First of all credit has to go where credit is due. I did not develop this mod, all of the credit for that has to go to Dennis Vernadore, . He sells complete systems for $570, contact him for more information. Most of the information that I am providing is only for if you want to buy the parts and do the machining yourself.


This note added 07-24-02 and applies to the instructions below:

Those [these] are the instructions that I've been sending out. That pretty much
covers the alignment issue and the how-to stuff. The only things to add

1. Use the next larger sprocket size for the front.

2. Use the new Gates belt that is stronger - don't know the part number.

Cap'n Kirk

Here are the parts that are needed for the belt drive system. All can be obtained from the Gates Rubber Company. Go to this web page and find your regional Gates representative and give them a call. They’ll put you in touch with someone in your area that can sell you the parts. Gates does not sell direct. I purchased my parts from Berry Bearing for $189 total.

Front Drive Sprocket #8M-34S-21

Rear Drive Sprocket #8M-80S-21

Poly Chain GT Belt #8M-1792-21

Here’s the section of the Gates catalog that talks about the Poly Chain GT Belts:

Here’s the catalog info on the belt:

Here’s the section of the catalog that talks about the sprockets:

Here’s the catalog info on the front and rear sprockets:


All of the machining of the belt drive system can be completed with a lathe. A CNC mill or CNC lathe may be used but are overkill. You will need to work out some way to clamp the parts in the lathe’s chuck without warping or otherwise damaging the parts. I had separate jigs made for each part to hold it properly. I can rent these jigs out to anyone who wants to use them and cut down their prep time, e-mail me for details.

A special note of thanks goes to Steve Pixley and Kevin Lesard the machinists at my work who helped me immensely with this job. When I say "we", I’m talking mostly about these great guys.

Here is what will need to be done, part by part:

The Old, Stock Front Sprocket

You’ll still need to use this part in the new system. Take the rubber off of the part (this will take some cutting and prying, it’s on there pretty good). Either bolt the sprocket in a jig or hold it by the inside hole. Machine off the teeth of the sprocket and cut it down to 2.826" outside diameter. Dennis cut the sprocket down to an outside diameter of 2.750", however I didn’t feel that this left enough material on the outside of the holes that were to be used later in bolting it to the new sprocket. My dimension of 2.826" will make the finished part a little beefier because all you are doing is cutting just the teeth off. The teeth are very hard so this will be the most difficult metal to cut in this project, so make sure the sprocket is SECURE in the lathe.

New Front Sprocket

Bore out the inside to 2.828" by 0.623" deep. Dennis specified boring to an inside diameter of 2.752", but we cut the hole bigger to accommodate the bigger outside diameter that we cut the stock sprocket to (see above). If you look at the belt sprocket you can see that it is basically three pieces. There’s the main part of the sprocket with the teeth and then there are two round rings pressed onto the main sprocket that function as guides for the belt. When you bore the sprocket to 2.828" you are taking off all of the material from the main part of the sprocket that is holding on the belt guide. Guess what happens when you take this material out? At some point the belt guide on the side that you are machining will fall off! I think that’s why Dennis specified a cut to 2.752", because that would leave 0.038" of material on each side to hold the belt guide piece in place. That isn’t much though. So we figured just take the damn thing off. We then drilled and tapped four holes into the teeth of the belt sprocket and drilled matching holes in the belt guide so that it could be re-attached later. The belt guide attachment isn’t terribly robust, but it also doesn’t get a lot of force applied to it. It’s attached with small allen head bolts. Finally you’ll need to drill matching holes to the old sprocket so that you can bolt the two together. Dennis drilled holes all of the way through for " bolts. We drilled and tapped the holes for 5 mm allen head bolts. When putting everything together I used Locktite Blue on all bolts.

