My Quad's Motor

My quad's motor is a 450cc single cylinder liquid cooled four stroke, with 4 valves, and two overhead  cams. The 450cc, refers to the displacement, which is the volume of space in the cylinder when the piston is at the bottom of its stroke. 450cc is the same as 450 millilitres or 0.450 litres. To help show the different parts of my motor I have drawn right side and left side diagrams.

The Parts that are not side specific, such as the intake, system, exhaust system, and cooling system are not showed in the left side diagram because they are showed in the right side.

Learning

This post will explain some of the things I have learned in this project.

the spark plug ignites the compressed air fuel mixture in a cylinder. It threads into the top of the cylinder, and uses a powerful electric spark, arking through the small gap at the tip of the plug to initiate combustion. Diesel motors do not have spark plugs,this is because the diesel air mixture in a diesel engine auto-combusts under the higher compression in the cylinders. Different spark plugs have different heat ratings that indicate how intense of a spark it can allow. The more intense the spark, the better the air fuel mixture will burn, resulting in a smoother more powerful motor. Running to hot of a spark can potentially damage the ignition system. the heat rating of my spark plug according to the owners manual is 9h.

The carburetor, in the simplest of terms, provides the motor with the correct mixture of air and gas. I decided not to take it apart and clean it, because the carb is fairly complicated, especially with the electric throttle position sensor. Instead I poured a healthy amount of sea-foam engine cleaner into the gas. Sea Foam can help clean the carburetor and motor when burned in the gas. I also learned that it is  important to run octane boosted premium gas in motocross engines, to keep the motor clean, and to get optimal performance.

My quads carburetor is a 38 millimeter (inner diameter)  of . The carburetor is located in between the air box (right) and cylinder (left) as the motor draws in air from the air box during the intake stroke, the air is pulled through the carb where it is mixed with a small amount of fuel. The black hose connecting to the carb is the fuel line from the gas tank, it fills the float bowl (bottom of carburetor) with gas. The gas in the float bowl pushes a float, which allows gas up through several needles, there are several needles or jets, the 2 important ones are the idle jet, and the main (pilot)jet. The idle jet always allows squirts up a small amount of gas, regardless of throttle position allowing the motor to idle. the main jet allows more fuel into the air stream depending on the throttle valve position, ie you twist the throttle, and it allows more gas into the cylinder. The throttle also opens a large valve in the carburetor that controls air flow, the more throttle input, the wider the valve opens and the more fuel and air is drawn into the cylinder.

The top photo is a view of the throttle valve, the slight opening at the bottom is always open, it allows a small amount of air for the motor while its idling. 

 The air and fuel mixture does not need to be forced into the motor, the natural vacuum pressure caused by the piston going down draws the mixture through the intake valves with sufficient force. A A turbo charged or super charged motor forces more air into the cylinder than would naturally be drawn in under vacuum pressure. great deal of force  in and into the air flowing through the  carburetor. The orange hoses are overflow hoses, that allow excess gas to drain from the carburetor.

Goals

I have several different goals for this project. My primary goal is to restore the beat up sport quad I purchased back to a healthy operating condition. This will include  fixing a mysterious, and debilitating, motor issue, repairing plastics, changing fluids, changing filters, and probably fixing new problems I discover while fixing the old ones. I hope that by the end of this project I will be able to rip on  this quad with my friends, without having to worry about any problems.

My second goal is to learn as much as possible about the function and mechanics of the internal combustion motor, as well as maintenance, and servicing information. I believe that it is important to learn such things, because almost every adult uses at least 1 type of internal combustion motor on a near daily basis ( in the form of an automobile), and every motor requires semi frequent basis. By knowing how a motor workings and how to properly maintain and service it, you can not only save money by not having to take your motor to a shop for basic maintenance, you can prevent major problems by recognizing signs of a problem before it gets serious. I think that learning about motors will make my life easier in the future, and probably save me time and money.

My third goal is to learn because its fun. The interactions of moving parts of machines, motorized or not has always fascinated me, and I always want to know how they work. It never fails to amaze me how intelligently designed most mechanical devises, are I sometimes wish I could create such things. When I look at how a combustion engine works, I see a type of mechanical beauty. God has instilled upon man  intelligence, and resources. He has given us both the mental, and  physical resources necessary to create complex, and amazing things. I believe this project follows the religious through line of  beauty creating, even though at fist glance, a greasy, smelly machine may seem anything but beautiful. I believe we can honor God in our work, using our christian values in the decisions we make, and the tasks we do.

The Ignition System.

The ignition system consists of a series of components that create, and time the electric spark used to ignite the gas and air mixture in the cylinder during combustion. I knew that the only ignition system was to blame, and not the bikes entire electrical system because all other electrical functions continued to work after the bike losses spark. Electrical problem can be notoriously hard to diagnose and fix, which concerns me. The ignition system on most dirt bikes and sport quads consists of a stator coil, ignition coil, cdi box, and voltage regulator and kill switch.

sometimes a faulty kill switch can cause such problems however, the rest of the electric components functioned flawlessly, when spark was lost. if the kill switch was the problem, the bike would essentially just turn off, and nothing would work. 

