Clutching ideas

Backwoods M Max

Backwoods M Max

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Mar 31, 2011
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New England
I need to work on the clutching for the mountain max this fall. By sharpie I'm only getting half way up the primary. Clutching is www primary spring, stock weights/rivets for 0-3500'. Secondary has a silver spring at 60 wrap on stock helix. Gearing is dropped to 20/39. Belt is a new broken in ultimax xs-805. Sheaves are clean. Up shift is around 8500. Max rpm is around 9500. I want more track speed. Is putting the 17.2mm rivet in both holes a good starting point for more weight, or should I look into other arm profiles? Being at sea level that's the heaviest I can go before I need to start with a heavier weight arm.
 
sounds like your over revving. Your silver spring might be to tough. Also make sure your clutches move freely with no binding. With the primary spring out your halves should drop with no resistance. Also how old are your springs. Might be warn out.
 
The springs were brand new last year. They were tom Hartman's recomendation for the sled. The clutches were good when I put the springs in. No binding and the rollers/weights didn't have any slop. The primary spring dropped my engagement down 600 rpm which is what we wanted, and the secondary spring was suppose to keep it from back shifting too late and bogging the engine when you start to really dig in.
 
well, first off what spring was in the front before you used the w/w/w yamaha???, because you say the www dropped the engagement speed but its only a 45kg start.
secondly, the silver sec spring is way too stiff and more then likely why you cant get the belt up past half shift because the rear spring is trying to backshift the clutch and the soft front spring(45/119kg) requires less weight in the arms = less force and cant overpower it and upshift, so you have a case of the rear clutch fighting the front clutch.
 
A green spring came out of the secondary, it was at 70 wrap. The primary had the ywy in it. both springs were stock by the book.

As far as weights, looking at the weight chart if I can't get enough weight in with the 2 biggest rivets, would I just go up to a weight that's in the low 40's for base weight since the 8CR can only get so heavy with 2 4.5g rivets in it?

should I have gone the other way in secondary weight, softer than stock down to a red?

tom hartman seemed pretty adamant about spring weight and said it could be dialed with rivet tuning from there. he does deal with these sleds at 10,000ft not sea level.

Not sure how it plays into it, but the manual for the MM700 at sea level specs a 23/40 gearing, which is 1.739:1 with a 13.9 and 17.2 rivet. At 1.95:1 is it possible I just can't put big enough rivets into the 8CR weight for it to work right with that much torque load reduction on the engine? At that point, would a heavier starting weight be the next step?
 
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I wanna avoid getting into the middle of the tom hartman said this is what to use, obviously it doesnt work correctly so lets just look at how to reduce the rpm and avoid the he said this and that.
Just looking at your post and reading them you said the engagement dropped 600rpm, well... it cant, because both primary springs have the same exact start rate, which is 45kg, the yellow white yellow is 45/128, the w/w/w is 45/119kg, so if we remove everything else from the equation the engagement speed stays exactly the same... the shift out rpm will be slightly lower because the w/w/w spring is softer and that makes the untouched primary weights heavier,which lowers rpm on the shift out only. The differance between those 2 springs is pretty small.

Now, you added a stiffer rear silver secondary spring which will do 2 things, it will resist the upshift of the front clutch,and it will also want to backshift sooner due to the increase in spring torsional rate. What happens is the rear clutch fights the front clutch,and you get a dead zone where the sled doesnt gain mph or rpm but just makes noise,because the rear is fighting the front.

gearing, whenever you go to a numerically higher ratio(lower gearing) you decrease the load on the engine/clutchs, it will multiply the torque from the engine and it allows the same clutch set up to run higher rpm because of the loss of load. So you would automaticly need to do 1 of the 2 things, you would add rivet weight or go to a lower shift rate spring(which is what you did in your case)

what you should try first, is to put back in your stock green dot sec spring and add rivet weight to the tips of the current clutch arms along with keeping in the w/w/w spring. If you have the stock pipe on you want to stay around 83-8500rpm, over that and your just wasting power by far. See where your rpm is and then report back, it can be tuned in with relative ease if you can relay the information the tach gives your eyes. .Having the low gearingand the stiff rear sec spring rate is what is the bulk of your high rpm problems, you can also add washers to the rivets to make the weights heavier if needed. i even use 1/4"-28 bolts and nuts in them to tune them into your paticular combo. Just telling you theres options out there to make your current weights heavier if needed.
 
mrviper700 said:
I wanna avoid getting into the middle of the tom hartman said this is what to use, obviously it doesnt work correctly so lets just look at how to reduce the rpm and avoid the he said this and that.
Just looking at your post and reading them you said the engagement dropped 600rpm, well... it cant, because both primary springs have the same exact start rate, which is 45kg, the yellow white yellow is 45/128, the w/w/w is 45/119kg, so if we remove everything else from the equation the engagement speed stays exactly the same... the shift out rpm will be slightly lower because the w/w/w spring is softer and that makes the untouched primary weights heavier,which lowers rpm on the shift out only. The differance between those 2 springs is pretty small.

Now, you added a stiffer rear silver secondary spring which will do 2 things, it will resist the upshift of the front clutch,and it will also want to backshift sooner due to the increase in spring torsional rate. What happens is the rear clutch fights the front clutch,and you get a dead zone where the sled doesnt gain mph or rpm but just makes noise,because the rear is fighting the front.

gearing, whenever you go to a numerically higher ratio(lower gearing) you decrease the load on the engine/clutchs, it will multiply the torque from the engine and it allows the same clutch set up to run higher rpm because of the loss of load. So you would automaticly need to do 1 of the 2 things, you would add rivet weight or go to a lower shift rate spring(which is what you did in your case)

what you should try first, is to put back in your stock green dot sec spring and add rivet weight to the tips of the current clutch arms along with keeping in the w/w/w spring. If you have the stock pipe on you want to stay around 83-8500rpm, over that and your just wasting power by far. See where your rpm is and then report back, it can be tuned in with relative ease if you can relay the information the tach gives your eyes. .Having the low gearingand the stiff rear sec spring rate is what is the bulk of your high rpm problems, you can also add washers to the rivets to make the weights heavier if needed. i even use 1/4"-28 bolts and nuts in them to tune them into your paticular combo. Just telling you theres options out there to make your current weights heavier if needed.
Click to expand...

Thanks for the feedback. I have 6 17.2mm rivets on the way and the original green secondary spring sitting around. I will put the green back in when we finally get snow again and see how that rides on the heavier weights and softer secondary spring.

Can you educate me between spring wrap in the secondary? Tom had told me to run the 60* wrap here at sea level, then when I finally get out west on a planned trip to load the spring to 70* wrap and it should make up for the power loss at the high altitude.

As far as tuning down here at sea level with the green spring back on, how does changing wrap effect the shift? what does going from the book 70* to 60* do to things?


Thanks!
 
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