My thoughts on 108 Comet clutches for Vmax 540's.

[Phil Peterson (opsled)]

I've been reading some of the troubles guys are having with your engines and clutching for the 108 Comet. I think a lot of the problems you are having with the 108 is that it is a larger diameter clutch than the 102 they came with. The stock 102 primary and Yamaha secondary on the Vmax 540 are matched to work together in that the drive belt has the same distance to move up in the primary as it does to move down in the secondary. When you put the larger diameter 108 on your belt has bottomed in the secondary before it has reached the top of the primary. When that happens your primary is still trying to close but the secondary is fully open and the drive belt isn't long enough to allow the primary to open any further. At that point your engine is now trying to pull your sled and stretch the drive belt which is going to rob some serious horsepower. If you try to adjust the the shive distance or get a longer belt to compensate for this problem your belt will be so loose at the start that it won't go off the line.
A 108 is about 1/2 in larger diameter than a 102 and if you compare an Arctic cat secondary (that was paired with a 108 from the factory) you will see that it is about 1/2 in larger in diameter than the stock Vmax 540 secondary that was paired with the 102.
I have 4 108's laying here that all came off 540 Vmax's and everyone of them has a black burn mark about 1/2 in down from the top. I also have three 102's and none of them have this problem.
If you are going to run a 108 you have to have a secondary designed to work with it. You may be able to remove enough material from the backside of the stock secondary helix to allow it to open far to compensate for the difference in diameters but you will have to experiment.
Draw a line with a black marker from bottom to top on your primary and run it on a stand. If it fully shifts out the belt will remove that line. If not you have a problem that will never allow your sled to reach it's pontential.
Bad clutching can destroy the performance of a perfectly tuned engine. Don't assume that your engine is not right unless you know your clutching is. I have seen alot of people spend tons of money trying to get more hp out of an engine when all they need is the right clutching. Two guys pulling on the same end of a rope can accomplish alot. To guys pulling on opposite ends of the same rope will accomplish nothing. The same applies with your sled. If your parts are right and working together it wiil go if not it won't. When in doubt go back to factory settings with factory parts and work from there untill you can isolate your problems.
We installed a mildly ported 540 into a freind of mines somewhat ratty looking, mechanically perfect 78 SRX with Polaris primary and stock 78 secondary and once we got the clutching worked out he now has a real giant killer. He's blown away 700 SRX's, 800 Revs, Thundercats ect. His last victim has a youg kid on an 06 F-7 down the river that had a big head start. The look on that kids face was pricless when he realized he just got ran down, passed and blown away by a 50 year old (dude as he call it) riding a sled that was 10 years older than him. You don't always need alot of money to go fast.
Good Luck, Phil

[Donnie]

I partially agree with you Phil. I have a 108C on my Vmax and the belt does not come up to the edge of the flange as you said. However, mine still has the two washers installed so that I can run the stock 1 1/4" belt ( Dayco TopMax 1080 ). My clutch does bottom out and leave that extra 1/2" of space at the top, but my secondary is fully open too. The 108C was designed to run a wide belt ( 1 3/8" I believe ). To do this you would take the washers out from behind the spider. Then you could run the Arctic Overdrive. The 102 and 108 will proved the same drive ratio in a Vmax if you use the stock belt and the stock seconday.

Here's where the main problem develops. Since the 108 has that extra bit of metal on the edges, the rotational mass is different than that of the 102. For some reason, Comet thought that the stock A-3 weights and a Silver spring would be the same as the original 102 setup. Welll, they were wrong. Someone at Comet didn't pay attention in their basic physics class, which I teach at my high school. With that setup, my Vmax would engage at about 3200 rpm, dogging it out badly. I would start to get shift outs around 5500 rpm, which meant that I had no middle range at all for corners. I switched out the spring to a Red / Blue and now get about 3600 rpm engagement and shift outs near 6000 rpm. This is a bit better for trail riding, but not great. I do have a silver / orange spring that engages at 4700 rpm which is nice if you want to create a pile of snow behind you and it shifts out way too late, perfect for the lake, but not a trail unless you want to go 60 miles per hour on the trail all the time. On a stock Vmax, with a 108, I think lights weights with the same profile as the A-3 are needed. Just enough to compensate for that extra mass from the thicker face on the 108.

My brother's '86 Vmax has the orginal 102, original spring and weights. Engages about 3900, holds onto the shift untill about 6500 rpm and is just so so so smooth. I would love to find a 102 an put it back on my sled, but I can't pay what they are going for becuase the snow around here has been garbage. I haven't been on a trail ride all year. The cost doesn't match the benefits right now. So for now, I will run the 108.

I saw that someone posted a setup using a Polaris Dark Blue spring I think with the original weights. I also found some data at a Comet retailer that suggested A-1 weights with a Red spring. Trial and error, then pass it on to the rest of us.

Keep it going straight. Vmax's don't turn !!!

Donnie

[Phil Peterson (opsled)]

Hi Don, I agree that rotational mass is important and racers do everything possible to reduce it. They will use light weight speed tracks, aluminum gears, wheels and drivers, studs, titanium shafts and anything else they can think of to reduce not only weight but more importantly rotating weight. A sled with ten pounds of rotating weight removed will be faster than the same sled with ten pounds of stationary weight removed. However the differance in weight on my digital scale between a 102C and a 108C is 3.2 ounces and if you concider that adding studs to a track can add up to 15lbs of rotating mass to a sled I find it hard to believe that 3.2 ounces of clutch weight is going to cause that much of a problem. I still think that unless you can get a 108 to fully close without having to stretch the belt to do so you will never get it to work as well as a 102. You can put in different weights and or springs that will not squeeze the primary down on the belt as hard at full shiftout and gain some of your HP back but it will still be robbing HP. We ran into the same issue with my friends 78 SRX with the 540 engine, Polaris primary and stock 78 secondary. We got a combination working that would rip your arms off and pull like hell up to about 80mph and 8000 rpm where it would just seem to lay down and slowly gain speed from there. We tryed gearing, jetting, springs, weights and pipes. Every time we changed something we could change the way it performed everywhere but the top end when it was shifted out. We finally noticed a slight burn mark on the top of the primary so we cleaned it drew a line on it with a marker and tryed it again. The belt would not clean off the line at the top of the primary no matter what we did. We then removed both the primary and secondary spring, put the belt on and with the spark plugs out manually rotated the clutches and could see that the secondary was fully open before the primary was fully closed. The problem was found but how to fix it? After studying the secondary we decided to machine some material off the back of the helix where the snap ring is which would allow it to open further so the belt could go deeper into the clutch. We ended up taking out about 3/16in of material to get it right. Now the spring/weight setup is back where we started but it no longer lays down it keeps pulling right to 9500+ and with the belt now making it to the top for a higher final ratio and the increased rpm this thing is wild. We got it all dialed in just before Christmas when we had good ice but since then our ice has melted and all of the radar runs and drags around here have been cancelled. This experiance has convinced me that before you spend a bunch of time changing weights, springs and gears clean your clutch faces and draw a line from top to bottom on both the primary and secondary and try it. If the belt doesn't remove the line in both clutches you have a problem you will never fix with springs and weights. A good test if you are having troubles with performance at full shift is to put a worn (thinner) belt on an try it again. You will lose your of the line performance but if you gain on the top end its because that thinner belt has moved further down the secondary an made it to the top of the primary. Normally a worn belt will have a negitive effect on performance at any speed.
Good Luck, Phil

[Dennis]

I am also running a new 108 on my 83 vmax. I started with the stock weights and spring and had issues with large bog on the low end and only getting about 7650 for top end rpm. Changed to a dark blue polaris drive spring, it made a huge difference.
Engagement has gone up from about 3500 to around 4200, topped out I am running 8100 to 8200. Much better perfomance. Running 390?? mains I think, needles in the center, and air screws just over 1/2 turn out. I still have a slight bog on the low end, it seems to be loading up but am not sure. Any ideas on the low end will help.

