Sunday, November 27, 2011

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.

Monday, November 21, 2011

ATV Brake Bleeding How To

Most modern ATVs have hydraulic brakes that rarely need servicing, but once in a while I do have to work on them.  I have found that they can be stubborn to refill with fluid and bleed if the system has been opened up and all fluid drained out.  These photos show the brakes on a Yamaha Grizzly, but most machines work the same way.

After reassembling the system I connect a hand operated vacuum pump to the brake bleeder using a piece of clear tubing.

Fill up the reservoir with fluid, put a little vacuum on the bleeder, and slowly open the bleeder.

The vacuum will pull the brake fluid and any trapped air through the system.  The clear tubing will show the air bubbles escaping.  When the bubbles stop and there is only clean fluid coming out the brakes are properly bleed.

It is possible to bleed the brakes without the vacuum pump, using only the master cylinder to push the fluid through, but I have found that it can take a very long time.  The hand vacuum pump is an inexpensive tool that speeds up the process.

Thursday, November 10, 2011

ATV Wheel Bearing Replacement

Wheel bearing replacement is a common job on ATVs.  This machine is a Yamaha Grizzly, but most machines are put together the same way.

Once you remove the wheel the first step is to remove the large nut that holds the hub on the axle.  On Yamaha machines the nut is locked in place by a small portion bent into a groove on the shaft.  I use an old screwdriver that I have ground down to match the groove to pry this spot out.

The easiest way to remove this nut is with an impact wrench.  If you do not have an impact wrench you need to find some way to keep the hub from turning.  One way to do this is to put a pry bar between the wheel studs.  Be sure to protect the threads on the studs with a short piece of rubber hose if you are going to pry on them.

Once the hub is off the spindle must be removed from the vehicle.  The ball joints (red arrows) and the steering tie rod (green arrow) need to be disconnected.  These are held in place with a nut on the end of a tapered shaft.

Remove the nut and pry or pound the ball joint loose.  If you are going to pound on the threaded end use something soft like a lead hammer to avoid wrecking the threads.  The other tool pictured is a ball joint fork, it is simple pounded in between the parts and the wedge shape drives them apart.

When you have the spindle on the workbench remove the clip that holds the bearing in place.  This one has holes in the ends that make it easier to get out. 

If you look close at these clips you will note that one side has sharp edges and the other side has edges that are rounded over.  (The top clip is sharp side up, bottom clip is round side up, it is more obvious in person than it is in the photo.)  These edges are a result of the way that the clips are stamped out when they are made.  When installing clips like this you should always put the sharp edge facing the direction that the clip is being pushed towards.  The sharp edge makes it less likely to slip.  In the case of these wheel bearings the sharp edge goes up.

To remove the old the old bearing I use a large hammer and a piece of pipe to pound the bearing out from the back side.  I do quite a few of these wheel bearings so I have made up a jig to hold the hub when I pound on it.  Make sure you have something solid to pound on.  I have an old cast iron weight from a tractor (about 75 lbs) that I put on my workbench.  In my old shop in Minnesota I had a large anvil to pound on.  If you don't have an anvil you may want to put your work on the floor.

Before you in install the new bearing you must make sure that the inside of the hub is clean.  Make sure there is no crud at the bottom of the bore or in the groove around the top.  Scrape or wire brush it out.

Heating the hub will cause it to expand and allow the bearing to go in much easier.  I use an electric heat gun, but a torch will also work. 

When installing the new bearing you can only push or pound on the outer race (green arrow).  If you apply any force (especially pounding) to the inner race or seal (red arrow) you will damage the bearing.    If you heated the hub up enough the bearing will drop in with only a few minor taps.

On this job I used a hammer to pound out the old bearing and tap in the new one. It may seem a little crude, but with care it works fine.  A hydraulic press could also be use to remove and install the bearings.  It would give a little more control, but the rules about protecting the inner race still hold true.  You must only push on the outer race.  An old bearing that has had the outside diameter ground down slightly makes a good tool for this job.  It can be used to press the new bearing in place and insure that the force is applied evenly.

Once the new bearing is seated all the way into the bore, install the clip to hold it in place.  Now the hub is ready to go back on the vehicle. 

Monday, November 7, 2011

Tool Tip

I resently came across a rusted bolted with a stripped out head.

I decided to use a a new tool on it.  It looks like the opposite of an "easy out". 

The curved teeth on the inside dig right into the bolt head.  The set I have are made by Irwin and cost around $20.  Worked great.

Battery Cables

The main battery cables for outboard motors are a constant source of problems.  If the battery and cables are not secured in the boat properly they move around and the constant bending leads to a failure of the insulation where the cable enters the lug.  Once this insulation cracks the moisture gets into the wire and starts to corrode it.  As you can see in this photo, the end of this cable broke right off when I bent it.

To repair this cable I cut several inches off of the end to get back to a less corroded portion of the wire.  I then used a wire brush to clean the wire up in preperation for soldering.

I use a large punch with a rounded end to crimp the new ends on the cables.  You must use a large hammer and a solid surface to pound on.  A properly made crimp will produce enough pressure to bond the metal parts together (like a cold weld).  To do it properly requires a rather expensive tool with dies made specifically for each size fitting.  A hammer and punch comes close.

To ensure good electrical contact I solder the terminals after crimping them.  Remember to put some flux on the wire before you start.  It takes a lot of heat to make a good solder joint this size.  I use a propane torch for this.

To make a lasting connection you need to keep the moisture out.  I use liquid electrical tape to seal all the connections.  Simply brush it on and wait a few minutes for it to dry.

The last step is to put a few wraps of tape around each fitting.  This protects the seal underneath and also makes a simple strain relief to prevent the wire from bending right at the terminal.

Tuesday, November 1, 2011

Broken Shift Lever

The shift lever on an ATV takes a lot of abuse.  They are constantly being kicked and pushed around with your foot.  The most common problem with them is that they work loose and the small splines that connect them to the shift shaft wear out.  That did not happen to this machine, instead the lever simply broke off.

This photos shows me holding the lever in place where it is supposed to be.

This close up tells a little more of the story.  To remove the lever you take out the pinch bolt by the green arrow and the lever slides off the shaft.  It is important that the bolt is removed all the way, there is a groove in the shaft that the bolt passes through.   A few years ago someone was working on this machine and wanted to get the shift lever off for some reason.  They loosened the bolt, but did not remove it all the way, leaving the lever loose but still stuck.  They then got a large crow bar and preyed on the back side of the lever.  Eventually the small C clip that holds the shift shaft into the transmission failed and the whole shaft came loose.

After this happened they called me up to ask if I could fix the shift shaft that was now falling out of the transmission.  To fix it properly would require removing the engine from the machine and splitting the entire engine and transmission open to replace the C clip on the end of the shaft.  This would be a very long and expensive job. 

In order to save myself some time (and the customer a lot of money), I found an easier way.  The shaft was still able to shift the gears inside, but would simple fall out because there was no longer anything to hold it in place.  The red arrow points to my quick and easy solution.  I simply welded an "ear" unto the frame that keeps the shaft from sliding out.  It has worked fine for several years, and this new problem appears to  be unrelated.  This time the lever actually broke off at an original factory weld.

Fixing the lever this time is a rather simple welding job.  The only complication is the limited access to the welding area.  This photo shows one of my welding tricks.  Sometimes you can bend your welding rod to reach around obstructions.  In this case I used a "U" bend in the rod to allow me to weld on the back side of the lever where there is only a couple of inches of space.

Here is the completed job, ready for a few more years of being kicked around.