Stump the experts question of the day

Here is one for you,
Does anyone know why the inner pulley on an m38/38a1 water pump pulley is a larger effective diameter than the outer pulley.

The outer pulley has a deeper V allowing the belt to ride deeper, making it a smaller effective diameter.


you might be able to make out the difference in the attached photo

Was there a reason that there were two grooves? Are there supposed to be two belts, one for engine operation and one for something else?

If not, I'm guessing the reason for two belt grooves, one slightly longer than the other in effective diameter, maybe if you have a drive belt too loose/tight you have the option of utilizing the other groove to get your engine running without re-tuning the engine?

is it to loosen up the belts for water fording so they can slip some?

...deeper so the belts done jump off. Im not an expert though.

I'm not an expert either, I went out in the garage and looked at my '51 M38 and the grooves on the water pump pulley are the same and match the gen. and crank pulley. they were designed for duel belts. If my memory is correct the civi water pumps had different pulleys ( the narrow groove was used to run an aux pump?)

11ACR-LT said:

I'm not an expert either, I went out in the garage and looked at my '51 M38 and the grooves on the water pump pulley are the same and match the gen. and crank pulley. they were designed for duel belts. If my memory is correct the civi water pumps had different pulleys ( the narrow groove was used to run an aux pump?)

Click to expand...

Ding..Ding...Ding, I think you have it. At least it sounds good. But I'm not an expert

that smacks of a right answer. If you ran dual belts on the pully I have, it would wear one belt or the other.

I somewhere along the way, the pully was replaced.

wonder what it was intended to run? Did cj's ever have power stearing or brakes?

Some CJ units did have power steering. My 59 had a Eaton pump on its six cylinder engine.

pulley

older military jeeps sometimes had a

n air compressor fitted. or this "thing" ! (A governer)

My '52 A1 has the 4 groove pulley and 100 amp system and they are all the same. At a idle when the alternator kicks in, it pulls the engine down and you have to idle it up to keep it running. What a beast. No wonder they have a Warning of death by shock on the antenna. My '51 M38 looks to have the same belts and pulley size on the 2 belt 28 volt setup. Have you got the wrong pulley or is one worn more than the other?? My new water pump pulley I took off to put the 4 groove on is also the same. ??? John

let me shoot a better picture. Interesting mystery. The pulley looks original.

Here is what is known about the jeep.
made in 54
rebuilt carb, axles, engine, gen at fort jax in 67
military road tag on windshield 1979
clutch or stuck valve took it out of service circa 1982
stored by a civilain under a hip roof until 2005
sold to a NC sherif
traded to settle a debt in 2010
sold to me in 2010

No civilains worked on it . you can tell because nothing molested or done in non military fassion.

The pulley that has two different size grooves was used on vehicles with a govenor.

the M38 & M38A1 have two grooves, but are the same size for the generators purpose.
It is physically a large generator yet only rated at 25 amps. I talking about the factory setup.