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post #1 of (permalink) Old 12-13-1999, 04:24 PM
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650 cluching & gearing

I'm looking for advice to improve the off the line acceleration for my sled.

I have a 1990 Indy 650 that always used to have more power than I needed. Normally it was limited by traction. I recently installed a Aggressor 1" track...

This track sticks like glue and even with the suspension set up to not lift the front end and me leaning forward, on the right snow it will lift and keep lifting (around 30-40 mph). The machine absolutely flies (acceleration wise). Top speed is down a few mph though (but I love the traction, so I'm happy).

The problem is now the machine is missing a little from about 0-10 mph (not much - but it could be faster). I tweaked the clutching to bring the engagement RPM from 4200 up to 4600, and it's better, but it's not enough (I weigh about 210 & some of my friends still pull away off the line a little). The max RPM is still set at 8200.

I figure I could either bump the engagement further to 5000 , but I really like the drivability the way it is. I'm contemplating changing the gearing from 21:35 to 19 or 20:35. I'm worried about not having enough clutch gearing to keep my 100 mph top end (without revving over 8200).

Does anyone know how much more room (gear wise) there is on the clutching? I figure the primary and secondary clutches are pretty much maxed out at 100 mph at 8200 rpm, but all I need is 6% gear remaining to run 19:35 sprockets. If there's no room then I guess increasing the engagement rpm (or tweaking the motor) is my only option. I'm going to try tightening the belt a little beyond spec, but I don't know how much that will improve things.

I'd appreciate any advice/info.

Steve

Steve S.
http://home.off-hoad.com/~ovo/members/sshaw/sshaw.htm
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post #2 of (permalink) Old 12-13-1999, 08:41 PM
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Re: 650 cluching & gearing

I have a 1992 Polaris Indy 650 RXL. My sled is also is faster than hell. You can ride at 25mph and punch it and still lift the skis off the ground. Or you can go from a dead stop and punch it and keep the skis off the ground until 40-45mph. Keeping in mind that my sled has about 119 pics in the track. My sled I bought clutched already from a polaris mechanic. I will email him to night and ask what weights and springs he put in the clutch. And then post it on this postboard. Its nice to know that the 1991 and 1992 Polaris Indy 650's are still around. talk to ya latter,bean

post #3 of (permalink) Old 12-13-1999, 08:58 PM
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Re: 650 cluching & gearing

bean, how fast have you had that thing?

Keith
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<font color=blue>89 Yamaha SRV</font color=blue>
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post #4 of (permalink) Old 12-13-1999, 10:41 PM
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Re: 650 cluching & gearing

Well I emailed him and he replied saying that he wasn't sure of what size the weights and springs are because him and his friends tried a couple different combinations. He siad the reason he switched them was becuase he wanted to get better 0-60. And because when he would max it out it would max at 103mph. And he said that the rpms where way to high. And that the sled wasn't riding the power band as much as it could. So they played with the springs and got it so that the sled would ride the power band as long as it could. That is why it can still pull wheelies at 25. I personally have only had it going around 70mph. But that was with out a helmet and it was the first snow fall I had to ride it good. Keep in mind that know that the sled has different weights and springs it max's out at around 107-110mph. Wich is pretty fast for that sled. And you also have to remember that these speeds are the actual speeds that where taken on a radar gun. Because the speedometer only goes to 85. And he said that when you barry the needle you are really only doing like 80 on the radar gun. thanks,bean

post #5 of (permalink) Old 12-14-1999, 12:11 PM
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Re: 650 cluching & gearing

Bean, it sounds like your machine is set up right.

I've had my machine up to about 103 mph on a hard packed river. I say about because I didn't actually radar my machine, but a friend radared his Mach 1 at 103 the day before (with his speedo reading over 110) and flat out we were side by side (we couldn't believe how close the top speeds were).

What bugged me was if we took off with a standing start over the first 15 feet he would gain about a snowmobile length on me and stay there all the way up to 100 mph (I did gain a little back in the 40-70 mph range though).

At the time I was still running the 0.75" track and limited by traction. With the new track he still takes me on the first little bit, but then I smoke him up to around 90 mph and then he starts slowly gaining and eventually passes me.

Bean, what RPM does your clutch engage at? What does it max out at during full throttle acceleration (not at top speed)? Did they change your chaincase gearing at all?


