Polaris RMK 800 snowbike
- Thread starter Brett Kobernik
- Start date
Sound like it might be a good year to get my knee fixed and stay home. Im up in the Logan area. If you ever come up let me know and we can swap rides for a minute and compare.
Best powder experience I've ever had on a snowbike was today. My buddy shot a short video in one of the meadows. The machine is a complete success and it's not even fully dialed.
Been too busy to get anything more done to the project over the last few months. Just been riding it. It's been great. Probably close to 60 days on it now. I've recently made a little progress on the single rail rear suspension. Hopefully test it this week.
Basically, I took the Pro suspension, sandwiched the rails and offset the shocks like Arctic Cat did with the Alpha. I tried to keep the same geometry as the stock Pro suspension so the only real change will be the single rail instead of the standard with skid. It should be plug and play. Might be kinda fun to try it on a sled as well.
Basically, I took the Pro suspension, sandwiched the rails and offset the shocks like Arctic Cat did with the Alpha. I tried to keep the same geometry as the stock Pro suspension so the only real change will be the single rail instead of the standard with skid. It should be plug and play. Might be kinda fun to try it on a sled as well.
Got the skid in place. Feels way different than the stock skid while sitting and leaning in the shop. Go time. Test commences Friday.
Nicely done! Is there some clips added to the center of the track?
Only downside I see from mine is that the bike will bearly stand upright by itself on hard ground... but other than that I don't see many inconvinient, maybe hyfax wear a bit faster on the outsinde edge.
Let us know how it feel on a bigger bike!
Only downside I see from mine is that the bike will bearly stand upright by itself on hard ground... but other than that I don't see many inconvinient, maybe hyfax wear a bit faster on the outsinde edge.
Let us know how it feel on a bigger bike!
No clips yet @fgauvin7. I wanted to test the system out before going all in and removing the old clips and adding them back to the center. I also notice that the bike barely stands on it’s own now. I added two sets of idler wheels which helps this. Not sure if I’ll keep them on or not, time will tell. I need to thank you for your encouragement with the single rail. The test was a success. Pretty sure all my machines will be single rail from now on. Just spun around for an hour or so today to see if there were any serious hang ups. I’m satisfied enough to try a full day ride on it Saturday.
It is very apparent that the single rail has a superior feel compared to standard width skid using a rounded profile track. I’ve been running a 13.5” wide track with a rounded profile. When I put this prototype single rail skid on I also put my 15” wide standard sled track on. Even though this track is wider with no rounded profile, it leans over much much easier/better. Definitely sucks up irregularities in the snowpack much better.
The one minor issue when building this was I had to change the rear shock linkage arrangement slightly to accommodate enough clearance when leaning hard to the right side. This minor change really softened the rear shock and I had to crank it up to compensate. I’ll have to take a closer look at the geometry and make adjustments. It’ll be fine for a ride or two. More observations soon.
It is very apparent that the single rail has a superior feel compared to standard width skid using a rounded profile track. I’ve been running a 13.5” wide track with a rounded profile. When I put this prototype single rail skid on I also put my 15” wide standard sled track on. Even though this track is wider with no rounded profile, it leans over much much easier/better. Definitely sucks up irregularities in the snowpack much better.
The one minor issue when building this was I had to change the rear shock linkage arrangement slightly to accommodate enough clearance when leaning hard to the right side. This minor change really softened the rear shock and I had to crank it up to compensate. I’ll have to take a closer look at the geometry and make adjustments. It’ll be fine for a ride or two. More observations soon.
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Holy ****. Wow. Just wow. OMG, this is a complete game-changer. Had a serious ride today. The single rail excels in every condition. We’ve had 18” of snow this week and it was a legitimate powder day. I didn’t expect much difference in the real soft snow but there is a BIG difference. Complete confidence builder in tight trees. Zero feedback through the skid. Now I can feel the feedback through the wide ski which I never noticed before. Got onto some steep south facing slopes with a firm underlying sun crust. Control was outstanding. Very predictable. The added traction from the full 15” track versus the 13.5” tapered track was very noticeable also. Glad I tried this before cutting a taper into the 15” track. Definitely no need for a rounded track anymore.
The bike already dominated on choppy whooped snowmobile trails but it is really on the next level now. This video shows how the single rail forces the rear idler wheels to pivot away when in the turn making the machine very very agile. It’s interesting how the track can flex so much but doesn’t bind. My buddy related it to ultra low tire pressure in rock crawlers. Unbelievable. The Unicorn is definitely going to get the same treatment. Crazy.
The bike already dominated on choppy whooped snowmobile trails but it is really on the next level now. This video shows how the single rail forces the rear idler wheels to pivot away when in the turn making the machine very very agile. It’s interesting how the track can flex so much but doesn’t bind. My buddy related it to ultra low tire pressure in rock crawlers. Unbelievable. The Unicorn is definitely going to get the same treatment. Crazy.