My next suspicion was the stator coil, I had been talking with a Polaris mechanic and he said the problem might be the stator coil. the stator coil is a device mounted next to the flywheel, its turned by the motor, generating electricity for the spark, and charging the battery. On primitive motors the stator coil actually times the spark. Apparently the stator coil can crack over time, and still function properly when cold, however it will expand, and fail to generate electricity when hot. I was fairly confident that the stator coil was the problem, but then I learned something. Unlike kickstart quads and dirt bikes that don't have a battery, electric start machines use electricity  from the battery, not the stator to generate spark. This means that even if the stator failed, the bike would run until the battery died. However on my Polaris the battery is still fully charged when the machine dies.

Another potential culprit could be the CDI (capacitive discharge ignition) box. The CDI box is essentially the brain of the machine. It times the spark, determining exatly when the spark is created, CDI boxes stores electrical charge, before discharging it to the ignition coil, this causes the spark to be much more powerful. Sometimes when a CDI box becomes old it malfunctions, resulting in spark not reaching the spark plug.

The ignition coil is another potential part at fault. the ignition coil converts the 12 volts charge from the CDI box to a short powerful spark, peaking at up to 10,000 volts. The spark has to be extremely powerful because its very difficult for an electrical charge to ark across the spark plug gap while under the extreme heat and pressure of the cylinder.

 

Another part that could be causing the problem would be the wiring harness. The wiring harness is a bundle of wires from, every electrical component. The wiring harness contains all the wires keeping them compact and organized. The wiring harness on the Polaris is in tough shape, and if the insulation on a wire from the ignition was worn out, the wire could short on the frame, preventing spark.

Trouble Shooting

As I mentioned in a previous post my polaris has an issue where the engine dies after about 10 minutes of run time. I learned that this can be caused by a lack of one or more of three main things. Any gasoline motor stops running if it fails to receive gas, air, or spark.

My first move was to see if it was getting gas, I theorized that perhaps the fuel tank wasn't venting properly, which would result in fuel being unable to reach the carburetor. However after a few minutes of running the motor with the gas cap open, it still died. This ruled out a gas tank venting problem, however it still could be caused by a partially clogged fuel filter restricting the flow of gas to the carburetor. Unfortunately after cleaning the fuel filter with compressed air, the motor would still die.

 My next action was to check the air filter, (if not enough air gets though the filter the motor will run rich, and die) but it seemed ok, and the motor still died when it was removed. Both of these tests showed that the problem was either in the carburetor, or was an electrical ignition malfunction preventing spark.


Testing whether the motor is receiving spark is easy, you simply remove the spark plug and hold it against a metal part, while turning over the motor. If you see a strong blue ark come from the plug, all is usually good, if you don't, there's no spark. Obviously the motor receives spark initially, otherwise the motor would never start, I wanted to see if the the engine was dying once hot because of a lack of spark. I ran the motor until it died, pulled the plug, and sure enough it didn't spark. So the problem was electrical. The series of components  that create and time the spark are called the ignition system, and one or more of these parts was failing after a few minutes of run time.

If the spark is weak when outside the cylinder, it may actually  be unable to spark at all, under the extreme pressure of a cylinder.

Oil Change

My next step was to do a routine oil change. Its important to change the oil frequently on motocross motors, and the manual recommends changing the oil as frequently as every 10 hours. While the oil change is fairly basic, its still more difficult than changing the oil in most cars. The Polaris Outlaw 450 mxr uses the same oil for the motor and transmission, and the oil system contains 2 oil filters, as well as two oil screens.

Both of the motor's oil filters must be replaced every oil change, as you can see there is a short and long filter. The oil screens on the other hand can be reused.

The first step of the oil change is to remove the plastic guard that protects the underside of the ATV. The second step is to  remove the fill plug, and then the drain plug to drain the oil completely. After cleaning the fillings off the magnetic drain plug and reinstalling it you can move on to oil screens. The long oil screen is located just beneath the shift lever, and the short screen is underneath the motor, both screens must be removed and cleaned with compressed air, before reinstalling. The long filter is quite difficult to reinstall due to its size and location. Next are the filters, the filters are both located in housings on the left side of the motor.

The filters can easily be removed, however there was some old oil in the filter housing that would drain, installing the new filter is fairly simple, but a little bit of a mess.The filters should be filled with oil before installation, and naturally oil gets everywhere when you try to install them. When the oil filters are in you simply add 1.2 liters of the correct oil.

To make sure oil levels are correct and the motor and gear box have a sufficient amount of protection, the motor must be run for a few minutes to distribute the oil. There is a sight glass beside the rear brake pedal on the right side of the bike that can be used to view oil levels, when the level is about 1/3 cold or 2/3 warm, it is at the correct level.

Its important to check the oil level frequently, a decreasing level indicates, a leak or that the motor is burning oil, and an increasing level indicates that water or gas has contaminated the oil. Both of these scenarios can lead to damaged if not addressed properly.

My first step toward fixing theses newfound problems was to print out the 200 page owners manual. I learned that while the manual does provide some useful information, it also has a lot of useless, information and unnecessary safety recommendations.
Its important to note that my budget, for this project is small, I'm  trying to save money, and avoid purchasing costly parts, if they aren't  absolutely necessary.
The first act of maintenance was topping off, the radiator with some Honda ATV coolant. I then went about fixing the badly cracked rear plastics. If there's one thing I learned while fixing the plastics, it's that zip ties are your friend! They are easy to use inexpensive and surprisingly effective! I drilled holes in the rear fenders and used small red zip-ties to stitch them back together, zip ties were also used to secure the plastics, and fuel tank to the frame, In places where fasteners were missing.