Crowns on Pulleys

Subject: ABOUT CROWNS ON PULLEYS
Date: Sun, 24 Sep 2000 09:33:59 -0700 (PDT)
From: JUDITH COTTER 

Hi John Culp, 

Wholly Cow! Another use for duct tape!

You can put a permanent crown on the pulley yourself fairly easily with a little patience. But, first you must determine what the original purpose for having a square machined profile on the flywheel is for. If it has an important function, you sure don't want to destroy it! Just off the top of my head, I'd say the flywheel is machined square because that is the fastest cheapest profile to cut on a lathe, any different profile requires more time (production $) using a profile follower attachment on the lathe. If you will forever be running flat belts on the flywheel, then go ahead and machine a crown on it. The next part is to determine what is the best crown profile to put on it. The sharper the crown angle the more stable the flat belt will ride, but because of longitudinal flexing (the belt being forced to assume a spherical shape) the belt life will be shorter. It is a compromise. Find a crowned pulley if you can, and copy its profile if you are unsure what it should b! e. Cutting the profile is easy with a hand held buffer-grinder motor with the engine running and NOT VIBRATING all over the place. Use a M.K. Morse type 27 7"x1/4" metal grinding disk or equivalent. VERY IMPORTANT! COVER THE CRANKSHAFT SEALS TO KEEP GRIT FROM GETTING IN THEM! Cover anything else you can think of to keep the grit out, it will fly around like it was a sandblaster. Another use for duct tape and cardboard! The middle of the flywheel perimeter doesn't need any metal removed, so just concentrate the grinding on the edges, making them a nice curved symmetric bevel. Start with a light touch, don't go hogging away metal rapidly as that will produce an out of round cut. Another thought is to plaster JB Weld epoxy on the flywheel, then sandpaper its profile to the crown shape the same way as above, that way you won't destroy the original flywheel surface in case you ever want it back. Just make sure you prep the surface well with coarse sandpaper so it sticks. If you! try that, buy enough to do it in one sitting, and think about some way of molding it so you don't have to sandpaper it a lot. You could make a spreader cut to straddle the flywheel width and have its profile curved like you want. Make it out of sheet metal from a tin can or 0.010" aluminum sheet flashing, or whatever.

Modern flat belts are made from polyurethane, nylon (slippery), fiber glass reinforced neoprene or chloroprene rubber, polypropylene (slippery and light duty low temperature only).

The polyurethane type is the easiest to use because you can cut and glue it yourself, the rubber needs a vulcanising process just like a hot patch tire repair. I don't know about nylon except it is hygroscopic and stretches in humid weather, and polypropylene has to be heat welded. Good old leather and canvas are great, too, but don't last like the synthetics, and leather nowadays costs big bucks. Consider buying large diameter non-steel wire reinforced rubber hose then slitting it lengthwise to flatten it. It can be glued with Camel, Monkey Grip (or whatever brand you have on the East Coast) tire patching cement, preferably hot patch. Rubber is best prepped for gluing by lightly grinding it with a wire wheel to get all traces of parting compound off of it. Getting hose to lie flat might be a re! al pain, though, I wouldn't spend a lot of money on it. Rubber can be "ironed" but it has to be really hot, like maybe 350 F.

I remember the big long belts at the blacksmith shop flapping and slapping, with the stapled connections smacking rhythmically. That was last year, actually! Our local blacksmith shop is owned by my best buddy's cousin, and he has kept it old fashioned in ways where it doesn't interfere with making a living.

I hope this helps, not all complex endeavors are difficult.

 
Work and play safely,

Richard Allen

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Subject: Re: ABOUT CROWNS ON PULLEYS - why do you need it???
Date: Sun, 24 Sep 2000 10:16:24 -0700
From: Paul Pavlinovich 

Align the pulleys so when you sight along the centre of one of them you see the centre of the other one. They should be positioned in such a way that there is slight tension on the belt enough so it does not slip and burn, but not so much that it wears your bearings.

Always run the same surface to the pulley (this does not matter with a new belt, and it can even be advantageous to belt life to swap it after every run for even wear) so that the cracks in the belt surface do not get any worse.

I also do not use any kind of belt glue, grease, or soap on my belts for operation. Once a year I attack them with "Renapur" (an English leather treatment - I use this stuff on all of my leather, belts, shoes, coats, furniture - magic stuff the leather really drinks it in and stays supple - added bonus is waterproof boots - if you have not guessed yet I love the stuff :)

Regards
Paul