Spent the afternoon sidehilling. I rode a route that consisted of riding sideways across terrain from 15 to 35 degrees in steepness basically the whole way. 10 miles of sidehilling. I am very intrigued with how this single rail works. Hard to grasp how the track flexes so much and seems to continue rotating smoothly.
I've been following your build since the first post.
I think you've done a very good job.
Keep posting your updates.
Yeah, how in the world can it possibly be, that what I'm seeing in this picture isn't causing major problems? Wild.
Pretty cool to see the future of snowmobiling unfolding right before our eyes.
Nice, this is awesome. I had the same night and day revelation/ experience when I switched to a monorail. This is the way forward. I'm guessing there has to be some amount of power loss from the track twisting, similar to the extra rolling resistance experienced from increased sidewall flex/deformation when airing down a tire for off road, but it must be minimal cause I don't really notice any loss of power while leaning.
Have a zy frame and Camso 129 ... thinking about stuffing a phazer motor in it .. all bottom end and rear exit exhaust .....
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Only problem is the reverse operated by the servo and chaincase ...vs 2s reverse ....
Sent from my motorola edge plus using Tapatalk
Sent from my motorola edge plus using Tapatalk
So, it’s been over 3 months since my last ride. The last ride ended up being one of the best and VERY enlightening. I made one more test mod on my single rail suspension. What I did was got rid of the Polaris style rear shock configuration with all the linkage and stuff and replaced it with a very minimalist strut and Fox air shock connected directly to the rail. Major difference. I liked the Polaris suspension quite well but this test made the bike handle much better. Another game changer. I can’t say I fully understand the standard sled style rear suspension configuration with the linkage and all except that it transfers weight much differently than this shock connected directly to the rail. It doesn’t matter, all I know is this is the way I’ll proceed next season. This was thrown together with steel I had on hand. I’ll take my time and build a nice one out of chromoly or aluminum.
The other thing that I finally got to really test was how the overall width of the machine (the engine is approximately 2’ wide) would handle super steep sidehilling. I wasn’t able to get onto much really steep terrain this winter because of prolonged avalanche danger. Finally things stabilized enough for me to feel comfortable on 40˚ slopes and I really put the machine through its paces. I climbed straight up the slope (loved the power and 15”x3” track) then turned 90˚ and sidehilled back and forth.
The bike handled awesome and the width was no concern.
So here’s the wrap up of what I’ve learned building, riding and tweaking this thing over the last year.
Engine: The 800 2 stroke sled engine and clutches are totally awesome and blow doors on single cylinder dirt bike engines and transmissions (in my opinion). Reverse is really handy. The overall width of the engine had me concerned at first in that it would be too wide for steep sidehilling. Clearly, no problem there.
Rear end: I wanted to try and use the entire rear half of the Polaris Pro. This worked but only with some fairly major mods. 1) I had to increase the seat height by at least 2 inches. 2) I found that using a single rail skid compared to the standard width skid is WAY better. I also found that I had to rework the rear shock configuration to get the best performance. So, yes, you can just bolt on the rear half of a snowmobile to a single ski front end but it’s not ideal. With the mods, it’s totally sick! Oh yeah, I wasn’t sure the 15” track was going to work but it's awesome especially due to the single rail skid.
Front end: Nothing revolutionary here. Third shock is key. The front end feels wonderful. I think there is room for improvement by reconfiguring the entire front end by dropping the height of the head tube and triple clamps and eliminating the tall ski spindle that everyone uses. I also think that the right suspension guy could figure out how to get the stock forks to do what they need to without the assistance of the third shock.
Anyway, I’m looking forward to a few more tweaks to this thing and really hitting it hard this winter!
The other thing that I finally got to really test was how the overall width of the machine (the engine is approximately 2’ wide) would handle super steep sidehilling. I wasn’t able to get onto much really steep terrain this winter because of prolonged avalanche danger. Finally things stabilized enough for me to feel comfortable on 40˚ slopes and I really put the machine through its paces. I climbed straight up the slope (loved the power and 15”x3” track) then turned 90˚ and sidehilled back and forth.
The bike handled awesome and the width was no concern.
So here’s the wrap up of what I’ve learned building, riding and tweaking this thing over the last year.
Engine: The 800 2 stroke sled engine and clutches are totally awesome and blow doors on single cylinder dirt bike engines and transmissions (in my opinion). Reverse is really handy. The overall width of the engine had me concerned at first in that it would be too wide for steep sidehilling. Clearly, no problem there.
