How to choose the correct oil for your dirt bike

Motorcycle specific oils are refined by a completely different process than regular motor oils

Gloria Cunningham rides a dirt bike up a mountain with a lake and more mountains in the background.

If the owner’s manual recommends 20w-50 for your 4-stroke then don't buy 10w-30 weight oil. The most common weight for dirt bikes is 10w-40. — Photo courtesy Gloria Cunningham

The lifeblood of any combustion engine is the oil which helps lubricate moving parts to reduce friction. But which oil is best for 2 and 4 strokes? And what oil should you be using in what part of the bike?

What oil should I be using in my 2 stroke motocross bike?

The older technology is a 2 stroke that has a simple system that needs two types of oil to survive. One being Dirt Bike Gearbox Oil which is used to lubricate your bottom end bearings, clutch, and transmission.

A decent motorcycle oil designed for wet clutches will be around 80w which is a number to quantify the viscosity of the oil. Avoid using cheap oils or oil made for cars as the viscosity will not be the same and this may damage a motocross bike’s high-performance engine.

For the top end of your two-stroke motor being the piston, rings and top end bearings a different type of 2 stroke oil is added to the fuel at a certain ratio to act as lubrication which is burnt up upon combustion. Typical fuel/oil ratios in two-stroke racing machines are from 20:1 to 50:1 and everything in between. 20 parts fuel to 1 part oil. = 20L of fuel to 1L of oil.

Always check your owner’s manual to see what the recommended ratio and brand of oil is for your particular bike as too much or too little oil in your fuel can lead to engine damage or seizure!

What oil should I be using in my 4 stroke motocross bike?

Most modern-day four-strokes on the market (apart from the CRF450 and CRF250) use the same motor oil to lubricate everything from the valves, cam, piston, crank, clutch and transmission. This “all in one” oil system forces the motor oil to lubricate more than twice the amount of moving parts as the traditional independent premix and gearbox oil of a two-stroke machine.

Four-stroke oil for racing motors has been engineered in a way to produce maximum power from a lightweight and simple engine casing. The engine has been streamlined so much so that a motocross engine uses just enough oil to get the job done and nothing more. On a racing machine it is crucial you have a routine maintenance schedule which is assisted by an hour meter to ensure your engine is protected. Four-stroke machines also have Dirt Bike Oil Filters which should be replaced whenever you change your oil.
If you struggle with making a mess while changing your bike oil, using a handy product called Racetech Oil Catcher can reduce the mess and make life easier!

What is the difference between a motorcycle and car oil?

Motorcycle specific oils are refined by a completely different process than regular motor oils. They are mixed with five times the amount of additives such as anti-wear, anti-scuff, and additives to withstand extreme pressure which a regular motor never reaches compared to your racing engine.

Regular motor oil usually has friction modifiers and emission reducers which reduce engine wear on your family car but simply don’t agree with the clutch of a performance engine.

Why do some bikes have separate oil compartments?

Separate oil: The advantages of separating the oil, as Honda does, is that the top-end is not contaminated by clutch debris or broken teeth. Also, the heat of the combustion side of the engine does not thin out the oil which is designed for your transmission and clutch. The oil in each compartment has different qualities and is designed specifically for each application.

The downside of having two smaller oil chambers is increasing the need for more frequent oil changes and even a small loss of oil can be disastrous when there is only a small supply of oil to begin with.

Shared oil: The benefits of using the same oil throughout the engine, like the RM-Z, KX-F, KTM, and YZ-F, is that the large supply is less likely to run low and reach critical levels. With the larger oil supply, overall engine temperatures are reduced and oil changes are not needed as often.

How do I choose the right oil for my dirt bike?

The simplest way to select the correct oil for your bike is to consult your owner’s manual. Inside it will tell you everything from the weight of the oil through to the quantity and also recommend which brands to use. It will also guide you to where the filling/draining points are, where the Dirt Bike Oil Covers are and how to check your individual bikes oil level.

If the owner’s manual recommends 20w-50 for your 4-stroke then don't buy 10w-30 weight oil. The most common weight for dirt bikes is 10w-40. Your owner's manual also explains what ratio to mix your oil and petrol for the 2-stroke engines out there. Following this and also tips on correctly jetting your bike will give you the best performance, fewer rebuilds, and less exhaust smoke.

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