For this week’s Q & A I’m going to talk about why changing the engine’s oil is particularly important for high performance dirt bike engines. Dirt bikes and their engines must contend with all sorts of nasty elements including dirt, mud, water, and sand to name a few. The exposure to these elements, the fact that four-stroke dirt bike engines don’t carry a lot of oil, and their high state of tune all necessitate the need for more frequent oil changes than traditional automotive or motorcycle engines.
Oil is the blood that keeps your engine alive. It is one of the most important things to check and change regularly. Four-stroke dirt bikes either have a separate oil cavity for the engine or an oil cavity that the engine and transmission share. Both types have their advantages and disadvantages.
Engines with separate oil cavities, where the oil’s only job is to lubricate the engine’s internals, benefit from having a cleaner oil supply. The oil is not contaminated by aluminum particles wearing off the clutch and circulating through the engine. The downside to the separate cavity is that the amount of oil used to lubricate the engine is less than a joint cavity. Usually around 700cc of oil is all that the separate oil cavity will hold. This small amount of oil gets circulated around the engine repeatedly and it doesn’t take long for the oil to become dirty, break down, and require changing.
Engines with separate oil cavities, where the oil’s only job is to lubricate the engine’s internals, benefit from having a cleaner oil supply. The oil is not contaminated by aluminum particles wearing off the clutch and circulating through the engine. The downside to the separate cavity is that the amount of oil used to lubricate the engine is less than a joint cavity. Usually around 700cc of oil is all that the separate oil cavity will hold. This small amount of oil gets circulated around the engine repeatedly and it doesn’t take long for the oil to become dirty, break down, and require changing.
Example of a separate transmission oil cavity
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Example of separate engine oil cavity
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Engines with one common oil supply for the engine and transmission benefit from a larger capacity of oil to draw from. The downside here is that additional parts are being lubricated by the oil supply and more contaminants are mixing into the oil. The main source of oil contamination is aluminum particles wearing off the clutch as the clutch is used. These aluminum particles then must be filtered or else they will circulate through the entire engine within the oil. If too many contaminants enter the oil supply the oil will act more like sandpaper than a lubricant, causing the cylinder, piston, valve guides, bearings and many other parts to wear.
Example of a joint oil cavity
External contaminants primarily enter the engine’s oil supply from two sources. First, as a result of the combustion process, small amounts of carbon will sneak past the piston rings each combustion cycle and enter the engine’s oil supply. This is one of the main reasons the engine oil becomes darker and darker with use. The second source of contamination is through the air filter. A dirty or improperly installed air filter which allows dirt into the engine will quickly dirty the oil and add to the number of contaminants.
When it comes to engine oil, the safe bet is to change the oil frequently so that the engine and its internals are always bathing in fresh clean oil. This will prevent excessive wear of components and help the engine last longer. How often the oil will need to be changed is dependent on the type of riding you do, how good your air filter maintenance regiment is, and the conditions you ride in. The manufacturer's recommended service interval is always a good place to start. If you’re racing, consistently running the engine at high RPMs, or riding in dirty or dusty conditions the oil will become contaminated and deteriorate more quickly. This means the change interval should be increased. To give you some guidance, when racing I change my oil every three to five hours depending on track conditions.
Lastly, I want to dismiss one common myth you may be wondering about. The myth is that engine oil which is dark or black signifies that the engine oil necessitates changing. This isn’t necessarily true and going off color alone won’t give much indication about the condition of the oil. The only way to get a good idea of how used oil is would be to send a sample to an analysis service for a comprehensive breakdown of all the different elements in the oil. Most people don’t care to do this so they change the oil out well short of its useful life. Oil darkens as more and more contaminants are suspended in it which is actually a good thing! Problems arise when the oil is old and there are more contaminants than the oil can suspend. This is why changing the oil frequently is a safe bet, so that the number of contaminants in the oil never surpasses the number of contaminants that the oil can suspend.
I hope this brief write up on oil, its importance, and the different types of oil systems used on modern four-stroke dirt bike engines increases your appreciation for just how important the lifeblood of the engine is! I know changing oil is not fun or exciting, but it is an essential maintenance task. By performing this task your engine’s life will be seriously prolonged. Questions or comments are always welcome!
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When it comes to engine oil, the safe bet is to change the oil frequently so that the engine and its internals are always bathing in fresh clean oil. This will prevent excessive wear of components and help the engine last longer. How often the oil will need to be changed is dependent on the type of riding you do, how good your air filter maintenance regiment is, and the conditions you ride in. The manufacturer's recommended service interval is always a good place to start. If you’re racing, consistently running the engine at high RPMs, or riding in dirty or dusty conditions the oil will become contaminated and deteriorate more quickly. This means the change interval should be increased. To give you some guidance, when racing I change my oil every three to five hours depending on track conditions.
Lastly, I want to dismiss one common myth you may be wondering about. The myth is that engine oil which is dark or black signifies that the engine oil necessitates changing. This isn’t necessarily true and going off color alone won’t give much indication about the condition of the oil. The only way to get a good idea of how used oil is would be to send a sample to an analysis service for a comprehensive breakdown of all the different elements in the oil. Most people don’t care to do this so they change the oil out well short of its useful life. Oil darkens as more and more contaminants are suspended in it which is actually a good thing! Problems arise when the oil is old and there are more contaminants than the oil can suspend. This is why changing the oil frequently is a safe bet, so that the number of contaminants in the oil never surpasses the number of contaminants that the oil can suspend.
I hope this brief write up on oil, its importance, and the different types of oil systems used on modern four-stroke dirt bike engines increases your appreciation for just how important the lifeblood of the engine is! I know changing oil is not fun or exciting, but it is an essential maintenance task. By performing this task your engine’s life will be seriously prolonged. Questions or comments are always welcome!
Want more dirt bike maintenance tips and info? Click the button below to subscribe our eNewsletter and get our weekly posts sent right to your email inbox!
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