Rear end: I wanted to try and use the entire rear half of the Polaris Pro. This worked but only with some fairly major mods. 1) I had to increase the seat height by at least 2 inches. 2) I found that using a single rail skid compared to the standard width skid is WAY better. I also found that I had to rework the rear shock configuration to get the best performance. So, yes, you can just bolt on the rear half of a snowmobile to a single ski front end but it’s not ideal. With the mods, it’s totally sick! Oh yeah, I wasn’t sure the 15” track was going to work but it's awesome especially due to the single rail skid.
Front end: Nothing revolutionary here. Third shock is key. The front end feels wonderful. I think there is room for improvement by reconfiguring the entire front end by dropping the height of the head tube and triple clamps and eliminating the tall ski spindle that everyone uses. I also think that the right suspension guy could figure out how to get the stock forks to do what they need to without the assistance of the third shock.
Anyway, I’m looking forward to a few more tweaks to this thing and really hitting it hard this winter!
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Love it!!! Looking forward to starting a build.
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I obsess over trying to understand suspension geometry only to find out I prefer the opposite of what I thought looks good on paper. Can you explain the feel of the suspension change? My best guess:The pro linkage is very progressive rising rate so it didn't bottom much but will squat a few inches in the beginning under throttle (good for steering a sled in pow). The ts style shock won't squat but is falling rate so will bottom easier. I've tried both on the same bike and like the ts style better most of the time (except big air landings). The progressive linkage seemed to make ski pressure hard to control when it gets steep it would not turn. You can always lean a sled more to jam the ski deeper in the snow for steering grip. So I imagine with only 1 ski and big hp you need more ski pressure than a stock sled skid allows. Great work!
Man, I'm with you. Trial and error is what I end up doing the most.
I think you about nailed it with your description. The Pro suspension seems to squat during acceleration and when climbing steeper terrain. My buddy (sled enthusiast and fabricator) describes it as "weight transfer" but "squatting" seems more descriptive. My take is that you don't want that weight transfer or "squatting" on a snowbike because it tends to lift the ski too much.
The Yamalaris is completely out of hand. 100% success with the concept. Now it’s all about refining. I have lots of tweaks to do still this winter.
I ended up building another pipe. The original pipe was not allowing the engine to reach its full potential because I added a short section of pipe to it and that was throwing off the timing of the sound wave. I did not fully understand how an expansion chamber worked. Now I have a much better understanding. I took another pipe and chopped it up and was very careful to not lengthen or shorten the chamber. I also scavenged up an obsolete Diamond S titanium can made for the 800. The engine is now running at its full “yank your arms out of socket” potential. I still need to tweak the can a bit so it is tucked in under the forks a bit more.
My foot pegs were another aspect of substandard engineering. I’ve been trying to figure out what might be the best option for replacement. Now that the engine is putting out proper power, I’m realizing that I might want to be able to move back and forth on the tunnel. Enter mini running boards. I hacked up a set from one of the donor machines and bolted them on yesterday. Haven’t tried them yet but I have a good feeling they are going to work great.
Another issue I had to address was the worn out center skag on the ski. It was toast from paved parking lots and crossing roads. I went with a very simple single round bar. 5/8” cold rolled round bar, welded some bolts on and some tabs on each end to put bolts through. It’s extended quite a bit longer than the original. I’ve found that this is very helpful for hopping logs. Also, when you hit a rock it grazes over it rather than slamming you to a dead stop like the factory skag does.
I ended up building another pipe. The original pipe was not allowing the engine to reach its full potential because I added a short section of pipe to it and that was throwing off the timing of the sound wave. I did not fully understand how an expansion chamber worked. Now I have a much better understanding. I took another pipe and chopped it up and was very careful to not lengthen or shorten the chamber. I also scavenged up an obsolete Diamond S titanium can made for the 800. The engine is now running at its full “yank your arms out of socket” potential. I still need to tweak the can a bit so it is tucked in under the forks a bit more.
My foot pegs were another aspect of substandard engineering. I’ve been trying to figure out what might be the best option for replacement. Now that the engine is putting out proper power, I’m realizing that I might want to be able to move back and forth on the tunnel. Enter mini running boards. I hacked up a set from one of the donor machines and bolted them on yesterday. Haven’t tried them yet but I have a good feeling they are going to work great.
Another issue I had to address was the worn out center skag on the ski. It was toast from paved parking lots and crossing roads. I went with a very simple single round bar. 5/8” cold rolled round bar, welded some bolts on and some tabs on each end to put bolts through. It’s extended quite a bit longer than the original. I’ve found that this is very helpful for hopping logs. Also, when you hit a rock it grazes over it rather than slamming you to a dead stop like the factory skag does.
Not screwing around with suspension any more boys.
Freaking skid is worth more than the whole machine.
Freaking skid is worth more than the whole machine.
