FCX Fan Cooled Xtreem CMX

Mounting position for the Pro RMK skid

I had some one ask what the mounting position is for the 2013 Pro RMK skid. I have attached the measurements I am planning on using. I took these from my 2013 PRO with the skid still in place. If I remember correctly the measurement from the top of the tunnel is to the sheet metal part of the tunnel not the bottom of the heat exchanger. If anyone has taken them and came up with something different please let me know.

The first drawing I posted has been corrected. I had the 30 7/8" measurement shown going to the drive shaft centerline. The 30 7/8" is from front arm to rear arm mount position.

I found some cracks in the bulkhead so I got a new one sent out from Mark at CMX. Cleaned up the drive shaft and painted it. Finished the belt adjuster but I have started working on something a little different that may save a few oz. If that don't work out I will use what is in the pictures. Project has stalled, as work is where I live lately. I will keep you updated when I get back at it.

Not much progress on this as work has consumed much of my time. I have been working on revising the belt drive design. When I got the new bulk head I just did not want to open up the bottom of it like it was for what I had so far. Using the narrower Jack shaft and drive shaft from the newer sleds required mounting the bearings inboard. This required a large opening in the bulk head for the drive shaft and moving the jackshaft up from the stock location, which reduced the amount of drop and roll, and track clearance at the bulk head. I am still drawing new parts that will allow outboard bearings, will not require opening the bottom of the bulkhead, and leave the jackshaft in the stock location. I will be using the longer splined jackshaft from a 2012 pro rmk, this will require a larger ID bearing and a custom spacer/sleeve that will give more support than just having the shaft splines support the bearing. Had to do a bunch of research to find a bearing that would work. Also will be using the lightest 2013 pro drive shaft and make a spacer for the PTO side of the tunnel to make up for it being too narrow. The plan is to include seals on the jack and drive shaft bearings with a grease port that will push the grease from the inside of the sled to the snow side to be able to push the water from the bearings. I found a 550 sport that I am considering taking the engine from instead of the 440 I have now. I will update when I get more done on the belt drive. Added a picture of where I left off with the lighter belt adjuster. I may need to revise this one also to go with the changes to move the bearings out board.

Got some parts made. Here are some pics.
#1 2012 Pro jackshaft. Longer than the 2013 with the extra width in the splined area of the belt drive side. New bearing mount with provision for grease seal and zirk. Seal sleeve / spacer for lip seal to ride on. Larger OD/ ID bearing than a 6205. Stepped spacer to be interference fit into the bearing. Will get support from the splines as well as the unsplined area of the shaft.
#2 2013 Pro Drive shaft. New bearing mount with provision for grease seal and zirk. 6205 bearing. New spacer for the clutch side of the drive shaft with provision for grease zirk. Will need to remove the seal from the bearing.
#3 drive shaft spacer installed. We will see if it will be possible to install and tighten those flangette nuts with the track installed.
#4 Drive side. The pulley hub will need to be turned down for the seal surface.
#5 Jack shaft assembly with the spacer installed in the bearing and bearing installed in the support mount. Due to Polaris using a fixed location pressed on bearing, there is a .120" driven clutch shim washer between the jackshaft shoulder and the stepped bearing spacer. The .120" space will be used to shim the jackshaft for zero bearing side loading with different size shims.

Finally have been able to get back to this project. There was a long span where I had no time to work this but it has been on my mind this whole time and I have been working on it my head. I made some revisions on the belt drive plan when I found the new Axys style (PTO side) bearing flangette on the drive shaft. Planning on using the lighter pro drive shaft just like before but the spacer needed to make up for the older sleds wider tunnel will be different than what I had made, and will require a redesign. See pic #3 in former post. This will simplify installing the drive shaft by using longer thru bolts from the under hood side of the bulk head thru the bulkhead thru the spacer and into the flangettes. Was able to get a new back plate made that will put the brake toward the back instead of the forward mounting the first proto type had. It has been slow going but here is some pics of recent progress.
#1 Plate with type of flangette that will be used on the other end (PTO side) of the shaft.
#2 Plate with studs installed for bottom bearing support.
#3 Plate with bearing supports installed. Note: recessed holes for rivets that will attach plate to chassis. Paper Prototype of new belt adjuster bracket.
#4 Plate with bearing supports installed. Note: rework on lower bearing support for revision to use new axys style drive shaft flangette.

