Size

Turns out my crank pulley is the one with two different sizes 5/8 for the water pumps and hen and 3/4 for the fan belt never noticed this until I had the balancer off the other day

Turns out I needed a 37”x3/4 fan belt and a 57x 5/8 belt for the water pumps and my off set generator