Learning 2

If you have been reading my posts your probably thinking that I haven't got anything done, which isn't exactly true. While I've made a disappointing amount of progress on solving my quads mysterious problem, this project hasn't been a true failure. My goal wasn't just to fix this quad, it was to learn about internal combustion motors, how they work, and how to service them. Throughout the course of this project I have learned a lot about motors, all the understanding I showed in previous posts was a direct result result of prior research. To demonstrated what I've learned I'll just explain in a very basic way, how internal combustion engines work.

Internal combustion engines use one or more pistons to turn a crankshaft. The piston harnesses the energy of expanding gasses in the combustion chamber, using them to to turn the crank shaft. The cylinder is a sleeve of sorts that the piston reciprocates inside of, there are several types of motors that are named based on the configuration of their cylinders.

These primitive drawings show common engine configurations. Despite the poor drawing, the cylinders, line of v motors are parallel to each, the v represts the angle the cylinders come out of the motor at.

The cylinders in most motors with three or more cylinder are bored from one piece of metal, called the engine block. The pistons,  cylinder, valves, cam shafts etc, are known as the top end, while the crank shaft, connecting rods, engine casings etc are known as the bottom end.

Two stroke or four stroke, what's the difference.
The stroke, or cycle refers to how many strokes the piston takes per one combustion.

Two stroke motors are the simpler of the two motors, there are only 2 piston strokes, and they usually require oil to be mixed with the fuel in order to lubricate the cylinder.
As the piston moves up it compresses the air fuel mixture in the cylinder, when the piston is at the top of its stroke the spark plug  ignites the mixture, forcing the piston down in a combustion stroke. As the piston moves down, it passes an exhaust port near the  middle of the cylinder, and exhaust gasses are let out. The piston continues moving down past an intake port at the bottom of the stroke, drawing air into the cylinder. The air is compressed, ignited and the the cycle continues. to give you a better understanding, here is a link to a YouTube video of a two stroke animation. http://motocrossactionmag.com/bike-tests/ktm-tests/everything-you-need-to-know-about-the-all-new-ktm-factory-edition-iv

This primitive diagram shows a cut away of a two stroke cylinder.

Four stroke motors are more complex than two strokes, have more moving parts, and are more difficult work on. Four strokes are able to lubricate there cylinders, eliminating the need to mix oil in the gas. there are 4 piston strokes in a four stroke. As the piston moves up it compresses the air fuel mixture in the cylinder (compression) when fully compressed the spark plug ignites the mixture, forcing the piston down (combustion). As the piston moves back up, an exhaust valve(s) open and the exhaust gasses are released (exhaust). The piston moves back down, and the intake valves open, allowing fresh air and fuel into the cylinder (intake). My Polaris is a four stroke. To give you a better idea, here is a link to a YouTube video of a four stroke animation. https://www.youtube.com/watch?v=2Yx32F1cncg

This primitive diagram shows a cut away of a four stroke cylinder.

Two strokes have twice as frequent combustion strokes, compared to four strokes. This allows the engine to rev higher, and produce significantly more power than a four stroke in the same displacement. Two strokes are cheaper to make, and easier to service. Two strokes are very inefficient, and burn more fuel than four strokes, as well as burning oil in the gas, which creates a whitish blue exhaust gasses that are very harmful for the environment. A two stroke also has a large bloated header called an expansion chamber, that gives the exhaust gas extra room before it flows to the exhaust Two strokes have a distinct tinging sound that some people love, and some people hate. Two strokes may be able to produce a lot of power, but the power is created in an unpredictable, (hard to control) way, with power violently peaking at high RPM. Because two strokes make more power in a smaller displacement than four strokes, they have a smaller displacement limit in motocross race classes. 125cc two stroke race with 250cc four strokes, and 250cc two strokes race with 450cc four strokes. Two strokes are less common than four strokes, and are usually only used in dirt bikes, snowmobiles and  small single cylinder utility tools such as chain saws,or weed trimmers.

Four strokes may have a less frequent combustion stroke, but they are far more efficient, producing more power, and significantly more torque at lower RPM. Four stroke create power in a much more linear way than two strokes, which makes the power easier to use and control. Because four stokes have less power strokes, however the power strokes harness the energy more efficiently, less power strokes means the motor burns considerably less fuel as well. Because four strokes don't burn oil, they're exhaust gasses are significantly less harmful to the environment. Because two strokes make more power in a smaller displacement than four strokes, they have a smaller displacement limit in motocross race classes. 125cc two stroke race with 250cc four strokes, and 250cc two strokes race with 450cc four strokes. Modern Four stroke motocross engines are extremely powerful, and have been dominating the smaller two strokes in racing. For example, a modern 125cc two stroke has about 33 horse power while a 250cc four stroke has about 38 horse power and significantly more torque. Four strokes are extremely common and are used in all cars and trucks. My Polaris is a four stroke, Polaris  chose to use a four stroke because it makes much more torque and power at low RPM than a two stroke. The low-end power and torque are much more useful in a heavier quad than in a light dirt bike.

This picture shows the intake valves (right) and exaust valves (left) on my quad.

