FLAT BELTS & PULLEYS

Seems like I read somewhere, maybe in GAS ENGINE MAGAZINE, that when you are setting up flat belts and pulleys that the drive pulley should be flat, and the driven pulley should have a crown on it to make the belt stay on. Is there any truth to this? I have not had a lot of experience with flat belt drives and I am just curious.

David M.

I have never seen a flat belt pulley drive or otherwise that did not have a crown on it. This causes the belt to always stay at the center of the pulley if they are properly aligned to began with. Even a round leather belt will stay centerd on a crowned "flat" pulley. I ran a washing machine many times this way.

I have several engines with "flat" pulleys on them and they all look original, but I have a six horse Witte with a pulley with a crown that doesn't look original. I was wondering if it mattered one way or the other. The pulleys on my pump jacks all are crowned, and so is my Fairbanks-Morse 32 v #3 generator. Do both pulleys need to have a crown???

David M.

Both the driver and driven pulleys should be crowned. The belt will stay in the center on a crowned pulley. Flat pulleys are used for driving tight and loose pulleys. Tight and loose pulleys are two pulleys right next to each other on the same shaft, one is tight on the shaft and the other is loose in the shaft. The driving pulley will be twice as wide as each of the driven pulleys so that the belt can be shifted back and forth between the tight and loose pulleys. The driver is flat so that the belt will track on the tight and loose pulleys.

The governing factor of using flat or crowned pulleys is what you intend for them to accomplish. If you want the belt to track centered, even with some slight misalignment, then both can be crowned. If for any reason, such as a tight and loose pulley as a clutch on a piece of equipment or lineshaft, the DRIVING pulley should be WITHOUT a crown and twice or more the width of both driven pulleys combined, and the DRIVEN pulleys should both be WITH a crown to assure proper centering of the flat belt. [This is a bit redundant of an earlier response.] A crown can be machined on a flat pulley if desired.A 2 degree taper, of course meeting at the center of the pulley face, will be adequate. After machining, use a file to smooth and round over a little the very center where the 2 tapers meet.If you have good alignment, both pulleys can be flat with the belt tight. On canvas belts, a small amount of steam cylinder oil makes a good belt dressing. On leather belts, a small amount of castor oil will help dress the belt. Let either one "run in" awhile before putting on any more. Used sparingly, both will help keep your expensive belts in good shape for a long time.

Many thanks y'all

Lot's of good information here!!!

David M.

Excellant advise. If you can get a I.H. "M" engine owners manuel (or buy one for a few bucks) there is a very good section in the rear of the book on pulleys and belts which is easy to understand and has diagrams. Gook luck,,,,,Carl