Thanks,

Dennis

[vmax-540]

I think the problem that everyone is having with the 108s is the installed height of the spring.Comet says in there manual that the spring has a installed height of 2 3/8 inches and a full shift or totaly compressed height of 11/8 inches with the 102s that is the case ,but with the 108s , they measure 2 1/2 and 1/14 a full 1/8 inch less , so the spring chart is no longer right. Comet says to use the silver spring but that has less tension then the one for the 102s and when you take an 1/8 of an inch away you just make matters worse. I have had good luck with the dark blue polaris spring part # 7041516 & that has been superceded to 7051781 it has a installed weight of 120# and a shift weight of 300#. The 108s and the polaris clutch are measured at the same heights so you are better off using the polaris spring chart . I hope this will help.

Jeff F.

[standupjetski_com]

Bump
After taking my 83 wide open across a lake for the first time I thought,
"thats it, what a dispointment!"
I knew my clutching had to be way off. This topic became very interesting to me. My 83 came with a 108c, silver spring with two washers, and A-3 weights.

My 108c had the "burn mark" that everybody has talked about. I did what "opsled" recommended and removed my primary and secondary springs to see how the belt fit into both clutches. The secondary was definately not opening far enough. I removed some material from the back of my helix using a sanding wheel (see pic). I reinstalled the secondary and now the secondary opens far enough for the belt to reach the top of the primary. While I was at it I threw in a dark blue/white polaris spring (couldn't find a dark blue).

I took it into the alley behind my house and goosed it. The skis lifted off the ground for the first time. Yay!
I then took it to the St Croix River to see how it worked. This thing screams. I went from this last week to this today I'm very happy with how my machine runs...finally. It engages at 4500 and screams to almost 8500. I was hoping for higher rpms but I can live with that for now.
Thanks for all the great advice I got from reading this post. I feel sorry for all the previous owners of my machine who never got to ride it to its full potential.

[vmax-540]

The dark blue &white is the same spring as the dark blue spring , the dark blue spring has been superseded to the dark blue and white .This spring really makes the 108s work like they are supposed to .Comet really missed the boat when they put that silver spring in there. You are right when you say that the 108 come set for a 1 1/4 inch belt on the Vmax so no matter what you do the belt will not go all the way to the top, but when you change it to accept to 1 3/8 belt and change the secondary then it will go to the top. I have been using the 108 sense they came out in 88 and have been really satisfied with there performance when set up right,I have also had good luck with a Aaen orange spring it has a little less full shift tension as the dark blue Polaris so if you want to get your revs down a little from 8500 try it. I am glad to see some one else have good luck with the 108s as they aren't that complicated.

[Vmax540]

Jeff when you say " change it to accept to 1 3/8 belt" what exactly have you done to the 108 and which belt are you using ? Do you know the part #of the Polaris Black Green primary spring ? Thanks Chuck

[Vmax540]

Polaris dark blue and white 7041781 that has a tension of 120lb 300lb

[chrisrider63]

I have polaris clutches on my v-max with A-3 weights and it works amasing. I was out riding one night and started riding with a few guys that were on mach-z 800's, v-max 800's and a z-cat they tested the old v-max but i kept right up to them in the un-groomed farm fields that beast will do about 140 with me on it and about 160 on the road and im 6'5 300lbs. My dad takes it out hes about 170 and the thing flies.

[tyler440]

... i kept right up to them in the un-groomed farm fields that beast will do about 140 with me on it and about 160 on the road and im 6'5 300lbs. My dad takes it out hes about 170 and the thing flies.

are you talking KILOMETERS per hour?!!!!! if thats MPH we need to talk....

[chrisrider63]

Km's

[YAMMIEGOD 3:16]

PHIL, i am gonna throw this post right back. those sleds that lost to that old 78 srx with the vmaxx motor was because they were not clutched right. if they were, no way. 3:16 (YAMMIE TONY)

[Vmax540]

Helix cut 1/16" for use with a 108

[Bob Vehring]

Thanks guys, after 3 weeks of good local riding here, Cat 6000 will be finished tonight, SRV is the next one in, and my VM 600 cyl's came back from plating, just in time for the 40's here now