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Thread: swapping short track to long track?

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    Default swapping short track to long track?

    what does it entail to swap from a 121 track to a 144 or larger track? can i buy a whole track and rail set up and just swap it out, or is there more mod to it?

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    Member tjm's Avatar
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    what machine?.....but yes, pretty much it....
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    Default cat

    i am running a 2000 arctic cat zr 600

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    Going from a 121 to a 144 means you'll likely need a tunnel extension also...

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    That's a sizable jump. Yes, tunnel change, heat exchanger change, suspension change... Pretty much everything from your butt back has to be extended nearly a foot backward (11.5").

    I've done 121 to 136 without problems on early 90's models by just building rail extensions to push the rear axle back 7.5" and install the longer hyfax. The extensions were 3/8" thick by 4" high aluminum plate machined so they bolted to the existing rails and had the adjustment slot for the axles. The axle spacers were cut down to allow for the extra thickness of the material. Cut the heat exchanger in half and weld in an extension. This leaves the hose connections in the original spots while pushing the rear angled portion back further. Weld on some bent aluminum sheet to extend the tunnel rearward and place the bumper back on with the snowflap. Interesting to note that at the time (early 90's) we were cutting the running boards so they angled upward to give more clearance at the rear. Arctic Cat started doing this same thing at the factory a few years later.

    If you're going to do a complete suspension swap, just be wary of the rear mounting point to be sure everything will line up. You may need to do some fabrication at the rear of the tunnel to get things to fit.
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    You mean like the pic attached? That was my xcr stretched 121"-144" with Mountain Machine extensions. I added big wheels (unnecessary), and dropped the rear suspension 1" (big mistake). Only other thing was the tunnel extension OEM new for a 1990 700 RMK; fit perfectly.

    144" on the 121" is about the longest I'd go for a somewhat trail machine; you can feel that extra track back there.

    Going longer would be easiest to buy a complete rear skid and swap it in.
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    Default update

    i have a the 121 extedended out to a a 136, i took it out just to see how it would ride and it seems to to get up and go, i can definitely tell the difference. The one problem i had was it was overheating, no i am blaming this on not doing the tunnel extension yet, does this sound correct?also is there someone here in the state that keeps tunnel extensions on hand. if not does anyone in town make one that i cohuld get cheaper than buying one online, having to ship it to ak, and wait for a week to two to get it here?

    also do i have to extend the tunnel or is there a way to change the heat exchangers and just move them back further. the one son the machine now have a good 8 inches before the rear of the tunnel. and does the snow flap serve any functional purpose other than keeping snow out of the guys face behind you?

    when you go from a 121 to a 136 is it necessary to regear? if so is the regearing done in the chain case and what type of gearing do you choose?

    right now my machine is running a 600efi, if i wanted to swap this out to an 800 or larger what are the determining factors on whether or not the motor will fit with minimal fabrication?

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    Uh...yes, you need the extension, and check at your local dealer. And the flap is there to keep snow in the tunnel so it hits the coolers among other things.
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    Uh...yes, you need the extension, and check at your local dealer. And the flap is there to keep snow in the tunnel so it hits the coolers among other things.

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    Member JOAT's Avatar
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    Turning the longer track is more work for the motor, which generates more heat. If you left the coolers stock, then you're also shortchanging your cooling system on top of the added work. So, a track extension always needs to be coupled with a cooler relocation and/or enlargement. Forgive me if I'm mixing my models, but is the cooler mounted under the rear of the tunnel on this sled? If so, and you left it stock, your track is no longer throwing as much snow on the cooler as you moved the rear axle back. The cooler needs to be in the direct line of fire for the snow that is flying off the rear of the track as it spins upward.

    Tunnel extensions are super easy builds. Any metal worker in town should be able to cut and bend you a U shaped piece of aluminum sheet for this. Best results are usually to weld on via TIG method, but you could get by with an overlap and rivet construction to save money (but not time).

    The best way to handle the cooler is to cut it in half crosswise and weld in an extending section into the center. This leaves the front part where the hoses connect in the stock location and moves the rear edge where it ties into the rear bumper back to the location you've moved it back to via the tunnel extension. It's not too hard to do by a decent welder. A couple pieces of 1/8" aluminum sheet and use 3 strips of 3/16 or 1/4" material cut to get the right thickness of the cooler. One goes down each side and the third runs down the center to divide the coolant flow. That piece gets tacked to the inside of the top or bottom plate. The two side pieces get TIG welded top and bottom to the plates to form a tube. This is then TIG welded back into the center of the cooler.
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    Default coolers

    YES the coolers run under the tunnel about four inches from the sides of the tunnel. Does somebody sell after market heat exchangers that do not have to be fabricated? and who has a fair rate for price for bending me a quick piece of sheet metal and possibly welding it on for me?

