120 Track Driver

I have several 120 cc snowmobiles that we use for racing and playing.  These are small childrens machines powered with "lawn mower" type engines.  All of the major manufacturers sell these machines and they are all put together with very similar components.  I have a few older posts about them here, here and here.

These machines use a 12" wide track that is normally driven with involute drivers that engage the track on the rubber "lugs" on the inside of the track.  After a lot of hard use the track and drivers on our Skidoo Mini Z wore out.  In this photo you can see the lugs sticking up on the right side of the track, just outboard of the clips.  The left side of the track is supposed to have lugs also, but they have all been ripped off.  This track is interesting because there is no windows in the track.  The clips are attached to the track with no open holes.

This photo shows a Polaris track with nice tall lugs next to the clips.  You can also see that there is a "window" between each clip.

The track in the Skidoo was obviously junk and the drivers on the drive shaft were pretty worn out.  In the above photo you can see the old drive shaft on the right side (I cut it in half to make it easier to get out of the old bearings.)  As you can see the teeth on the black plastic drivers are rounded off.

The drive shaft on the left side is a Polaris shaft with new "anti ratchet" type drivers.  These drivers are designed to drive the track be engaging the windows on the track and pushing on the clips.  This set has 5 teeth rather than the original 4, this will change our gear ratio quite a bit, making the machine faster on the top end but given up some low end torque.

I ran out of photos, but the new Polaris track and drive shaft fit right into the Skidoo with no problems.

Rev XP Brake Replacement

For many years almost all snowmobiles were put together in the same way.  It didn't matter what factory it came from , when you opened the hood the pieces were all in the same place.  In recent years there has been a big push to make the machines lighter and more compact.  This has resulted in a lot of changes in the layout and arrangement of the chassis and drive train parts.

The red arrow in the first photo is pointing to the cover over the brake disc on a newer Ski Doo Rev XP machine.  This ones happens to have a 550 fan cooled engine, but all the Rev chassis machines have the brake in this location.  I have seen a few of these get stuck from a build up of snow and ice around the brake rotor.  While riding fine snow can blow in on the hot brake rotor and melt, when you stop for a coffee break it cools off and freezes.  When you try to take off the machine won't move because the brake is frozen in a block of ice.  If you have one of these keep an eye on it.  Make sure you have the correct size Torx wrench in your tool kit to get the cover bolts off.

This particular machine is in the shop to get the brake rotor and caliper replaced.  Someone drove the machine around with the parking brake set and the brake heated up so bad that everything was destroyed.  This is the second time I have seen this happen this year!

Here is the new brake caliper/drive shaft bearing mount.  As part of the effort to save weight and package everything smaller Ski Doo has made the bearing mount part of the brake caliper.  The bearing sits in the large opening, and the four smaller holes bolt the assembly to the side of the tunnel.

This is the bearing and the end of the drive shaft where it sticks out of the tunnel.  In the old days almost every machine used the same 1" bearings for the drive shaft and the jack shaft.  As you can see in this photo the drive shaft is hollow and uses a large diameter bearing.

Before installing the new bearing mount I heated it up with an electric heat gun.  This causes the metal to expand and increase the size of the hole that the bearing fits in.  On many bearing mounts heating like this can increase the size enough to eliminate any pounding or pressing to install the bearing.

The brake line is connected to the caliper with a banjo bolt.  Make sure you install it with two copper crush washers, one on each side of the fitting.  Once the line is connected the air must be bled out.  See this post for info on how to do that.

Here is the new brake all assembled and waiting for the cover.  Remember if your machine feels a little sluggish make sure you don't have the parking brake set.