davidrayner
XS650 New Member
There needs to be at least one lip or flange on both sides of the belt. Assuming there is only one each side, they can be both on one pulley or the other, or one on opposite sides of each pulley. The bike in my original post is like that. The trans pulley will have a flange on the outside (not fitted when the pic was taken) and the wheel pulley has one on the inside. The two others have a trans pulley with flanges on both sides and none on the rear pulley.
The pulleys must be perfectly aligned or the belt will wander off. Once you have the belt on and tensioned reasonably tight, you keep tensioning while turning the rear wheel by hand a few revolutions each time you adjust the tensioners on one side or the other. Do a little at a time and by the time the belt is tensioned correctly, you should have the belt running true and not wanting to wander off or rub hard against the flange on either side. If the belt ends up too tight by the time you get it running true, loosen the adjusters, push the wheel forward a little, and start again. All my bikes have custom swingarms which incorporate adjusters that can move the axle both backwards and forwards making this job much easier. Nice to have but you don’t need to go to that trouble.
Not only do belts need perfect alignment and tensioning whereas a chain can get by with ‘close enough’, but one thing they will not tolerate is debris getting between the belt and pulley. So, you must make a cover for the top side of the lower run to stop crap thrown up by the tyre landing on the toothed side of the belt to then be fed into the pulley but the top run needs no cover at all (see pics of belt cover on bike with panniers – they make it hard to get a good shot but best I could do).
I’ve sent this info to two other people (both in the US) who’ve done it and as I requested, they sent pics of their bikes to me. The first is the red Special. The owner was apprehensive about using a 21mm belt and so used a 36mm belt which he cut down to 30mm, necessitating a notch to be cut out of the swingarm to accommodate the pulley and filled with a piece of right-angle steel welded in (see pic of swingarm with notch cut out but not yet filled). The second is the blue chopper that’s owner is in love with white-wall tyres (see before and after pics). He used a 21mm belt. Both bikes have flanges on both sides of both pulleys. Is a 21mm belt wide enough? My first one used a 36mm wide Poly Chain belt but I made a new swingarm to suit (see pic of bike with skulls & flames paint job – getting a new exhaust). That was at least 15 years ago and since then, Gates has released their Poly Chain Carbon GT belt (they have blue teeth – see pic of belt hanging on handlebar) and a 21mm Carbon GT has a greater tensile strength than a regular 36mm Poly Chain. My other bikes have 21mm belts. There is also a fellow here in Australia who has fitted a belt but with little or no help from me. It’s the red street-tracker and it has a Yamaha Radian swingarm.
As for my four bikes, three have had Ivan Hoey’s high-ratio primary gears fitted which means I need a larger rear pulley to compensate so they have a 40:90 ratio and the next longer belt. That gives an overall ratio a little taller than stock which is like using an 18t sprocket on the trans or a 32t on the wheel. When I regeared the first one (the one with the 36mm belt) I bought 21mm items. The second and third had 21s from the start and the forth bike is yet to be done. It’s a chopper so I may make the swingarm longer and use an OD 5th gear in it which means I’ll need an even bigger rear pulley and an even longer belt. We’ll see. To save some money on the third bike, I used both 36mm pulleys from the first bike, cut down to 21mm as it’s the only one with stock primary gearing and there’s a reason for that that’s not relevant here and because the gearing remains stock, I’ll probably put an OD 5th into it. All four also have cush-drives but that’s another story entirely although I’ve included a video if you’re interested. Most people wouldn’t bother, but I’m not most people. No, there’s something seriously wrong with me.
I won’t lie or sugar coat it, this is not an easy thing to do. You must have at least some mechanical and engineering talent to attempt it. If you have that, I’ve given you enough to go on and if you don’t, nothing more I could say or do will help you. As for me, I’m neither a mechanic nor an engineer. I was a painter back in the ‘70s (I’ve painted every bike I’ve owned) and later became a train driver (railroad engineer if you live in Nth America) but I enjoy playing with machinery and wondering how I can make it better.
BTW, the 40t, 21mm rear pulley in the pic of me holding it fresh off the mill is now surplus to requirements and is for sale. I’m asking the cost of a new pulley from Gates and you get the machining and gold-zinc plating (as shown in pic of it next to the unmachined 90t pulley) for free. If you want it, email me davidrayner23t@gmail.com I have no idea how to insert pics here so email me and I'll send them to you. Ask questions about any of this if you like and as with the red Special and blue chopper, please send pics if you go through with it.
