If you compare the engine, the power source of a motorcycle, to a human heart, the engine oil circulating inside the engine is the blood. The engine oil, which protects against rubbing and bumping metal parts on the internal engine and plays an important role in heat dissipation, must be changed regularly. Using the popular model the YAMAHA SR400 as an example, we will explain how to change oil from Part 1 to Part 3.
When draining the engine oil, first you must prepare an oil drain pan before you begin your work.
1. There are 2 methods of engine oil storage, the Wet Sump and the Dry Sump.
There are several criteria for classifying oil, such as mineral oil, chemical synthetic oil, and viscosity indicating stickiness, but even any high-performance oil, the performance decreases, depending on travel distance and using term increases.
Oil changes are required regularly because deteriorated engine oil reduces the protection of internal parts and causes engine wear out by the reduced viscosity of the oil film.
By the way, do you know that there are 2 methods "Wet Sump" and "Dry Sump" to manage the lubricating engine oil?
A wet sump is a type in which all the oil is put in the crankcase, whereas a dry sump is equipped with an oil tank in a separate location from the engine.
Both have advantages but most of current engines use Wet Sump. The YAMAHA SR400, which is keeping its popularity high without changing its basic design since launched in 1978, has been adopted the Dry Sump.
A feature of this engine uses the down tube of the frame as an oil tank separate from the engine. Since the drain bolts are located at the lower part of the crankcase and the lower part of the oil tank, 2 oil drain bolts must be removed when oil change.
・Engine oil has important roles such as lubrication, cooling, and maintaining compression pressure.
・Performance decreases due to the use of any oil.
・There are 2 methods “Wet Sump” and “Dry Sump” to manage the lubricating engine oil.
2. When draining oil, remove the drain bolt after warming up the engine.
Oil drain bolts of SR400 are located at the bottom of the crankcase and in the center of the main stand pivot. It is good to loosen the drain bolt while the main stand is standing because it interferes with the stand when using the tool.
When the engine oil temperature is warm, not when it is cool, it will flow more smoothly and can be drained smoothly.
However, the oil temperature may reach nearly 100 degrees after the engine stops. It requires appropriate cooling time due to risk of burns by hot engine parts.
The oil drain bolt on the engine body of the YAMAHA SR400 is installed to the bottom of the crankcase facing backwards. It is difficult to be checked without completely lying down on the ground because it is a place between the left and right pivot of the main stand.
Some people may not like to lie down on the ground, but it is important to work with a visual inspection, because if you try to rotate the drain bolt by groping or in half-way posture, there is a risk to get injured by being come off the tool or break the head of drain bolt. In addition, using a box end wrench or socket tool instead of a spanner or adjustable angle wrench is recommended.
Spanner and adjustable angle wrench can be used at an angle to the bolt, but there is also a disadvantage which is broken and come off the bolt head in case of using it to large tightening torque bolt.
The box end wrench and socket tool can firmly convey turning force because they touch 6-point of the bolt.
▲ If you try to loosen the 17mm drain bolt at the bottom of the engine with a spanner or adjustable angle wrench, there is a risk to slip from the bolt, so using a box end wrench or socket tools is recommended.
・Drain the oil while the oil temperature is warm in order to drain oil smoothly.
・Work in a visible state rather than removing the drain bolt by groping.
・Use a box end wrench or socket tool to prevent the bolt head to break, not a spanner or adjustable angle wrench.
3. Oil Drain Plug Gasket must be replaced.
Crash type gasket is crushed by tightening bolts to ensure a tight seal. Therefore, it requires replacement every time because it will flatten as shown on the left gasket once it tightened.
Crash type gasket is made of thin metal in complex shapes. It will be crushed to prevent oil leakage by being sandwiched between the bolt and the engine body.
When removing the drain bolt, there should be a gasket under the bolt head. Make sure to collect the gasket if it sticks to the crankcase and falls into the waste oil container. Unlike ordinary washers, the drain bolt gasket is an important part that closes a small gap between the bolt and the crankcase to prevent oil leakage.
Engine oil will spill out from the gap between the bolt and case mating surfaces if you do not notice that it has fallen into the waste oil container and restore the drain bolt without a gasket.
In addition, the gasket crushes itself and deforms to close a small gap if the drain bolt is tightened. Therefore, it is not recommended to reuse a gasket that is already crushed.
In particular, a crush type gasket that also uses SR should be replaced every time because it is crushed and stuck by the tightening torque of the bolt.
・The drain bolt gasket should be changed to new one.
・The drain gasket is an important part that prevents oil leakage by being crushed.
・Oil may leak if gasket is not used.
4. Remove the oil from the oil tank after wearing an anti-dirt apron.
The SR400 uses the down tube of the frame as an oil tank. If you remove the lower drain bolt of the oil tank, the oil will be drained forward. By putting the corrugated cardboard under the front fender, the tires and fenders can be kept clean.
When the oil in the tank is few, the force is lost, and it flows down along the frame. If you put a sticky tape on it's route, the frame and engine will not get dirty.
After draining the oil from the crankcase, drain the oil in the tank from the drain bolt at the bottom of the down tube. This bolt is easy to turn because it faces the front of the motorcycle, but if you remove it without thinking anything, the oil will jump out toward the front tire, and it will be very troublesome to clean up. Therefore, before removing the bolt, let's place a plate under the front fender to fend off the oil that jumps out.
If under the plate is put in a waste oil container, the oil flowing out of the oil tank can be collected without hitting the front wheels or polluting the surroundings. In addition, when the amount of oil discharged from the tank decreases, it will flow through the frame, so it is possible to remove the oil without contaminating the frame or the engine by sticking a piece of adhesive tape under the discharge port.
The oil tank drain bolt also has a gasket, but this is a copper plate type, not a crash type. The copper gasket is softer than iron oil tank and iron drain bolt, although not as much as the crash type, they are crushed to fill a small gap.
If there is an obvious difference in level on the surface of the gasket, it can be replaced, but it is not possible to check it without removing the drain bolt, so it is better to prepare it in advance when changing the oil.
The drain bolt gasket in the oil tank is a piece of copper. It does not crush as the shape changes like a crash type, but it is softer than an iron washer, so it deforms and seals are secured. Therefore, this gasket also still needs replacement.
・Note that oil may come out vigorously.
・Cover up the route where the oil jumps out so that the vehicle will not get dirty.
・For Dry Sump models, be sure to replace the drain bolt gasket of the oil tank.
Check the location and number of drain bolts in advance, and prepare a gasket before draining the oil.
Oil change is one of the basic items of motorcycle maintenance. However, if you start without any plan, it is also a thing to panic in the lack of preparation. By knowing the position of the drain bolts and how to flow the oil in advance, you will be able to do smart work without onerous cleaning.
The SR which is loved by many riders is a dry-sump model. For the owner who wants to change the oil by themselves, work smarter with advance preparation.
・Pre-training and preparation for the oil change is also important.
・If you know the position of the drain bolt and how to flow oil, you can work smartly without getting dirty.
・Gaskets also must be changed when oil change.