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.

Exhaust Spring Tool

Most snowmobile exhaust systems are held together with springs.  The springs allow the the parts to move around with temperature changes and engine movement but always remain in tightly connected.

Removing and installing these springs is easy if you have the right tool.  Here are two spring tools that I made.  One of them is made from an old screwdriver that I ground two notches in the blade.  One is for pulling and the other for pushing.

The second tool is made from the wire handle from a 5 gallon plastic bucket.  The ell shaped bend on the end is originally from where the handle connected to the bucket.  It is just the righ shape to grab the end of a spring.  I put a piece of plastic fuel tubing over the wire to make a softer handle and then bent it into a loop.  This is my favorite spring tool.  It looks crude, but works great.

Shop Tip - Melting Snow

I frequently have to thaw out machines that are packed full of snow before I can work on them.  When the snow melts the water makes a big mess on the shop floor.

To avoid most of the mess I like to put a piece of construction type plastic sheeting under the machine.  I then roll the edges up to form a sort of dam and clamp the edges to the machine or some other type of support.  When the snow melts it is all contained on the plastic.  I then use a wet/dry type shop vac to suck up the water.

Traveling - Nome

I recently spent some time in Nome at my friend Roger's.  You may remember Roger from my house jacking project this fall, or you may have seen him lighting a fuse over on my family blog.  Roger helped me out with the house so I came into Nome to help him out with a few mechanic jobs.

Roger has a Polaris 550 with a lot of hard miles on it.  Almost all those miles have been across bumpy tundra pulling a big sled.  When the machine was new Roger built this tow hitch and fuel can rack for the back.  It is made from 1/4" steel plate and it has held up fine.   Unfortunately the aluminum tunnel that it is bolted to is starting to crack in half.

I took everything apart on the back of the machine so I could straighten out the bent and broken tunnel.  Once I had that back together I welded up some longer braces for the tow hitch.  The hitch now has two pieces of flat bar that run all the way up to the foot wells. 

Snowmobile Tow Hitch

In the winter our primary means of transportation is by snowmobile.  Most of the time when you are snowmobiling here you are pulling a sled.  All of this sled pulling puts a lot of wear and tear on the tow hitch.

The factory made tow hitches that come with snowmobiles are never tough enough.  I replace a lot of them for people.  Here is a collection of broken and wore out hitches.  Many of these are the type that fit into a tube on the rear bumper and they are held in place by some type of pin.  The pin is never strong enough, it eventually bends.  Frequently the hitches are made from metal that is too thin or they have inadequate welds.  Another source of trouble is the latch that keeps the sled connected, the springs fall out or the latch bends.

Over the years I have come up with a replacement that solves all of these problems.  I build my tow hitches with a 1/2" clevis, a 3/4" bolt and a nyloc nut.  If you use a quality clevis they are made with an alloy steel that seems to wear better than the typical mild steel factory units.  The shape of the clevis also makes for a better tow hook than the usual "J" hook.  The clevis is narrow at the top and keeps the sled draw bar from coming out.  The shape works so well that I often don't screw the clevis pin in the top.

After grinding the galvanizing off the clevis I clamp them together for welding.

This is a very important weld that must be done carefully.  These are the tools that I use to clean the slag off between weld passes.  The top three are typical welding tools, but the bottom one is one of my favorites.  It is a standard Stanley awl.  If you hold it loosely with one hand and tap on the end of it rapidly with the wire brush of the side of the chipping hammer it acts like a mini needle scaler.

Here is a close up of the completed weld.  An old well driller that I used to work with would say that a good weld "looked like a stack of dimes."

This is the completed hitch.  The nyloc nut holds it much more secure than a little pin through a hole.

Here is the new hitch on the back of a Polaris.

Arctic Cat F6 Sno Pro

Today I worked on a 2010 Arctic Cat F6 Sno Pro.  The owner brought me the machine because it would not start.  He suspected a fuel problem (normally I don't listen to what the owner says, but this time he got it right).  I pulled the rope a few times and the engine did not fire.  I pulled the spark plugs and checked for spark, then squirted a little fuel in the cylinders.  This time when I pulled the rope it fired up for a couple of seconds.  Definitely a fuel problem.