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    Member JOAT's Avatar
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    In Anchorage I don't know, but open the phone book to aluminum fabrication or similar and start calling around.
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    Default cooling

    is there aftermarket coolers or do i have to fab and modify the coolers that are on there now?can i use ones off of a different machine that are from a machine with a 136" track?

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    I have done a few swaps and it is not all that bad. Did a 99 zrt600 from 121' to 144", just added rail extensions(have them welded on for extra strength) and made a custon tunnel extension and rode it. Same with a 99 summit X from 136" to 156", same thing,extensions and a tunnel mod.
    I have never cut or changed out the heat exchangers, seems like alot of work. If you chose not to just watch your temp light and make sure your running in a bit of snow.
    As for the motor turning more track, this is true but if you re-gear( some times just a top gear will do to help gear down) you can run the clutching lower to help pull the extra load. If you can keep it as close to stock configuration for clutching the better, 600cc will pull the 144" ok and still run with some bigger sleds if you ride hard.
    Good Luck.

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    Mudman- Take this from a guy that took multiple machines to figure out that mod sleds just ain't worth the coin in most cases. The cost of track, tunnel extension, engine swap etc.. will cost WAY more than just picking up a used 8001m and going riding.

    You are trying to take 10 year old technology and turn it into something modern. You will spend more time wrenching than riding.
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  16. #16

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    You can get a kit or just bend up some aluminum for the tunnel extension. Lift the front of the sled up to see how far the track will travel. You just don't want the lugs grabing the back of the tunnel. The tunnel needs to completely cover the track with the suspension compressed.
    You can buy just the rails if you want. Just unbolt the old ones and bolt on the new longer rails. Extensions can work but are a weaker option. On that model sled you can gain some deep powder performance by drilling and mounting the whole rear suspension back a couple inches. You will get a better track angle of attack and be able to get on top of the snow rather than plowing through it. I ran 144" rails with big rear wheels and 10 tooth drivers and a 156" track.
    Heat exchangers. IF you need them after you get the tunnel extended and the rear flap back on you can get a small rectangular one, mount it in the extension part, and plumb it into the existing system.
    Gearing. Depends on what you are going to do. Trails probably require a couple teeth different from stock. If going verticle, then you want to gear down to maybe 70-90 top speed and then clutch accordingly
    Swaping motors probably puts you in the get a different sled category.

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    I have to disagree with the whole new cooler thing. I had a '97 Ultra SPX SE that was modded for a 2"x144" paddle track using a 700 RMK skid, smaller drivers, removed tunnel protectors and added extension (from 700 RMK donor). Never overheated on me as long as I had snow, and I was the second owner. I also had the scratchers on the rails too.

    My '99 XCR-800 would not overheat unless the snow conditions were poor. You can see in that pic snow wasn't deep at all, but I didn't have cooling issues then. I didn't have scratchers on the rails though as the Xtra-10 skid wouldn't work with them.
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    Default update

    i have bent and made a custom tunnel extension it is ugly but but solid added about ten inches, i will run it like this to see if it over heats if not probs then we are good to go.

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    alright man,

    here it goes i have a 1999 zr 700 that i did the same thing to.
    in my opinion the way to do it is this
    the best bang for your buck is the tracks usa kit. 121-144 rail extentions, tunnel extention, and track all together depending on the track you get is between 675-800 plus 165-200 for shipping. This still beats the price of paying for a track in ak, dollars if you want to go to a lug of more than 1.50 inches you need to drop one tooth on your drivers and change the gears to 24 top and 39 bottom this will bring you back to a stock gear ratio.

    the reason i like tracks usa extentions is they are machined aluminum billet and have a hyfax adjustment. Also they are way more beefy that the western snowmobile parts equivelent.

    now when you do the tunnel ext. make sure to take your time cutting the back of the tunnel out as straight as you can and dont leave out any rivets. because you can mount the stock bumper and snowflap to the extenion.
    also when you put on the rails what i did was go spend 3 dollars at ace hardware to get a couple stainless bolts and flat washers to fill in the original holes fome the back axle (for a cleaner look and extra strength

    and the overheating issue that people were talking about only happens when you dont put the gearing back to stock.


    i hope that answers some of your questions and gives you some references
    either way post some pics when your done i would like to see it

  20. #20
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    Have you seen those odd looking flaps on the sides of the rear tunnel of the Polaris Widetraks? They are a rubber-like material, you could get scrap from Alaska Belting down on Old Seward Hwy.

    Those two things on the side will work great in conjunction with your snowflap for keeping snow in the tunnel. And they cost very little.

    How 'bout some pix?
    Great spirits have always found violent opposition from mediocre minds. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence. Albert Einstein

    Better living through chemistry (I'm a chemist)

    You can piddle with the puppies, or run with the wolves...

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