Clutching questions and/or theories

[Mjunkie]

I recently finished putting my cpc 1300 motor together in my M7 141 chassis. I kept the M7 diamond drive and 10" secondary, but put in a higher gear ratio in (don't remember exactly what it is right now) thinking that with that motor and that short of a track, I'll have plenty of torque for the higher gears. Dale has clutching recommendations for the 1300, but of course in my situation there are so many differences his recommendations can't be very reliable, but I thought I would start close to his recommendations and go from there. I have a P85 conversion in for the primary, and have cutler's torsional conversion on the M7 secondary. I bought an orange secondary spring for the secondary (his recommendation to start at) and have a straight 44 helix. His helix recommendation is a 42/38, but I thought I'd just start with the straight 44 since I already had it and figured it would give me a starting point to go from just as good as the 42/38. Anyways, the orange spring is EXTREMELY stiff. It's stiffer than any other secondary spring I've ever used before. It took two people to put the clutch together and to put the belt on, there was NO way to simply force open the sheaves to fit the belt in without screwing in the belt deflection adjuster WAY in to open the sheaves. I haven't had a chance to run it yet, but it got me thinking that with that stiff of a spring I will have to run LOTS of weight to clamp the belt hard enough to force the secondary to upshift. In my mind I think that with that much weight clamping down on the belt, I probably won't get very much or any at all belt slippage at the primary. If there's little or no belt slippage at the primary, all of the power the motor is creating is getting transfered to the secondary. So when I hear about some people going to lighter weights and a steeper angle of helix, is that not as efficient as the other way around? It makes sense in my head that if you minimize the slippage at the primary, all of the power is getting transfered to the secondary and that if you have a stiff enough spring in the secondary to reduce slippage there with the correct angle of helix to keep the rpm where it needs to be, that power will then be transfered to the track. Am I out in left field or does that even make sense what I'm thinking? Another way of saying what I'm saying is that clutch tuning should be doing what you need to, to eliminate belt slippage as much as possible in both the primary and secondary so that all of the power created by the motor is transfered to the track. Does that make sense?

 

[prox660]

without overthinking this.....don't confuse static weight with upshift force. a lighter weight allows your motor to move up 200-300 rpm and develope more shift force as force varies with the square of velocity (rpm). The spring from cutler is able to produce enough side force to prevnt slippage.....of both the primary and secondary, not just the secondary, and it will also help your backshift The only torque sensing component is the helix......think of it as a wedge....shallower angle creates more side force, greater angle creates less sideforce....as a function of torque resistance.

 

[Mjunkie]

I think I understand at least part of what you're talking about. I understand what you said about how rpm effects clamping force on the belt. You said that a lighter weight will allow more rpm and that higher rpm will increase clamping force on the belt more than a heavier weight at a lower rpm (at least that's what I understood from your first statement). I can see that and understand that. My point is that with such a stiff secondary spring, I will have to run heavier weights (than I had before thought I would) because of how much force it will take from the primary to force open the sheaves of the secondary to upshift (because the spring is SO much tighter than I anticipated starting with). So I need to re-think my initial set up. If I run the weights I thought I would need in the primary, I will probably over-rev, which means I'll have to run heavier weights than I first thought.

About the helix, are you saying a shallower helix will have more clamping force than a steeper helix because a shallower helix requires more twisting to open the sheaves all the way (and thus more spring to overcome) vs. a steeper helix that has much less twisting of the spring?

I'm obviously no expert at clutching, but think I understand the basics. The spring from Cutler was just SO much stiffer than I had ever used before that it got me thinking about a different theory on the best way to clutch. Obviously a stiffer spring will take much more force to overcome and in turn clamp on the sides of the belt more than a softer one (want to hold it into a lower gear in other words and so more backshift also). I understand the helix is the torque sensing part of it, but the helix and the spring work in unison to a degree as far as clamping force. I don't understand how the secondary spring will add clamping force to the primary though, other than maybe because the secondary will require more force to open which in turn will hold the belt lower in the primary until the sufficient force is met to open the secondary and allow the belt in the primary to move up the sheaves.

 

[prox660]

I wouldn't wory about wts vs secondary spring......Cutler will know from experience that his helix and spring will generate enough sideforce to hold onto the belt with your 1300....thats a given. All you have to do is find the weight and primary spring combo that allows your motor to respond off the bottom and peg the tach at rated rpm.....start light on the weights.....fine-tune with the primary spring.

