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Old 11-24-2013, 01:38 AM   #1
Detroit Flathead
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Default 8BA Flathead fan belt widths

Will a 3/8" belt work in a 5/8" pulley?
Will a 5/8" belt work in a 3/8" pulley?
Dumb questions, I know, but I'm curious.

I currently have an 8BA Flathead using 3/8" belts/pulleys. I need to rebuild the water pumps, so I'm thinking of beginning to convert the pulleys over to the wide belts. If the pulleys are mismatched for a while, will either belt work?
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Old 11-24-2013, 08:55 AM   #2
Chris Nelson
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Default Re: 8BA Flathead fan belt widths

3/8" belts would bottom out on 5/8" pulleys. The power transmitted from the belt to the pulley is caused by the sidewall of the pulley pinching the sidewall of the belt. If it rides on the bottom, it will not transmit the needed power and will slip in short order. 5/8" belts will not work in 3/8" pulleys for much the same reason. They need to be pinched or squeezed by the pulley to transmit the power. The best result is gained by using the belt that matches the pulley. It's not a dumb question. It's only dumb if it is not asked.
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Old 11-24-2013, 09:19 AM   #3
34PKUP
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Default Re: 8BA Flathead fan belt widths

Quote:
Originally Posted by Detroit Flathead View Post
Will a 3/8" belt work in a 5/8" pulley?
Will a 5/8" belt work in a 3/8" pulley?
Dumb questions, I know, but I'm curious.

I currently have an 8BA Flathead using 3/8" belts/pulleys. I need to rebuild the water pumps, so I'm thinking of beginning to convert the pulleys over to the wide belts. If the pulleys are mismatched for a while, will either belt work?
If you are rebuilding the original pumps that have 3/8" pulleys like the rest of the system, what possible reason (that makes any sense) do you have to change them over to 5/8"?
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Old 11-24-2013, 10:13 AM   #4
rotorwrench
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Default Re: 8BA Flathead fan belt widths

The two sizes were different in more than just size in the mechanical make up of the whole drive system. The wide sheave types were used on early 48 & 49 8BA/8CM engines but in late 49 a change was made to all of the cars. Only trucks used them up through 52. Wide sheave belt systems used one belt to drive both pumps & gen so they had the sheaves aligned on the pumps. The other was to drive the fan only kind of like the 59A engines did. The narrow sheave design had one side drive a pump & the gen and the other side drove a pump & the fan. All of the parts have to follow to make it work since none of the sheaves are the same. The fans were different too. The early ones dated back to 1942 in design.

Last edited by rotorwrench; 11-24-2013 at 11:15 AM.
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Old 11-26-2013, 10:44 PM   #5
Detroit Flathead
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Default Re: 8BA Flathead fan belt widths

I learned some good info, I'm glad I asked. I assumed a wide belt would be stronger. I don't have to change it to a wide belt, but I'm investigating.
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Old 11-27-2013, 10:05 AM   #6
jimvette59
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Default Re: 8BA Flathead fan belt widths

Always use matched pulleys and belts.
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Old 11-30-2013, 08:20 AM   #7
B_man_Al
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Default Re: 8BA Flathead fan belt widths

You can throw tomatoes if you want, but I am using a 1/2 in belt as a compromise between the two. My engine is a 53 car with narrow fan and crank pulleys and wide belt truck water pump pulleys. Seems to work OK. Not ideal, but for now it gets you going. Will probably convert the water pumps to 3/8 later, if they can be done without screwing them up.
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