Made some progress.
#1 Back plate. Socket shows where the belt tension idler will mount.
#2 Filling up previous cut outs from stock, cmx drive, and my first prototype.
#3 Jack shaft installed into new metal.
#4 New part for drive shaft mounting. Combo of a flangette and spacer to allow use of the shorter pro drive shafts.
#5 Part was around one pound when completed so I took a few Oz out of it. Will most likely clip the bottom off and hope to get it down around 8 oz. The missing hole on the inner bolt circle will be where the grease passage will be cross drilled.
#6 Bearing/ spacer/ flangette assembly. Two tapped holes will get studs to mount this to the inside of the tunnel.
#7 Installed spacer/ flangette. The thru hole would allow for a modified 1 1/16" hex shaft to be used. The thru hole in the bulk head was made smaller than stock so I could get the shaft as low as possible with out notching out the bottom of the bulkhead as was done in my prototype. I was able to get 6.875" shaft centerline from the top of the tunnel. The spacer is bored to accept a seal. Will need to make a shaft extension that will be attached with some all thread to the end of the drive shaft much the same as the dragon drive shafts attached the speedo counter. This will allow for a modified right angle spedo drive to be attached to the two studs that are holding the adapter to the tunnel.
#8 First mock up of adapter install. Patch plates not finished riveting yet.
# 9 Installed Drive shaft.

Installed upper and lower TKI sprockets. Bottom sprocket hub was modified to fit my bearing holder and to have a place for the grease seal to ride. If you look at earlier picture of the bottom sprocket it has a tapered hub. Machined some of the taper away to a straight OD back about 3/8". Did some straight edge line ups on the sprockets and needed to make some minor adjustments to the mount positions of the clutch side of the drive shaft as well as the jack shaft. As the bulk head is a weldment it is not perfectly square. For this install I have drilled the back plate to line up with 6 holes in the bulkhead and plan on riveting it to the side of the tunnel (It is currently bolted with 10-32 screws). As these six holes are common to both sides of the sled I used the back plate (without the bearing supports attached) on the clutch side to locate the holes for the jackshaft and drive shaft. The drive shaft ended up perfectly square to the tunnel on one side but a little off on the other side. I would have rather split the difference but this would have required me to shim the back plate with some shims on the front side. The issue with doing this is that I have six attachment points on this plate and it would be difficult to get the correct amount of shim under multiple attachment points. This is probably why most Polaris chain cases were mounted with only three bolts so shimming the chain case for perfect shaft alignment (square) to the tunnel was much easier. If I do another one of these I think I will use the same rivet holes to locate the plate on the belt drive side, and to locate the upper and lower shaft positions on the clutch side, but then use four bolts on the outboard corners to attach the back plate to the tunnel. The alignment holes would then be countersunk on the tunnel side of the back plate to allow the rivets to be reinstalled to hold the tunnel to the bulkhead. This would allow for shimming the back plate at the four corners to make alignment adjustments. For squaring up the shafts to the tunnel I started with the bottom shaft first. Put a .030" shim between the bearing and drive shaft to let the bearing holder sit outboard just slightly from the back plate and saw that the gap was uneven front to back and top to bottom. Opened up the mount holes on the clutch side with a file to let that side of the shaft come back and down a little till the gap was even. Then measured the gap and replaced the .030" shim with one that got me to zero side load on the bearing (Mc Master Carr has a wonderful selection of Metric stainless shims in .004" to .059") . Then some checks with a straight edge between the top and bottom sprocket showed that the jack shaft needed to be moved almost the same amount in the same direction. No tensioner on the belt yet but it is tracking well when turned one direction, and is starting to walk off after many turns when spun the other direction. It is very close but may need to some more adjustment after I finish putting some rivets back in that were removed and get the belt under some tension. All this adjustment was done with the front skid shaft installed to get the tunnel width the same as it will be with the rear skid installed. Still need to fill in the large hole around the pulley and the side of the tunnel under the back plate.

I might have missed it in previous posts but what is the gear ratio of your belt drive?