 

[DLynn]

Prox has some good advise. Always default to a proven / tested setup and then adjust from there. Make a list of what is going to happen if you change the primary weights, primary spring, secondary spring, or change the helix.
Good Luck

 

[go high fast]

grab the Clutch Tuning Handbook by Olav Aaen. Best investment of time and money I ever made. Then grab his Carb Tuning Handbook and you are on your way to a lifetime of enjoyable sledding.

 

[DLynn]

I agree...The Olav Aaen's clutch tuning hand book is a great resource. It's really crazy is that as old as the book is the theory still applies. It's time for one of the big boys to come up with a new drive system.

 

[Mjunkie]

Prox has some good advise. Always default to a proven / tested setup and then adjust from there. Make a list of what is going to happen if you change the primary weights, primary spring, secondary spring, or change the helix.
Good Luck

That's just it, with the variables I have, there is no ”default proven tested setup”. My gearing is different than what Dale tested with, my track length is shorter than any he tested, and my primary is a polaris, which he also never used. I'll use his setup as a starting point on the secondary, knowing it will only be a starting point, and I'll take a good stab in the dark on the primary.

The suggestion on the clutching book is a good one. Thanks, I'm going to pick one up.

 

[volcano buster]

Do you have a rough idea on the Hp/Torque numbers of your motor and at what rpm? Is this more of a torque motor that revs a little slower, or is it one that revs real fast?

 

[Mjunkie]

Do you have a rough idea on the Hp/Torque numbers of your motor and at what rpm? Is this more of a torque motor that revs a little slower, or is it one that revs real fast?

I don't have good hp and torque numbers. He says the motor will produce up to 225hp but I'm sure that is with a straight race gas head at sea level. I've never heard a torque spec, but it has to be a torque monster. I ride at around 6k to 10k in elevation and I'm running the pump gas head. I think it's a slower revving, higher torque motor, but I'll find out when the snow comes again. I think I know enough about clutching to get it figured out. I just don't have a very good idea of where to start.

 

[Mjunkie]

Almost forgot, target rpm is 7700.

 

[Griff]

As ProX660 said, you are complicating your path to a good set up by involving the primary weights with your secondary set up. You have changed enough on your whole sled that you are likely looking at a couple test and tune sessions. I'll add to the recommendation on Aaen's book. That'll be a good summer study project. Then you might want to get another secondary so you can take two set-ups for your test and tune sessions. It will pay for itself in time savings. If you get another secondary be sure to set the alignment and record it so you can swap secondary's on the snow and still achieve proper alignment. Good luck.

 

[Polarisrocks]

I think you are over thinking it... I would stick with the shallow helix a and add lots of weight till it wont pull the weight anymore.. When we built our 1200 wc sled motors we tried it all and ended up back really close to stock clutching with heavy weights.. You have to remember the steeper the helix the faster the torque will force the secondary clutch open. So if your drag racing, yes steep.. but if your tree riding or boondocking, you want a shallower helix.. Also remember you have a roller secondary and it move or shifts fast!! too fast if it too steep making lots of heat slipping.. If it were me I would put that m8 helix in there, 38* and cutler orange spring with some heavy weights and give it a whirl.. Also remember the torqional setups use less weight than the stock compression type..
The 10 series weights for the p-85 are cheap.. don't spend a bunch of money on adjustables.. Get some used ones from the Polaris dealers(take outs) and start around 10-72's

 

[volcano buster]

I'm running 10-62's in the primary. I think I can pull a hair more weight. What are the opinions on picking up some 10-64's and taking weight off the tip to make some 10-63's? Keeps the profile of the 10 series, but keeps the weight in the heel? I have a digital balance so I should be able to keep them pretty close to even amongst the 3.

 

[DLynn]

If you look at the 10 series weight, it was developed for the Polaris triples in 1823 +/-. This is why we see most aftermarket weights that have gone heel heavy style. Your concept of making a 64 into a 63 weight will work. Once you get close and it appears to do what you are trying to accomplish then you can spend 150 to 200 and get a modern weight design.
Just my 2 cents. However we do this all the time. A bench grinder and a gram scale.