The pulleys must be perfectly aligned or the belt will wander off. Once you have the belt on and tensioned reasonably tight, you keep tensioning while turning the rear wheel by hand a few revolutions each time you adjust the tensioners on one side or the other. Do a little at a time and by the time the belt is tensioned correctly, you should have the belt running true and not wanting to wander off or rub hard against the flange on either side. If the belt ends up too tight by the time you get it running true, loosen the adjusters, push the wheel forward a little, and start again. All my bikes have custom swingarms which incorporate adjusters that can move the axle both backwards and forwards making this job much easier. Nice to have but you don’t need to go to that trouble.
Not only do belts need perfect alignment and tensioning whereas a chain can get by with ‘close enough’, but one thing they will not tolerate is debris getting between the belt and pulley. So, you must make a cover for the top side of the lower run to stop crap thrown up by the tyre landing on the toothed side of the belt to then be fed into the pulley but the top run needs no cover at all (see pics of belt cover on bike with panniers – they make it hard to get a good shot but best I could do).
I’ve sent this info to two other people (both in the US) who’ve done it and as I requested, they sent pics of their bikes to me. The first is the red Special. The owner was apprehensive about using a 21mm belt and so used a 36mm belt which he cut down to 30mm, necessitating a notch to be cut out of the swingarm to accommodate the pulley and filled with a piece of right-angle steel welded in (see pic of swingarm with notch cut out but not yet filled). The second is the blue chopper that’s owner is in love with white-wall tyres (see before and after pics). He used a 21mm belt. Both bikes have flanges on both sides of both pulleys. Is a 21mm belt wide enough? My first one used a 36mm wide Poly Chain belt but I made a new swingarm to suit (see pic of bike with skulls & flames paint job – getting a new exhaust). That was at least 15 years ago and since then, Gates has released their Poly Chain Carbon GT belt (they have blue teeth – see pic of belt hanging on handlebar) and a 21mm Carbon GT has a greater tensile strength than a regular 36mm Poly Chain. My other bikes have 21mm belts. There is also a fellow here in Australia who has fitted a belt but with little or no help from me. It’s the red street-tracker and it has a Yamaha Radian swingarm.
As for my four bikes, three have had Ivan Hoey’s high-ratio primary gears fitted which means I need a larger rear pulley to compensate so they have a 40:90 ratio and the next longer belt. That gives an overall ratio a little taller than stock which is like using an 18t sprocket on the trans or a 32t on the wheel. When I regeared the first one (the one with the 36mm belt) I bought 21mm items. The second and third had 21s from the start and the forth bike is yet to be done. It’s a chopper so I may make the swingarm longer and use an OD 5th gear in it which means I’ll need an even bigger rear pulley and an even longer belt. We’ll see. To save some money on the third bike, I used both 36mm pulleys from the first bike, cut down to 21mm as it’s the only one with stock primary gearing and there’s a reason for that that’s not relevant here and because the gearing remains stock, I’ll probably put an OD 5th into it. All four also have cush-drives but that’s another story entirely although I’ve included a video if you’re interested. Most people wouldn’t bother, but I’m not most people. No, there’s something seriously wrong with me.
I won’t lie or sugar coat it, this is not an easy thing to do. You must have at least some mechanical and engineering talent to attempt it. If you have that, I’ve given you enough to go on and if you don’t, nothing more I could say or do will help you. As for me, I’m neither a mechanic nor an engineer. I was a painter back in the ‘70s (I’ve painted every bike I’ve owned) and later became a train driver (railroad engineer if you live in Nth America) but I enjoy playing with machinery and wondering how I can make it better.
BTW, the 40t, 21mm rear pulley in the pic of me holding it fresh off the mill is now surplus to requirements and is for sale. I’m asking the cost of a new pulley from Gates and you get the machining and gold-zinc plating (as shown in pic of it next to the unmachined 90t pulley) for free. If you want it, email me davidrayner23t@gmail.com I have no idea how to insert pics here so email me and I'll send them to you. Ask questions about any of this if you like and as with the red Special and blue chopper, please send pics if you go through with it.
Last edited: