Why Is My Dirt Bike Burning Oil?

Is your 4 stroke dirt bike burning oil? Are you tired of having to add oil every ride? Worried there might be more problems?

This article will cover everything you need to know about a dirt bike burning oil, whether it’s a major problem, and how to fix it.

Do Dirt Bikes Burn Oil?

All dirt bikes burn at least some amount of oil, whether it’s 2 stroke or 4 stroke. Different oil is burned in different engines though.

Symptoms of A Dirt Bike Engine Burning Oil

The most common signs that your dirt bike is burning oil are: smoking out the exhaust, high oil consumption, or a fouled spark plug.

Causes of An Engine/Motor Burning Oil

There’s a variety of problems that can cause your engine to burn oil. Almost all of them are engine related.

The most common causes of a dirt bike burning oil are:

• Using a gas and oil mixture
• Oil that’s been used for too long
• Gas diluted oil
• Worn piston rings
• Piston/rings scored
• Top-end not properly broken-in
• Leaking valve seal
• Oil overfilled

Can You Fix An Engine That Burns Oil?

Any engine that burns oil can be fixed. You just have to fix or replace the parts that are causing the problem. It may cost you nothing, but it may be hundreds of dollars if the engine needs to be rebuilt. 

Do 4 Strokes Burn Oil?

4 stroke dirt bikes burn a small amount of engine oil. The engine has to have certain tolerances to be able to run and be reliable.

The piston to cylinder clearance and piston ring end gap are the main clearances that allow some engine oil to burn.

Why Does Oil Get Burned Up?

There has to be a gap between the piston and cylinder. As the piston warms up it expands. If there’s no gap (clearance) then the piston will grow too big for the cylinder and seize because of too much friction.

Same goes for the piston ring. There’s a small gap on the ends of the rings for them to heat up and expand.

Since the engine oil is coated on the cylinder wall of a 4 stroke to reduce friction and heat, there’s a small amount of oil that will escape through these gaps. This oil will get burned up in the combustion chamber and go out the exhaust with the air and fuel mixture that was ignited.

2 Strokes Definitely Burn Oil

Part of running a 2 stroke engine is that it requires a mixture of oil and gas. This is either pre-mixed or oil-injected through a mechanical or electronically controlled system.

Either way, oil is and should be getting burned through your 2 stroke engine.

Engine oil does not reach the top-end in a 2 stroke as it does in a 4 stroke engine. The only other oil is in the transmission. If your 2 stroke dirt bike is burning transmission oil/fluid then you have bigger problems that need to be addressed.

4 Stroke Dirt Bike Smoking

As mentioned previously, a properly running 4 stroke does burn a small amount of oil, but it’s so small that you won’t notice the effects. That is, unless, it’s burning more than it should.

As an engine wears out, the clearances (gaps) will get bigger. Bigger gaps means more oil can get by and out the exhaust. This will show up as white or blue smoke coming out the exhaust.

Valve Seal Failure

Valve seals wear out and lose their sealing capability over time. A typical sign of a bad valve seal is if your dirt bike smokes when cold, but it eventually goes away after the engine warms up. This is because oil is leaking past the seal into the combustion chamber and then getting burned off. It will be an “oil-burning” smoke that has a distinct smell.

Simply replacing the seal should fix this problem, but I recommend inspecting the top-end while you have it apart. Things such as valve clearance, inspecting the cam(s) for wear, and the cylinder if you take the head off.

Using Oil For Too Long

Oil breaks down over time being used in an engine. As it breaks down, the oil essentially gets thinner. The thinner it gets the more easily it will seep past the engine clearances, such as the piston and ring gaps. 

Having enough oil in your dirt bike is the most important thing to keep it running reliably. Keeping clean oil in it is the second most important thing to remember. 

This doesn't mean you need to change it every ride, but you should drain and replace it when it gets dirty. Black oil is dirty oil. 

Gas Diluted Oil

Although it's not as common, gas that gets I to the oil can dilute it and cause it to leak into the combustion chamber to get burned away into smoke. 

It's similar to the overused oil, whereas the gas thins out the oil. 

Gas can get into the oil when you have a dirty carb float needle. It will stick open and cause gas to flood the engine. 

Cleaning the carb and possibly replacing the float needle is needed in this case. Cleaning the seat with a q-tip may be necessary. 

Keep the gas fresh and run non-ethanol fuel if possible. 

Top-end Not Properly Broken In

Breaking in engines isn't as important as it used to be decades ago, but it can still cause performance issues if you do it wrong. 

If your dirt bike has a cast iron cylinder sleeve, top-end break-in is even more critical than with a nikasil plated cylinder. 

Breaking it in too slowly will not properly deal the piston and ring(s). This will result in less compression, less power, and a higher oil consumption. 

Oil Overfilled

Last, but not least, did you overfill the engine oil? Having too much oil in the crankcases can result in the excess oil getting sucked through the vent hose to the air box. Once it reaches the air box, it will get sucked through the carb and burned off in the engine.

If you overfilled the engine with oil, either drain some out or take a vacuum hose and syringe to suck it out from the oil fill hole.

Things To Remember About Oil Burning & Smoke:

• Always check oil level before riding to help prevent a major engine failure
• Keep your eyes open and nose smelling for oil-burning smoke from your dirt bike
• 2 Strokes naturally smoke, but it should lessen as the engine warms up
• Burning oil has a distinct smell. Check the oil level if you start smelling it
• Some causes of oil burning are more serious than others
• When rebuilding the top end, remember to do it right the first time or you’ll have to fix it again sooner rather than later

How to prevent a catastrophic engine failure

If you've ever had your bike break down in the middle of nowhere, then you know what a pain that is to deal with... I want to show you the simple steps I've learned to help prevent this from ever happening. I made a 3 step guide that you can download for free. Click here to learn more.