This machine has a modern engine with a battery less fuel injection system.  When you pull the rope the stator makes enough electricity to charge a capacitor and run the injection system.  I pulled the fuel line off the injector rack and checked for fuel pressure when pulling the engine over.  There was no fuel pressure so I decided to check the voltage to the fuel pump.  I found the wires going to the pump and checked for voltage when cranking.  I saw spike of 15 volts when pulling hard on the rope and it then gradually dropped off.   All these signs point to a bad fuel pump.

The pump is mounted inside the tank very much like a typical automotive system.  Just like working on cars, it is a pain to get to the pump.  I decide that I would like to do one more test to make sure it was the pump before I pulled everything apart.  In the photo you can see my temporary fuel system that I rigged up to run the engine.  I have a "Hudson" type garden sprayer filled with gas, I pumped this up to 15 psi (thanks Dave for the help) and connected it to the fuel rail using a few plumbing fittings and tubing.  With this setup supplying the fuel pressure the engine ran OK.  I later learned that the system is supposed to run at 40 psi, but 15 was enough for testing in the shop. 

Once I was sure that it was a bad pump I pulled everything apart and took the pump out of the tank.  Now I just need to find a replacement.  The Arctic Cat dealer only sells the complete pump assembly with the mounting bracket and fuel level sensor attachment for $450!  The pump itself is a basic Walbro like automobiles have, normal price $80 -$100.  Hopefully I can find a source that will sell me just the pump.  Any one have any ideas where to look?

C.O.

Skidoo MXZ - Completed

Today I finished up the Skidoo MXZ 600 that I have had in the shop for a few days.  The total time for the project was 10.5 hours.  There was about 3 hours to take everything apart and pull the engine, 3 hours to fix the wiring problem on the stator, and 4 hours to clean the engine bay and put it all back together.

  Here is a closeup photo of the burned section of the stator wire harness.  The end on the right went to the stator and the other end went to a plug.   I assume that Skidoo buys the stator from someone else and it comes with short leads on it.  Skidoo then adds the longer wire with the correct plug to fit the wire harness.  If you look close you can see the original crimp connectors that came from the factory.  I suspect there must have been a faulty crimp on one of the wires.  This is the second machine that I have heard of with a problem with these wires. 

To repair it I simply cut out the bad section of wire and spliced in a few inches of new wire.  I used basic butt splice crimp connectors that I crimped and soldered.  The splices were then sealed up with heat shrink tubing.

C.O.

Ski Doo MXZ 600 - Update

 I removed the engine from the Skidoo MXZ 600 that I have in the shop.  It is almost 3 hours of labor to get the engine out.  This is not an easy machine to work on.  There are a lot of tubes and wires crammed into a small space. 

The wires that come from the stator are broken and shorted out where they exit the crankcase.  The red arrow in the first photo shows the location.

This second photo is a close up of the wire problem.  I am hoping that I can take it apart and splice the wires back together.  The stator is a very expensive part and I would like to avoid replacing it.

Ski-Doo MXZ 600

Today I have a 2006 Skidoo MXZ 600 H.O. in the shop.  This machine has some shorted out/ burned wires that need to be replaced.  Unfortunately I am going to have to pull the engine to get to them.  I have worked on this machine before and I have to say it is one of the most awkward and annoying vehicles to work on.  Everything is crammed into a very small space and it is hard get at anything.  It does run great and go very fast.  I guess that is the trade off, light weight and high performance versus easy to service.

I would also like to comment on snowmobile graphics.  Who designs the graphics on these things?  They take the most outrageous colors and styles from 10 years ago and splash them together.  Why do people like these things, and why do they buy very expensive jackets to match?

Skidoo Mini Z 120

Harold and I are getting his snowmobile ready for the season.