8BA Flathead fan belt widths

[Detroit Flathead]

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?

[Chris Nelson]

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.

[34PKUP]

Originally Posted by Detroit Flathead

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"?

[rotorwrench]

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.

[Detroit Flathead]

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.

[jimvette59]

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Always use matched pulleys and belts.

[B_man_Al]

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.

[cederholm]

Resurfacing this old thread.

I have a 1952 8BA that I rebuilt years ago and I’m now getting ready to use. It was a truck motor. Maybe a silly questions but how can I be sure I’m ordering the correct width belts? I assume 5/8th. Just measure the pulley opening?

Thanks,
Carl

[solidaxle]

You are on the right track for the width. To save you from going back and forth to the auto store numerous times. For the length, you can use a small rope and buy a couple of sizes each way from what you think it is.

[B_man_Al]

Does anyone know if the wide belt pulleys on the F1 water pumps can be replaced with the narrow belt offset pulleys from a 1953 ford passenger car (original 53 car water pump pulleys). I would like to convert to the 1953 ford car belt system with the back pulley driving the generator and L pump and the front pulley driving the fan and R pump. My crank pulley is narrow belt as the whole engine came from a 53 ford car but has been installed in a 48 F1

[69a]

There is no problem using a narrow belt with the wide pulley water pumps as they have very little resistance. I am using the truck wide (8RT) pumps and cast iron crankshaft pulley, but my alternator pulley is narrow so I have been running the narrow belt for 40 years. I have had the intention to get the alternator pulley machined for the wide belt, I'm now on my second motor and still haven't gotten around to it. The first symptom would be the alternator not charging because the belt is slipping on the crankshaft pulley. I have an electric radiator fan and when it kicks in the amp meter shows a healthy charging rate. The belt still has sharp corners on the inside and shows no signs of wear.

[B_man_Al]

I have an annoying vibration at around 2000 RPM (40mph) . I wonder if you ever noticed that and if it might be due the narrow belt bouncing around in the wide pump pulleys?

[19Fordy]

If you "GOOGLE". "How to select an auto fan belt?" lots of very helpful info. appears about what you are asking. Really helpful.

[Eagle43]

I've never heard of a 3/8 size belt. They come in A (1/2") and B (5/8) as far as I know. You can probably buy them cheaper at a farm store.

[marko39]

Originally Posted by Eagle43

I've never heard of a 3/8 size belt. They come in A (1/2") and B (5/8) as far as I know. You can probably buy them cheaper at a farm store.

A 3/8 belt is known as a 3L while a 1/2 belt is a 4L and so on. Unlike A or B belts the L belt sizes are their true length.

[Eagle43]

Thanks. Learned something new today.

[V8 Bob]

One thing that hasn't been brought up is the '50-'53 left and right narrow belt pump pulleys are not the same diameter, and must match the cast iron crank pulley with the two different diameter sheaves, to have the pumps run at the same rpm. I have never found the reason(s) for the narrow belt crank pulley design, but guess it was to alter the fan and/or generator rpms.

[19Fordy]

Thanks Bob, I didn't know the pulley dias. were different.

[leon bee]

Is that just cars?

[Flathead Fever]

Like has been said, a belt is designed to ride on the sides of it, not the bottom of it. It has twice the slipping force riding on the sides, the bottom of the belt is not supposed to be touching the pulleys. I see people make that mistake on flatheads all the time, a narrow belt on a wide flathead pulley, it will spin the parts, but it's not correct. All cars that use "V" belt are made to ride on the sloped sides of the belts.

If I remember correctly the '49 8BAs still had the wide belts and then Ford switched to the narrow belts in '50. I keep a bunch of old cut up belts for engine projects. I wrap the "correct width" belts around the pulleys and mark their lengths where I want them. Then I measure the cut belts and have the parts store get me knew ones the exact length I tell them I need. It works out really well. By the time I tighten it, it's in the middle of its travel. They'll stretch a little bit after they have been run awhile, so you always want to have extra adjustment for them.