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Belt alignment

I am having a bitch of a time getting the belt alignment straight.

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Joined: Fri Aug 12, 2005 5:45 pm

Belt alignment


Post by panz4ever » Wed May 23, 2007 10:49 am

Running a belt primary w/ tin inner and outer on my chopped 50. After reassembly I am having a bitch of a time getting the belt alignment straight. Anyone with some info/tips/trickes to get it right would be appreciated.
Know it will take some spacing on the front motor sprocket, but the spacer I had before I took the motor down for the rebuild left some residual where the belt was rubbing. Would like to get it right once and for all.
Seems like there should be a way to takes measurements (like on the 65 and up with aluminum inner) to make it clean and simple and determine correct spacer needed.

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Re: Belt alignment


Post by Panacea » Thu May 24, 2007 12:27 am

I had problems getting the belt to align on my 51, In fact the problem went way back to 93 when I was helping the previous owner try to alighn it. He never did get it right. After I got it, I used a strait edge accross the clutch basket, trying to set the tranny so the pulleys both measured back off the strait edge the same distance. I finally got the problem fixed by takeing the frame to a shop that had fixtures to check the mounts for correct location, He wound up making an adjustment in the rear bracket mounting holes, which worked perfectly! Now it runs nice and strait. Mike

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Re: Belt alignment


Post by Kuda » Thu May 24, 2007 8:34 pm

Here's a little something I wrote up for another guy with the same problem, might help...

So, what's the problem? Rear pulley too high? Too low? If it's too low, that's an easy to fix, just need to shim the whole trans plate up a bit. If the front pulley is too far "in" compared to the rear (rear pulley protrudes more than front), then it gets a bit tougher, as the older pans use a tapered motor shaft so they can't be shimmed out like a splined shaft can. Only choice there is to either egg out the holes in the trans plate to move the trans in a bit, or buy a trans plate with an offset. Now, if one of the pulleys is tipped up (outside edge of the pulley is higher than inside edge, so the pulley is running at a slant) then shimming up or down on one side of the trans plate will take care of that.

What you're shooting for is for both pulleys to run true to each other, which means both are the same distance from each other on the inside of each pulley and the outside of each pulley, and running at the same height in comparison to each other (centerlines lined up). On a 1 1/2" belt, that's not too hard to do. But a 3" belt is a lot tougher, 'cause even a little bit of difference and you'll be chewing up those high dollar belts in short order. To be honest, I really don't recommend a belt that wide on an early pan 'cause of the older style shafts. All that extra weight and leverage of a 3" pulley is asking a lot of those old shafts and cases. <shrug> But that's your call, of course. But getting it trued up perfectly and keeping proper tension when it's warm is gonna be critical if you don't want to burn up bearings or eat belts. I'd also recommend a "pulley saver" or "even pull" trans tensioner for that set up. Basically, it replaces the single sided bolt and strap on the right rear of the trans using a strap that captures both front trans bolts and uses the front trans plate mount holes as an anchor. Two studs with double nuts on each side of the trans allow you to move one side of the trans independent of the other, so you can line up the trans laterally. They're cheap, like $20, so it's a fairly cost effective way of doing it...

In terms of actually checking pulley alignment, best way is a piece of plate glass, a little less than 3" wide and just long enough to drop between two teeth on the pulleys. The ends have to be 100% square to each other and the sides (prefect rectangle). Drop in in there and tap on the inside edges of the glass. If it rocks (lifts up one edge) the pulleys aren't lined up right (centerlines don't match). On the front and rear edges, if one side of the glass isn't in the same location on the "teeth" of the pulley, then they're not parallel to each other...

Couple other things to think about: if you're really gonna ride this thing, Primo and BDS pulleys are really only good for about 30-40K miles, on the very outside. They're aluminum, so they wear out pretty quick. Supermax pulleys are made of plastic, so they don't get as hot and wear a lot better, usually outlast the bike. Also, big belts on metal pulleys get hot. REALLY hot. And they tighten up when they're warm, so always check belt tension after 100-200 miles to really be sure you're dead on. If you tension it cold, it'll get so tight you'll either snap the belt or destroy bushings/bearings once it warms up. Hope all this blather actually helps in some way...

'49 panchop

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Re: Belt alignment


Post by panz4ever » Sat May 26, 2007 7:17 pm

Kuda, thx for tip, I'll definitely give it a try...

Panacea, if I can't get it right I am going to take it to a shop I have do my engine build ups on my pans over the years. Good wrench and one of only two that works on pans in my area of Kalif.

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