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.

Snowmobile Cylinder Honing

Someone brought me the cylinders from their Polaris 550.  They had burned a piston and one of the cylinders was a little scuffed up.

This engine has traditional aluminum cylinders with cast iron bores.  These are very robust and can take a lot of abuse.  Modern (or high performance) engines have cylinders that are all aluminum with some kind of chrome or Nikasil plating on them.  Plated cylinders allow for greater engine performance (I think it is due to better heat transfer ability), but they don't seem to be as durable when things blow up.  Once the plating starts to flake off the bore you need to have the cylinder replated or replaced.

For this job I am using a cheap "glaze breaker" type tool.  This tool is inexpensive and available at any auto parts store.  It is not a true hone.  It is only used to fixing minor surface defects.  If you have a cylinder that needs to be resized or you need to fix an out of round condition you need a much more complicated and expensive hone like this.

I normally clamp the cylinder to the edge of the work bench and place a pan under it to catch any cutting oil that drips out.

Put the hone in a variable speed drill and insert it into the bore.  Make sure to coat the bore with a light weight oil.  The hone should be spun at a slow speed and moved up and down while it is spinning.

On a properly honed cylinder you want very fine scratches left on the bore.  These scratches hold a little bit of oil and make the rings seat properly.  The scratches should cross each other at about a 30 degree angle.  You have to get the right combination of RPM and up and down movement to achieve this.  Always check the edges of the ports when finished honing.  The edges should have a very slight radius to them.  You do not want a sharp edge that will catch a piston ring when it comes by.  Normally a small piece of emery paper can be used to clean up these edges. 

Polaris 120 Snowmobile Rebuild

I have an older Polaris 120 snowmobile that I am rebuilding.  The engine had been neglected, so I decided to tear it down and inspect everything. While I had it apart I also removed the governor.  This is the first step to making these machines run faster.

With no governor to control engine speed the motor will rev up until the valves float.  To increase the RPM that this happens at I decided to install a set of "high performance" springs from Recreational Motorsports.  These springs are little bit longer and stiffer than the stock springs.  After the governor elimination this is the simplest way to make more power. The spring on the right is the new one, the original spring is to the left.

Whenever you are assembling internal engine components be sure to coat all the moving surfaces with some kind of assembly lube.  I normally use Lubriplate.

On these tiny motors I use my simple homemade valve spring tool.  You can see this tool and a manufactured one in these old posts here and here.

These small motors motors have a splash lube oil system.  There is no oil pump to distribute the oil around the engine.  The bottom of the connecting rod cap has a long thin "dipper" that sticks down into the oil reservoir.  As the crank spins this dipper splashes oil up onto the cam shaft and around the crankcase. 

Make sure the timing marks are lined up when the cam shaft is installed.  The small punch marks on the edge of the gears are the timing marks.

This photo shows the main parts of the governor assembly.  The governor can be bypassed by messing around with the springs on the throttle linkage, but this puts a higher load on this plastic gear that will eventually lead to it breaking and making a big mess.  If the governor is not being used it is best to remove this gear.  This photo also shows the governor control rod.  I cut it in half and remove the part that goes inside the crankcase.

When installing the spark coil it must be mounted as close as possible to the flywheel.  I have found that the easiest way to do this is place a piece of paper between the coil and the flywheel when tightening the bolts.  When you turn the flywheel you are left with a paper thin space between the parts.

This covers some of the high lights of small engine rebuilding.  When I get the rest of the machine together I will have more photos of chassis work.

Snowmobile Clutch Removal

I had a Polaris 550 snowmobile in the shop that I needed to pull the clutch off.  This first photo shows the back side of the clutch after the job is all done and it is laying on the work bench.  Sometimes I like to make the first photo something that will look good in the little thumbnail size where this blog is advertised over at the Rudstrom Family Blog.

The first step is to get the correct clutch puller and put some anti-seize on the threads.  There will be tremendous pressure on the threads when it is in use and this will help prevent it from binding up.

They are called clutch pullers, but a clutch pusher would be more accurate.  The tool threads into the clutch body and pushes on the end of the crankshaft.  This forces the clutch off of the tapered end of the crankshaft.

The bolt in the center of the clutch is removed and the puller is threaded in.  On this Polaris machine there is a hole placed in the body for this purpose.

The next trick is figuring out a way to keep the engine from turning over while you screw the puller in.  If you have an impact wrench you can simply buzz it in and the inertia of the engine is enough to keep it from turning.  On some electric start machines you can jam something in the teeth of the ring gear and hold the engine that way.

I have found that the best way to hold the engine is with a piece of rope pushed in through the spark plug hole.  Turn the engine so that it is a little way before top dead center, push a small rope into the cylinder until it is full, then turn the engine so that the piston pushes it against the head.

When doing this make sure that you don't start with the piston too far down in the bore or the rope may go out one of the ports.  If using this technique on a four stroke engine make sure that the piston is on a compression stroke so that the valves are closed.

This method works well on small and large engines.  I once used this idea to hold the crankshaft on the engine in my truck when I was trying to change a timing belt on the side of the road.

