How to? belt for mod

[99summitx]

Ok we are just finishing up a mod sled, we put a 995 tripple running 100% race fuel with nos into a 99 summitx s-chassis, 156'track, primary clutch is a polaris p-85 with a TRA secondary. Question is how do you figure what belt to use, what measurments are needed to fit belt and then is there a chart to match up belt to measurements. The 670 belt is to long and narrow so clutch engagement is around 5500-6000rpm. Any advice would be helpful. Thanks in advance

 

[CrankShop910]

Most of the time you chose your belt centers before you mount the motor,
IE 10 3/4, 11 1/2, 12"... Look at stock sled and find the belt center that will work for you, then you will have the right belt size for your app..

 

[rsaint]

Is the 995 a rotax bottom end and using skidoo mounts from a 97 809. if they are the belt should work i had a 809 p85 and cat secondary in a s body worked very well. You may have to re shim your p85 take shims out to match the width of the belt. What is the center to center from crank to jackshaft also you should have a .62" between the clutches.

 

[ForeverRMK!]

Your RPM'S for belt engagement is adjusted with different springs on the Polaris primary clutches,that could be your fix.

 

[99summitx]

Is the 995 a rotax bottom end and using skidoo mounts from a 97 809. if they are the belt should work i had a 809 p85 and cat secondary in a s body worked very well. You may have to re shim your p85 take shims out to match the width of the belt. What is the center to center from crank to jackshaft also you should have a .62" between the clutches.

It's a Rotax 780 bottom end, 670 rods, spacer between head and jugs, 809 head, 600 piston's built by Mott's and it's sitting on a 670 engine mount that's been modified and a extra plate added. crankshop triple pipes. Will measure cen to cen. Thanks.

 

[local legend]

measure the sheave angles. I know cat and poo are the same, but I think doo is different. you might have a tough time getting belt bite.

 

[rsaint]

It's a Rotax 780 bottom end, 670 rods, spacer between head and jugs, 809 head, 600 piston's built by Mott's and it's sitting on a 670 engine mount that's been modified and a extra plate added. crankshop triple pipes. Will measure cen to cen. Thanks.

With that bottom end you can use motor mounts from a 97 809 from a s body and you get your proper spacing for a 670 belt and i have a spare set of those mounts and they are rare. Tom is building me a 889 but i think it is going in a zx . I agree it maybe as simple as the spring in the primary.

 

[Modman]

Ok we are just finishing up a mod sled, we put a 995 tripple running 100% race fuel with nos into a 99 summitx s-chassis, 156'track, primary clutch is a polaris p-85 with a TRA secondary. Question is how do you figure what belt to use, what measurments are needed to fit belt and then is there a chart to match up belt to measurements. The 670 belt is to long and narrow so clutch engagement is around 5500-6000rpm. Any advice would be helpful. Thanks in advance

Did you get this figured?

Easiest way is to find the clutch alignment specs from the original motor that was in the chassis and find the distance between the clutches at the closest point (ski doo usually calls it the "Z" or "Y"? measurement in the manual). Now measure it with the new motor and determine the difference (shorter or longer). To get the correct belt for the new c to c, you need to know what belt it originally used (easy, just look it up at the Royal link below) then find the outer circumference for that sled belt from the Dayco or Carlisle links below.

Now take and multiply the new difference (new "Z" measurement) between the clutches by two (the belt has to travel this distance twice - once on top and once on bottom of the clutches) and add or subtract this distance from the old outer circumference. This will be your new outer circumference. Match that to a belt in the links below and find a width that is close and that will be your new belt.
Example (just using random measurements):
Old "Z" measurement: 25mm (1")
New "Z" measurement: 19mm (3/4")
Difference = 6mm or 1/4" less (so need to subtract, if new "Z" was longer then we would add it to the old belt OC below). Don't forget this # needs to multplied by 2 so the new belt needs to be 1/2" shorter.

Old belt O.C. - 45" 11/64
New belt O.C. = 45" 11/64 - (1/4" x 2) = 45" 43/64
So you could go with a Carlisle XS811 which would be a hair shorter than the ideal length and might squeal if it was too tight. So you could run it just a little farther down in the secondary to gain a small amount of length back until it stops squealing (probably wouldn't need to but you could and I don't think you would need to drop it much, maybe 1/16"??? for example). This would keep the 1"7/16 width though. Or you could run a 138-4532U3 which is slightly skinnier than the XS811. Dayco might have one that fits perfect, didn't correlate this to their catalogue, just the Carlisle one but I hope that you get the idea.
(see link here - ) with all the belt specs showing O.C. measurements and width.

Dayco catalogue (Dimensional Data starts on page 119 - http://www.daycoproducts.com/daycoweb.nsf/DaycoATVSnowmobile.pdf).

Find the one that fits or that is the closest on the width and figure out what sled it fits via the Royal Dist page here - ,

You can order any belt you want for that particular sled (in case you prefer Dayco over Carlisle, just order the Dayco one). If you know the outer circumference (O.C.) via string method from the sled, you can find the one that fits in the catalogues. Did this for my mod, ended up running belts for an RT1000. Mine fits almost perfect but you might have to make a bit of compromise on the width or the length, but usually someone has one that is close.