New Rear Sprocket

Something fairly interesting happened with this part. I took the old chain sprocket off the bike and measured the inside diameter of it to be 4.725". However, Dennis specified that the inside diameter of the belt sprocket be machined to 4.650", a 0.075" interference. Either Dennis’ measurement is a typo or there is potentially a hub difference between models (although both of our bikes are Classics). Play it safe and measure the inside diameter of your chain sprocket or measure the hub’s outside diameter at the mounting point. For the machining of the sprocket we first match drilled holes using the chain sprocket as a guide. The center to center distance between holes opposite of each other was measured to be 5.512". The center to center distance between adjacent holes was measured to be 2.756". We drilled and tapped these holes to a smaller diameter than required and used these holes to mount the sprocket to a jig. When we were all done the holes were drilled out to the required size (13/32" diameter). The inside diameter was bored to 6.780" diameter by 0.623" deep.

Here’s a quick sketch of the measurements we got for the hole placement:


image8.gif (2015 bytes)



Instead of trying to eyeball the placement of these holes you could use these measurements to start the holes in a CNC mill.

Belt Alignment

The alignment of the belt is not terribly good in my opinion when the belt sprockets are bored to the dimensions described so far (0.623"). My input along these lines is summarized in the e-mail copied below:

I had some time this weekend to get some measurements on my belt drive system and I believe that I am prepared now to speak intelligently about why there is a slight misalignment. Again, what I am referring to is a rub along the right belt guide in the front, which coincides with a rub along the left belt guide in the rear. Although I only see this as a minor problem, I wanted to get to the bottom of the cause and try to remedy it.


As I've stated before, it appeared to me through visual inspection and the use of a straight edge that the front sprocket was sticking out more from the bike than the rear sprocket, which would explain why the belt travels where it does. See the drawing below of this.


image6.gif (5812 bytes)


I felt that the front sprocket needed to be moved in more to get the alignment better. Going on rough measurements using a straight edge we bored the inside of the front sprocket from 0.623" deep to another 0.100" deep. After a test fitting on the bike and run, we tried boring another 0.050" out of the front sprocket. Currently my front sprocket is bored about 0.800" deep with about 0.438" of material left holding everything together. The alignment seems to be slightly better, but not perfect. I decided to give up on this rough guessing and to do some real measurements and calculations to get this right.


Okay, the front and rear sprockets are about the same thickness ~ 1.25", the Gates prints support this. Thanks to Charlie for supplying these prints. I'm guessing that Dennis came up with the bore depth of 0.623" by basically boring half of the 1.25" of material out. I think the assumption was that if the sprockets were bored to the same depth, then the alignment would be good. The problem is that the stock front sprocket aligns the new belt drive sprocket, whereas the stock sprocket is removed in the rear. Thus the stock front sprocket works as a spacer, moving the front belt sprocket out from alignment with the rear sprocket. It is moved out by 0.343", the thickness of the drive area of the stock front sprocket. My picture below tries to illustrate how the belt sprockets are out of align with the original path of the chain.

The key number here is 0.343" or 11/32", this is the thickness of the chain sprockets and this is the difference in the alignment of the belt drive sprockets. This is assuming that the stock sprockets were perfectly aligned, which I think is a safe assumption.

To get the two sprockets perfectly aligned one would either have to bore the front sprocket more, bore the rear sprocket less, or do a combination of the two. The rear sprocket on my bike bored to 0.623" only has a little less than 0.100" clearance to the swingarm. It's in there really tight. I think you could bore the rear sprocket less, but not by much without getting it even tighter. If I were doing it over again I would bore the rear sprocket to a depth of 0.600".

If you took it all out with the front sprocket you would have to bore it to a depth of 0.623" + 0.343" or 0.966". With my sprocket bored to 0.800" I still have about 0.155" clearance to the engine case, so there actually might be room to do this. However, the more you bore, the less material you've got holding the sprocket together. I am not comfortable going beyond the 0.800" bore I already have, taking into consideration the structural integrity of the sprocket. So the answer in the end is that you can get perfect alignment - bore the rear to 0.600" and bore the front to 0.943". However, I wouldn't cut the front sprocket down this small. In the end I think one will have to sacrifice alignment a little for structural integrity.

There realistically is some play in the system too. The gap that the belt has to run in is larger than the belt itself. The gap is 0.96" while the belt is around 0.825" (21 mm, mine actually measured 0.8125", wear maybe?). That gives about 0.068" of play on each side of the belt. So to get the belt from riding on the guide you only need to get it within 0.068" of perfect. Add to this the general slop in the system and the fact that you're working with a flexible belt and I think you can get good results from just getting as close to perfect as you're comfortable with.