You normally have to screw the pull in very tight and when the clutch finally lets go it comes of with a bang.  Here is the end of crankshaft once the clutch has been removed.  The shaft is machined with a slight taper that matches the tapered hole on the clutch.  It always seems amazing to me how all the torque from the engine is transferred by the friction on those two tapered surfaces.

Polaris 120 Carb Cleaning

In my last post I talked about drive chains being the number one problem with 120 or mini snowmobiles.  A less common problem is carburetor troubles.  But if you put enough water and dirt in the gas tank it will eventually give you trouble.

The carburetor on this Polaris machine is located on the back side of the engine.  The carb is slides over two studs that are threaded into the engine.  To remove it you need to pop the cover off the plastic airbox and remove two nuts.  The orange colored arrows show the location of the studs. 

Here is the carburetor on the work bench. 

When I pulled the float bowel off the bottom it was full of water, rust, and dirt.

Here are all the important parts.  The blue arrow points to the pin that holds the float in.  It should slid right out to remove the float, sometimes you may have to tap on it

The Green arrow points to the float needle.  On most carbs this is a separate part, but here it is connected to the float.  This needle controls the flow of gas into the carb.  If you have a machine that lets the gas run through the carb and flood the engine your problem is right here.  Occasionally something will get stuck by the tip of the needle and prevent the needle from shutting off the flow of gas.  On my old Polaris 440 I had that problem and when I took the carb apart there was a 12" long piece of musk ox hair stuck there!

The red arrow points to the main jet.  If you have a machine that seems like it does not have enough gas/ only runs with the choke on then the main jet may be clogged.  The jet is made from soft brass, make sure you have a screw driver that fits well if you are going to take it out.

This is what it looks like all apart..  Once the needle/float and the jets are removed I simply scrub it out with a little carb cleaner and blast it clean with compressed air.  Be careful putting everything back together, it is all soft brass and aluminum.

Mini Snowmobile Chain Repair

I recently had a Polaris 120 in the shop.  This is a mini snowmobile designed for kids.  It uses a 120 cc "industrial" engine.  This is a "Briggs and Stratton" type engine like you would see on a lawn mower or other outdoor power equipment.  Arctic Cat and Skidoo also make 120 cc sleds and they are all put together the same way.  There is a simple centrifugal clutch and a chain drive to the track.  The chain drive is the biggest source of trouble on these machines, it needs to be lubricated and tensioned regularly. 

When installing the chain a master link is often used.  They come in a few different styles, but they all work the same.  There is a chain link with a removable side plate and some type of clip to hold it together.  These are quick and easy to install, but are also prone to failing.  Over the years I have had several of them come off on different vehicles.   

A more secure way to connect the chain is with a chain rivet tool.  This tool is used to press the pins in and out of a regular link in the chain link.  It takes a little longer to use than a master link, but will produce a more secure chain.

Polaris Sportsman 500

I had a Polaris Sportsman 500 in the shop with electric starter problems.  It had a few corroded wires and loose connections between the battery and the starter solenoid and wore out brushes on the starter motor.

ATVs around here get used like automobiles in suburban America.  People make lots of short trips around town.  The engine gets started and stopped frequently.  This leads to a lot of wear and tear on starters and the electrical starting system.

This photo shows the brush holder assembly for the starter.  The brush on the top is completely worn out and the lower one is also getting short. 

I change these often enough that I keep a few spare brush sets on hand.  For some vehicles I have the complete brush holder assembly and for less popular models I have a few universal brushes that I can solder onto the original holder.  The universal brushes are cheaper, but the extra time to solder them on cancels out any savings.

C.O.

Polaris Sportsman 500

I recently had my own machine in the shop.  It is a 2008 Polaris Sportsman 500 with about 4000 miles on it.  It was not keeping the battery charged and the tachometer was not working.  The first thing to check in this type of situation is the output from the stator. 

The stator is a series of electrical windings around an iron core.  The flywheel on the engine has permanent magnets in it that surround the stator and  produces an electric current when the flywheel spins.  The power produced is an AC voltage that varies with RPM.  This AC current is converted into DC and regulated to a nominal 12 volts by the voltage regulator.  This is the same basic system that is in almost every small engine.

When I checked the output from my stator with the engine running I got an erratic reading that was very low (7-8 volts) at low RPM.  I then disconnected the plug coming from the stator and tested the resistance on each lead.  I found that one of the leads was shorted to ground. 

I pulled the side cover/recoil housing off the engine and pulled the flywheel to reveal the stator.  This photo shows what I found.  Several of the windings had burned insulation on them and one winding had a few broken wires.  Normally this would mean automatic replacement of this part.  I check around and found that a Polaris replacement part is around $500 and an aftermarket stator is about $250. 

Since this is my own machine and I am trying to be frugal I decided to fix the bad stator.  I cut and unwound the broken wire from the worst spot on the stator.  I then splice the remaining ends together and reassembled it.  When I fired the engine up it started charging fine.  The burned insulation on the other windings has me a little worried about the lifespan of this part, but I think it should be ok for a while.  I may look around for a good used one to replace it with.

