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Smaller primary rollers

Studroes144

Studroes144

TY 4 Stroke God
Joined
Oct 30, 2013
Messages
2,897
Location
Lowville, NY Tug hill snowmobiling
curious is anyone with a stock or n/a viper has used smaller rollers in the primary? Seems I remember reading years back how a lot of nytro guys liked that approach. I run apex 14.5mm rollers on my turbo, engagement is noticeably lower and rpm's seemed to hold very consistent and never have any belt slip. I believe thunder products has 14.8mm rollers? Just thinking about all the different steps that guys take to adjust clutching to their liking (different primary springs, weights, belts, shims etc. etc.) and the smaller rollers seem like something that's maybe getting overlooked. They'll lower engagement and have more belt force, should in turn have a slightly better chance of keeping the machines off the stock rev limiter. Seems like everyone complains of too high engagement, belt dust from the stock 8jp belt (personally I got more belt dust from the 8dn that I did the 8jp), hitting the rev limiter easily and lack of top speed. Thoughts or feedback?
 

Never tried myself. Always thought about the gap between rollers and wieght at rest also. Seems large compared to a cat clutch. I am sure once running even at idle that gap is closed and spring comes into play but smaller roller would contact wieght at point further down wieght. Cause of bigger gap.
 
I could be wrong, but in my past experience with 2 smokes aka piped vipers. I was always taking the factory 14.5 mm roller out and installing 15.6 mm ones in. Reason being is that when installing the heel clicker weights, they were so aggressive that it was very hard to keep traction. One way to help with this issue was to swap put the rollers to smooth out the "hit" on bottom end.

My opinion,. I think swapping to a smaller roller would increase the force of the weight, but you would also have to make sure you have the traction for it as well.

I may have it backward as it's been a year or so since I been in my notes
 
I'm still a rookie at clutching but I thought bigger roller's lower engagement, as there is less space between the weight and the roller, correct me if I'm wrong.
 
murdered137 said:
I'm still a rookie at clutching but I thought bigger roller's lower engagement, as there is less space between the weight and the roller, correct me if I'm wrong.
Click to expand...

Smaller rollers actually lower engagement, think of the gap between the weight and the roller, smaller roller = more gap. When the engine is running the weight is flung out to contact the roller and then all that's left is to overcome spring tension to start engagement. Since the roller is smaller it gives the weight a chance to fling out more and in turn it puts it at a point further in its shift curve and has more centrifugal force that a weight that is being held further back in its shift curve. The roller itself isn't doing anything, it's all about the weight being flung out more or less depending on roller size and the more or less centrifugal force that's present because of it. To the comment of the bigger roller in the older 2 strokes I can understand that being probably a short track sled and realistically a suspension that wasn't setup good for great traction to begin with. With the procross chassis there's a much greater chance of good traction just in the chassis itself. Wish more guys had vipers around me now, they've all moved on to sidewinders. I'd love to see a bone stock sled with smaller rollers and maybe a spring swap to get revs right.
 
Studroes144 said:
Smaller rollers actually lower engagement, think of the gap between the weight and the roller, smaller roller = more gap. When the engine is running the weight is flung out to contact the roller and then all that's left is to overcome spring tension to start engagement. Since the roller is smaller it gives the weight a chance to fling out more and in turn it puts it at a point further in its shift curve and has more centrifugal force that a weight that is being held further back in its shift curve. The roller itself isn't doing anything, it's all about the weight being flung out more or less depending on roller size and the more or less centrifugal force that's present because of it. To the comment of the bigger roller in the older 2 strokes I can understand that being probably a short track sled and realistically a suspension that wasn't setup good for great traction to begin with. With the procross chassis there's a much greater chance of good traction just in the chassis itself. Wish more guys had vipers around me now, they've all moved on to sidewinders. I'd love to see a bone stock sled with smaller rollers and maybe a spring swap to get revs right.
Click to expand...
I might be wrong but I believe the adjustable 911 cover I have also changes that gap as you adjust for the belt width. Ideally there would be no gap so you can take advantage of entire wieght profile which can really be fine tuned.
 
cannondale27 said:
I might be wrong but I believe the adjustable 911 cover I have also changes that gap as you adjust for the belt width. Ideally there would be no gap so you can take advantage of entire wieght profile which can really be fine tuned.
Click to expand...

I'd say that's true as long as there's enough belt grip, on my 800 I run I fairly wide belt so tolerances were a bit tighter and had to shim the primary because I was getting a lot of belt slip off the line..was leaving solid black rubber marks on the primary from slipping. Now with the shimming done it engaged lower and grabbed the belt hard so I'm running a really stiff spring and engaging at 4200 and it's a rocket off the line and holds steady consistent rpm the whole way with a fixed non adjustable Arctic cat weight. The outcome of the shimming is doing the same thing as just swapping out to smaller rollers, more space between the weight and the rollers so when the weight is flung out it has extra force pushing on the belt.
 
I have probably 7 or 8 sets of 14.5 mm rollers, I'll give it a try with my magnaforce weights, what's it going to hurt. I can only see a good out come out of it because I also see and issue with the initial engagement of the belt force on the viper. Time will tell, we need snow!
 
yammitrip1 said:
I have probably 7 or 8 sets of 14.5 mm rollers, I'll give it a try with my magnaforce weights, what's it going to hurt. I can only see a good out come out of it because I also see and issue with the initial engagement of the belt force on the viper. Time will tell, we need snow!
Click to expand...

I'd be real interested to hear what your outcome is, I have no idea, never tried it on an n/a sled..but it seems like all the characteristics of a smaller rollers are things that would benefit the viper.
 
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