With the current shaft centerlines possible combos are as listed bellow. I think I can get down to the 3.00 to 1 with the current adjuster if needed. Teeth in mesh and the smaller outside diameter on the 21 and 22 may start to affect belt life at higher horse power levels. The 27 tooth should fit but most likely would not even need any idler tension. Just depends on how accurate my actual center to center distance came out to what was planned. I have TKI sprockets 63, 26, and 25 that are set up for the pro and will work with only a mod to the outer belt guide. I have a TKI 24 tooth from his chain case conversion kit that can be modified to use, and some bar sprocket blanks to bore and broach for a 23 and 22 tooth count. I believe I may be able to source some 21, and 27 tooth stock also if needed. The set up shown is 26/63. With the low horse power of the fan engines I think I will need to start at the 2.52 to 2.62 range. Polaris geared their Indy sport GT 141 nub track at 2.44. If top speed at full shift out ended up at 45 MPH but it still is able to turn a deep lug track in deep powder that would be fine by me.

27/63 2.33
26/63 2.42
25/63 2.52
24/63 2.62
23/63 2.74
22/63 2.86
21/63 3.00

Also, what size / pitch drivers will you be using?

I am planning on using 3.00 pitch 8 tooth involute drivers with a 141 cobra 1.6 lug track. If I stay air cooled a Power claw would also clear. Adding tunnel coolers for a water cooled engine would be close with a power claw and may require 7 tooth drivers. My shaft centerline should be just under 7 " from the top of the tunnel, same as I have measured on a pro chassis.

For my track choice of the 141 cobra 1.6 lug I considered a few things to pick it.
# 1 It is light only 41 lbs.
# 2 I have read that it works very well in powder.
# 3 Polaris used a 1.25 lug 136 on trail RMK for many years that got rental sleds around in the mountains. Granted they did not go everywhere the top of the line RMK did but they were still capable 500 plus pound sleds.
# 4 I had a 700 SKS 1.25 X 144 that I rode out west as a spare and while it had its limits in deep snow it could get around.
# 5 My final finished sled weight should be much less than all I have compared this to. The lower HP of a 440 will not perform as well as a 550 or 700 but the lower sled weight should equal some of that out. The rider when its not me will be much lighter also. This could all be wishful logic so there is also the option to up grade to a 141 powerclaw 2.25 (around 46 lbs). And now there is the new super light 155 2.6 (46 Lbs ?) option. O ya and could someone please tell me again why Polaris wont build a sub 400 Lb sled on the pro chassis, snow check special order only, with parts off the shelf ? They do seem to have figured out how to take orders and put sleds together with different shocks, engines, tracks, colors, and other options, all with parts off the shelf so I know it can be done in limited build numbers. O boy I got off track there for a minute, back to the build.

Started filling the holes in the bulkhead on the mag side from previous install of cmx drive and my first prototype. After fit up this will be riveted back together with counter sunk aircraft rivets to allow the belt drive plate to sit flush to the bulkhead. Was able to get the area where the trailing arm mount to back to flat again.

#1 The extra large hole with some bent aluminum from a previous trailing arm mount incident.
#3 Cut out of tunnel material. .060" thick material.
#2 Cut out of bulkhead material. .095 thick material.
#4 Donner material for tunnel repair.

Making Progress but still have a long way to go.

#1 New patch material cut and fit up.
#2 Patch riveted in with flush rivets where needed to allow drive plate to set flat against the tunnel.
#3 Inside of tunnel patch.
#4 Drop bracket paper prototype.

Now I will need to put some new holes into that fresh material for the drive shaft and the clearance needed for the bottom pulley. Still need to make the new belt tension bracket and finish parts to make greasing the bottom bearing possible.

For now the 440 will go in stock but there are still some details to work out on getting it mounted into this bulkhead as Polaris does not make a mount plate that is a direct fit. I have a plate that may work with some different thickness motor mounts but may not put the engine in the correct location for belt length and offset. I also have a 550 plate that could be drilled for the 440. I did purchase a pipe for it that could make its way onto the sled. Did not weigh it yet to determine how much can be shed by running it. Sound will also be a factor on the pipe.

Started looking at where the skid mounting points will end up. With the current running boards and the CMX tip up tunnel this drop bracket would be extremely long. I am looking at using some PRO running boards to replace the CMX ones. They will require some mods to get them to work but will move the tip up on the running board back so the rear skid arm mounts will be closer to stock Pro drop bracket length. With the Pro rear skid mounting so far out of the tunnel the tip up tunnel does not really seem to be as necessary as it once was with the older skids. Made up a paper prototype drop bracket that will be made from sheet metal similar to the Axys. It will use more material than the stock one due to the boxed design that will not allow it to collect ice like the stock one does, it will also cover more side tunnel surface to strengthen it, and it needs to be a little longer.