I am going to recommend to others a bore depth of the front sprocket of 0.800" and a bore depth of the rear sprocket of 0.600". This will decrease the 0.343" difference by 0.200" to 0.143" which is only 0.075" away from having the belt off the belt guides. I think that over the long run just having a seventy-five thousandths misalignment as compared to having a third of an inch misalignment is going to mean less wear and tear on the belt and less stress on the belt guides (remember my front guide is bolted on and I want to reduce the force applied to it by the belt).

One other option that may be experimented with would be to remove some material from the front stock sprocket. It is 0.343" thick where it is bolted to the belt drive sprocket. If you cut some material out of the stock sprocket you're going to reduce how much it spaces the belt drive sprocket out. Cutting it from 0.343" to 0.200" along with the other changes I recommend would give perfect alignment. However, I am again reluctant to do this for the sake of maintaining the structural integrity of this part. Maybe taking the 0.075" out of the stock sprocket would be okay though. I'm not going to mess around with it, but it's a direction that someone else might consider taking.

Those are my conclusions and I believe very strongly that my measurements back them up. Please let me know if you have any further input or questions. Thank you again Dennis for coming up with this mod. I am not trying to down play the hard work that you did in any way. It works and it works great, this is only a very minor problem that I hope to minimize for others who will be doing this mod.

So, if you’ve followed what I wrote, I would not recommend the bore depths of 0.623" that Dennis has specified. I instead would recommend a bore depth of 0.800" for the front sprocket and 0.600" for the rear sprocket. Unfortunately, since this mod just hasn’t been done much, you are going to have to experiment a little to get the kind of alignment that you want.

Stock Sprocket and Chain Removal

This is not an easy job, it’s going to take several hours. First remove the side cover on the left of the bike that covers the front drive sprocket. It should be held on by one allen bolt. Don’t loose the rubber gasket wedged in there. Now bang flat the washer under the nut that holds the drive sprocket on. This washer should be bent up in one place. A hammer and screwdriver should get that bend out. Now have someone stand on the rear brake while you take the nut off (it’s a 27 mm nut). Note that the nut is on there TIGHT. I only got it off by using a large socket wrench with a 4 foot bar placed over the handle for extra leverage. Now loosen up the rear wheel and move it forward, just like you do in chain tension adjustment and you should be able to take the front sprocket off the drive shaft.

Rear sprocket removal is easy. Just take the rear wheel off and unbolt the sprocket.

To get the chain off you’re going to need to take the swingarm off of the bike. I’m not going into all of the gory detail here though. You need to get a service manual if you don’t already have one and follow the directions there, it’s very accurate and has nice pictures. As long as you have the swingarm off, why don’t you lube the rear end too, it should be done every 6,000 miles. You’ll need to have the swingarm off to put the belt on (not the sprockets, just the belt). I would recommend taking the swingarm off when you get your parts, but the belt on, lube the swingarm, rocker arm, etc., and then button it back up. Then when you’re done modifying the sprockets you just need to bolt them on and go!

Hey big revelation here…’s a pain in the rear to get the belt on isn’t it? I mean you’ve really got to rip into the bike to get the belt on. Well keep that in mind because if your belt ever breaks you’re not going to be able to just fix it on the side of the road. It’s a four hour job and you need to jack the whole rear of the bike up off the ground to do it. I would highly recommend buying an extra belt and taking it with you if you ever go on an extended tour. That way if you break a belt you’re only going to be down for a few hours while you take the bike to a garage for the repair. If you don’t have an extra belt on hand, then not only will your bike be un-repairable on the side of the road, but it will also be un-repairable for a couple days until you can get a new belt shipped to you. So if you’re too far away to get the bike back home easily, get yourself an extra belt to carry along. An alternative would be to carry an extra chain and chain sprockets so that you could switch back to the chain system if needed. This would only be an advantage if you used a chain with a master link on it, that would alleviate the need to remove the swingarm.