Steve S.
http://home.off-hoad.com/~ovo/members/sshaw/sshaw.htm
post #6 of (permalink) Old 12-14-1999, 04:12 PM
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Re: 650 cluching & gearing

No there was no chaincase modifications that I know about. I don't know for sure but I think the sled engages at either 4,000 or 5,000 rpms.

post #7 of (permalink) Old 12-14-1999, 06:58 PM
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Re: 650 cluching & gearing

Crank up the engagement to at least 5000 and I ran mine at 8700 - an occasional over 9000. 9 and over is just fine but be sure to check your circlips and replace them often. While you have the jugs off clean up the ports and smooth them out no need to remove any material just polish it out. It'll wake up and surprise you

post #8 of (permalink) Old 12-15-1999, 11:07 AM
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Re: 650 cluching & gearing

Everyone I've known to run an Indy 650 around 8700 rpm has broken piston skirts (you haven't had any problems?). Mainly because of that I decided to keep the stock pipe and keep the max rpm to around 8200. I'd like to bring the engagement rpm up to 5000 though.

My original engagement was at 4200 (actually down to about 4000 after 3000 miles), but I noticed a friends stock 1992 650 engaged at 4600 and had the same 8200 max rpm. Not being an expert on setting up the clutching I simply copied the 92 model and installed all of the springs and weights for that year in both the primary and secondary (that was 4 years ago). It worked (4600 engage, 8200 max), but I just checked my engagement rpm and (after 2500 miles and 4 years) discovered it's back down to about 4300 so...

Is there a web page or book on setting up these clutches that can give me some equations or at least the general relationship between springs, weights, ramps, etc.

I'm still also tempted to go the 6% reduction (as well) in chain sprockets (19:35 instead of 21:35) that should give me 6% more torque at the track off the line and get the machine into the higher rpms faster.

Any clutching guru's out there?

Steve S.
http://home.off-hoad.com/~ovo/members/sshaw/sshaw.htm
post #9 of (permalink) Old 12-15-1999, 09:17 PM
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Re: 650 cluching & gearing

Steve here is my 2 cents. I had a 91 model 650. Have you had the clutches inspected lately? They have to be tight and in good shape to get performance. very important on the old piston port engine is clutch to belt clearance. Many bogs can be attributed to this. Get it to about .015" to .020". Buy new springs for sure, they sack out during use and time. A helix is in order also. Mark your clutches and top it out to see if you are opening them fully. If not you can gear down and keep the same or even gain a bit more top end. Try this setup- 21-39 or 22-39 gear (66p chain), 10al or even 10a weights, 145/300 spring, 46-36 helix, red pol spring in 2nd hole. Use the secondary spring to get the backshift you want then the weights to run the rpm you want. I ran mine at 8000. If you need a stiffer sec spring the pol silver/blue is a good one. Try an overdrive setup if you want to try for acceleration and top end. These are some ideas for you, have fun!

post #10 of (permalink) Old 12-15-1999, 11:17 PM
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Re: 650 cluching & gearing

The clutches are in good shape. I just checked everything out and although the primary spring seems about 0.2" shorter than when I installed it, everything else is tight and in good shape.

What did yours engage at? (if you remember) What sort of top speed were you able to get when overdriving the clutches and running 21-39gears?

Ijust ordered Olav Aaen's Clutch tuning handbook. Hopefully it will give me enough info to really get this thing set up.

BTW,currently I'm running 0.020"belt clearance, 10AL (53g) weights, the blue spring (If where I bought it is right it's 165/260lbs), stock 34helix, and red secondary spring in 2nd hole.

Comparing those to yours I should have a higher engagement RPM because of the 165lbs initial spring load (when the spring was new 4600 was the engagement rpm). With this setup I was originally happy with the off the line performance. What created the "bog" was running the sticky 1" track instead of the stock 0.7" Polaris track. Whereas before I could punch it and immediately the engine would scream to 8200 with the speedo reading 50mph (spinning track). Now I can only just spin the track for the first 20feet or so until the engine gets into it's power band and then the machine leaps into action.

Thanksfor all the info. I have friday off and I'm supposed to get the book that morning. I figure I'll take apart the clutches and measure the spring forces and start reading.

BTW, part of the reason for me finally trying to get the clutching optimized is a friend of mine just picked up a 1998 Cat ZR 500 and I want to at least not be blown away by him. It's been bugging me for a while, but now it's time...


Steve S.
http://home.off-hoad.com/~ovo/members/sshaw/sshaw.htm
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