C.O.

Polaris RZR Lift Kit

I installed a lift kit on a Polaris Ranger RZR.  The kit raised the vehicle about 2 1/2" inches to allow room to put bigger tires on it.  The $200 kit consisted of these 8 steel plates and a few bolts and spacers.

 It was a nice warm sunny day so I decided to work on it outside.  The person in the photo is Carl, one of the local high school students.  He is working with me this week as part of a vocational training unit at school.

The plates bolt on to the A-arms and raise the shock mount up a little.  I had to use a ratchet strap to compress the springs to get everything lined up.  The whole project took about 3 hours.

Polaris Sportsman 500

I had my 2008 Polaris Sportsman 500 in the shop recently.  A few months ago the headlight that is mounted on the handlebars stopped working.  I did not worry about it too much, I just assumed that the bulb burned out.  Then last week the engine died when I turned the handlebars to the left.  I turned them back straight and it ran again.  I was able to make it most of the way home like this before the engine quite and would not restart.

When I finally got it in the shop and took the handlebars and instrument cluster apart this is what I found.  The lower arrow points to the broken headlight wires and the upper arrow points to the main switched power wire.  A few of the other wires also had cracks in the insulation but were not broken off. 

It was easy to solder the broken wires back together, but I am a little worried about future problems.  For some reason the wires seem to be brittle and cracking where they move with the handlebars.

Polaris Sportsman 500 ATV

I have my own vehicle in the shop today, a 2008 Polaris Sportsman ATV.  My wife was driving it a few weeks ago and she called me and said "something exploded, there is oil everywhere!"  This first photo shows what I found when I went to get her.  The oil reservoir had actually exploded.

These Polaris ATVs have a 4 stroke engine with a dry sump oil system.  Unlike a typical engine with an oil pan or sump on the bottom of the engine, these engine have a separate reservoir to hold the oil.  This allows the engine to be more compact and probably makes it easier to increase the ground clearance under the engine.  I think that it also helps with cooling the engine,  the oil reservoir has a large surface area to dissipate the heat in the oil. (There are probably more reasons than this to use a dry sump, but these seem like the obvious ones.)

I have seen this problem several times before on other peoples machines.  ATVs in the village make a lot of short trips in cold weather.  They do not get run long enough or hard enough for the oil to heat up.  This allows moisture to build up in the oil and the vent line on the reservoir gets plugged with frost and ice.  Once the vent is plugged the pressure builds up and blows the side of the tank off.  Polaris is aware of the problem and has tried to prevent this by putting a small slit in the vent line.  This slit in the rubber hose is supposed to stay closed during normal operation and open up if pressure builds in the line.  Unfortunately it seems like the blockage happens right at the tank and the pressure can not be relieved. 

Another potential problem with the moisture build up is the possibility of ice forming in the bottom of the tank when the vehicle is parked in the cold.  If enough ice forms it can block off the oil supply line to the engine.  This of coarse leads to an oil starved engine and all kinds of problems if the operator is not aware of the situation.

This photo shows the new tank and the original.  It is interesting how the whole side of the tank exploded.  This is the same way that I have seen other ones fail.  I am surprised that the tank doesn't simply split open?

To try and avoid future problems I have decided to insulate the tank to help the oil heat up better in cold weather. 

I cut up an old camping type sleep pad to cover the sides.  I am using DOW 732 silicone to glue the closed cell foam to the tank.  732 is great stuff, I use it for everything.

 Here is the completed tank ready to install. 

Polaris Sportsman 400

Today I have a Polaris Sportman 400 in the shop.  This is the same machine that I put a new recoil starter rope on a few weeks ago.  This time I am replacing the electric starter.

It is a very hard starter to get to.  In the photo I added a red arrow pointing to the starter.  That end is easy enough to see, but the bolts that hold it in are on the other end.  I'll let you know how it goes.
 

Polaris 400 Sportsman

I had a Polaris 400 ATV in the shop today for a simple starter rope replacement.  This is a basic job that only takes 1/2 hour (if you don't let the recoil spring get away from you).

I generally like Polaris products and think that they are put together pretty good.  One thing that I think they do foolishly though is the recoil starters.  Most manufacturers make a simple cover over the pulley with a open drain hole in the bottom.  This keeps most of the crud out and allows any water that gets in to drain out.

Polaris makes a cover that is supposed to be sealed up water tight.  It never works out that way and a little water always makes its way in.  Without an open drain in the bottom the water stays inside and everything ends up a rusty mess.

That is how I found this one.  Everything still worked under the cover, but it was wet and rusty.  I had to spend a little extra time cleaning things up before I put it back together.

Polaris 500

Today I actually have my own four wheeler in the shop.  When I was driving fast on the beach this morning the drive belt broke.

It is a simple thing to fix, 10 bolts to take the cover off and there it is.  Unfortunately I did not have a spare belt here and I had to call the dealer in Nome to get a new one.

C.O.