Belt Drive Install

Installation should be a breeze now, because you should already have the belt on and the rear tire off. Just bolt on the new rear sprocket. I’m not sure about the proper torque settings. I just got it really tight. These bolts are readily accessible and should be checked for looseness after a couple hundred miles. The front sprocket is bolted back on with the locking washer and big 27 mm nut. Put a little engine oil on the drive shaft before installing. Get the front sprocket on, the washer, and the nut. Then get the rear wheel on and tightened up. You’ll want the belt tight on the front sprocket before you tighten down it’s retaining nut. Okay, now have someone stand on that rear brake again and put 92 ft lbs of torque on the front sprocket’s 27 mm nut. Now bend up one corner of the washer, bolt the cover back on, and you should be just about good to go. Make sure the belt is TIGHT. I have my rear axle set between 4.25 and 4.5 notches back on the swingarm. If you skip teeth on the belt, then it’s not tight enough. It’s got to be TIGHT.

Here’s what I’ve written about my impressions of this mod so far:

The belt - I've seen the belts on the Polaris, Harley, and Road Star, and they're all much beefier than this belt. The belt for this mod is not nearly as wide as those other belts. However, there is not room between the frame and the swingarm for it to be any bigger. The belt does appear to be constructed from the same materials as those used in these other machines. It is made by Gates that makes the belts for Harley (and probably Polaris too). A Vulcan riding friend of mine works with Gates Poly GT Chain belts in manufacturing applications and he swears that this belt is as tough as they get and should be more than capable of taking the forces applied by the 800.

The sprockets - The sprockets are solid, there's no concern at all about these babies holding up over time once you get your hands on one.

Machining - Although the instructions were helpful, there was still a lot we had to figure out for ourselves. All of the machining can be done on a lathe. You could also use a CNC mill or CNC lathe, but that would be overkill. The hardest part was figuring out how to fixture the parts in the lathe and then making jigs to hold them. I took pictures along the way and will be working on developing an extensive and clear set of instructions on how to do the machining, including drawings and photos.

The fit - The rear sprocket fits PERFECTLY on the hub. Everyone who's seen it has commented that it looks like a factory option. It looks like a very professional install when completed.

The ride - Okay, here's the really important part. I've only put on about 1,000 miles with this mod, but I do have some impressions. First of all don't worry about the belt not being strong enough, she's plenty tough. My 800 is hypercharged and tuned for good power with Vance and Hines Straightshots. You're going to find others with the same setup and the same power, but I don't think you're gonna find another 800 with more horsepower or torque than what you would see with this setup. Now I've put this belt through the roughest torture tests I could imagine - 400 miles at 73 mph interstate travel, acceleration from 0 to 60 in only 1st and 2nd, roll on up to 90 mph. Through all of this testing the belt drive hasn't flinched even once. Now I did have some problems initially with the belt slipping with lots of torque, but I had it too loose. You have to take ALL of the slack out of a Poly GT Chain belt. Once I got the belt tight on there it didn't slip, ever. Now I'm not saying that the belt drive performs any better than the chain. The power delivery and performance doesn't feel any better or worse than the chain to me. I do notice the change in the gearing though, and it's for the better. I used to have to shift from fourth into fifth at 50 mph. But now I don't shift until 55 mph and the engine is at much lower revs at normal highway cruising speed. Interstate pounding at 70+ mph still has the engine up into some high revs, but around town and country cruising is much more relaxed.

Those are my impressions. I think it's a pretty great mod. I killed my chain after 18,000 miles and needed to replace the chain and sprockets. Well for about the same amount of money I got all of the parts for the belt drive conversion. Now I really benefited by getting the machining done at my work, but I doubt if many of you will be that lucky. In the long run you should never have to buy any more sprockets and maybe only one more belt ($40) within the life of your bike. So, if you're looking to ride your machine for several years and try to squeeze 100,000 miles or more out of it (I am), then the belt drive certainly makes some payback sense over time. Plus you'll only have to adjust it a couple times and then forget it, no lubing, no mess, no constant adjusting of slack.

That’s it, e-mail me if these instructions need to be changed or updated. I can also send jpeg pictures of the Gates prints for the sprockets.

Good luck,
Cap’n Kirk
VROC #928
VRA #1-10-3A-800B1
’96 800 Classic
Bloomington, IN


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