In this vague exaggerated dyno graph the dotted line represents a 125 two stroke while the solid line represents a 250 four stroke. As you can see the four stroke makes more power at lower RPM, and consistently climbs to its max power. The two stroke makes much less power at low RPM, before it hits its (power band) at higher RPM where power rapidly increases. This rapid transition from low power to high power makes two strokes more difficult to control.

All motors get very hot while running, The heat is a product of the combustion process. Obviously igniting gasoline creates a great deal of heat, in fact up to 60-80 percent or more of the total energy a motor produces is thermal energy in the from of unwanted heat. This heat, if not dissipated, will cause parts of the motor to deform and break.

There are three ways a motor is cooled.
The most primitive way is air cooling. Air cooled motors simply have fins on the cylinder that increase the cylinders external surface area, allowing the colder outer air two cool the fins, and cylinder. Air cooled motors, can be very reliable, as there is no liquid cooling system to break. Usually only small motors are air cooled such as chain saws, or motorcycles. Air cooling is not as effective as the other options, as a result the motor usually cant be pushed as hard.

The most common way a multi-cylinder motor is cooled is liquid cooling. In a liquid cooled motor, water or coolant is circulated through channels in the cylinder by a water pump that is usually driven by the motor. The water absorbs the heat from the cylinder and is pumped to the radiator, which has hundreds of tiny fins on the outside, and many grooves on the outside. The large surface area of these fins cools the water in the same way that the fins on a air cooled motor cool the cylinder. Liquid cooling is far more effective, because liquid transfers heat much better, than air, and the circulating liquid allows for faster cooling. Essentially all performance motors use liquid cooling because it allows the motor to run harder for longer. All new cars and trucks use liquid cooling, because the motor is inside an enclosed engine bay where fresh cold outside air can not circulate to cool the cylinders of an air cooled motor, also air cooling only works  on motors with separated cylinders, while the cylinders in all new cars are in engine blocks.

The radiator in this picture is hard to see, its the large rectangle behind the shocks, and steering column.

Oil cooling is usually only found in performance motors. Unlike the first two cooling systems, oil cooling does not cool the cylinder. As a result oil cooling has to be paired with a cylinder cooling system, (pretty much always liquid cooling). Oil cooling cools the oil, using a device similar to a radiator, that the existing oil pump circulates the oil to. Cooled motor oil cools the bottom end of the motor, as well as all the parts it lubricates, There are two types of oil cooling, motor oil cooling, and transmission oil cooling. The motor oil mainly cools the bottom end of the motor, while the transmission fluid (oil) cools the gears in side a transmission. some industrial vehicles also have differential cooling, which is identical to transmission cooling.
 And in case you didn't know, the differential splits power between the pairs of wheels while turning, taking power away from the inner wheel to allowing the outer wheel to turn at a faster rate than the inner wheel, resulting in easier turning, and no loss of traction. My quad has a solid rear axle and no differential. This means that in order to turn, the inside back wheel must break free and lose traction. Because of this the only way to effectively turn is to slide/drift which is awesome.

A transmission or gear box allows multiple graduated gears to be selected, this allows the vehicle to put as much power or tourque to the wheels at a given speed as possible. The gears are graduated, the gears start off low, allowing the motor to turn the wheels at a rate more closer to the motor rate, this allows for much faster acceleration, however, the motor will reach max RPM very quickly, and at a low speed, at this poin you simply shift into the next slightly higher gear and the process repeats itself. Gear boxes are very complicated and I won't explain them. Manual car transmissions are shifted by your hand on a stick, that must be placed in the correct shift spot or gate to select a gear. Motorcycle and quad transmissions are operated by a toe actuated shift lever on the left side of the bike. Unlike car transmissions, bike transmissions are sequential meaning you simply bump the shift lever up to shift up, and down to shift down.

A clutch is another incredibly important part of almost all motorized creations. The clutch transfers power form the motor to the gear box, and can be disengaged to allow for shifting. Clutches are found in many pieces of machinery. The most basic type of clutch would be the type of clutch a weed wacker or chainsaw has. These clutches are centrifugal clutches. The clutch uses springs to keep itself disengaged at low RPM allowing the motor to turn without engaging the implement. At higher RPM the centrifugal force on the clutch increases, overpowering the springs and allowing it to engage two friction plates, sending power to the implement (spinning the weed wacker, or turning the chainsaw chain). The clutches in manual cars are very different, and are manually operated. Naturally the clutch is engaged, and the clutch pedal must be depressed to disengage the clutch (separating the two friction plates). Without neutral, or a clutch, no vehicle, could really start, or be drive-able, because the wheels would always spin with the motor, meaning you could never stop without the motor dying, and starting would require enough force to move the car. The clutches found on motorcycles, dirt bikes  and quads have multiple friction plates not just two. This is because the plates have to be much smaller, to fit in a small space on the side of the motor, a space where car sized friction plates could never fit. In order to make the clutch strong and prevent clutch slippage despite the small friction plates, multiple plates are used (my quad has 8 I think). the increased number of plates not only increases clutch friction, but makes the clutch significantly easier to disengage, which is very necessary consider you use a finger lever to disengage the clutch. To get a better understanding, heres a YouTube video of a clutch animation. https://www.youtube.com/watch?v=TcYsV063lk8