Why Is My Dirt Bike Leaking Oil?

It’s happened already. You found that spot of oil on the ground, and it came from your dirt bike. What does that mean? 

Dirt Bike Oil Leak

A dirt bike leaking oil can come from many different areas. Some are problematic, but some are of little consequence. First, you have to find out where the leak is coming from. Once you see the source, the next two questions are why is it leaking and how do I fix it?

This article will answer all of those questions.

The most common areas that leak oil on a dirt bike are:

  • Shifter seal
  • Drain bolt gasket/o-ring
  • Breather hose
  • Crankcase gasket
  • Cylinder head
  • Forks
  • Exhaust (2 stroke)
  • Cracked Case

How Long Can You Ride With An Oil Leak?

It Really depends on how much oil is leaking and where. Does the engine case have a hole in it from hitting a rock? If oil is quickly draining out, you’re not going to get very far. This is why it’s smart to have quick steel in your trail pack. 

A little drip here and there of oil is not going to hurt as long as there is still enough oil in the engine. Always check your oil before going on a ride so you know what the level is.

If you know it’s a little low and you don’t notice a leak until halfway through your ride, you can be confident that it’s not using much oil by checking the level again and comparing it to when you started. 

Oil Leaking From Shifter Seal

The shifter lever is connected to the shift shift that comes out from the engine case. Most dirt bikes have a rubber oil seal around the shaft to keep the oil in the engine. 

Shift shaft case bore is cracked and leaking oil.

This rubber will get hard over time and lose some of its seal, causing a leak. Excessive wear from a lot of use or dirty oil can also ruin the shift shaft seal. 

Simply replacing the seal with a new one will fix your oil leak as long as the engine cases is not damaged. 

How To Fix Oil Dripping From Drain Bolt

The oil drain bolt gets used a lot, or at least it should because you change the engine oil often enough. The bolt should have a crush washer on it that seals the bolt to the engine case. 

An old or cracked washer will cause a slow leak. Replacing it with a new one will usually stop the oil from dripping down onto your floor. 

Another issue that’s more serious is that the engine case is cracked. Clean the cases if they are dirty and inspect for cracks or damage. 

A cracked case where the drain bolt is would either be caused by hitting something or over tightening the drain bolt. 

Why Is Oil Dripping From Breather Hose?

The crankcase breather hose is there to let out the excess of air that the engine pumps up. Too high of an oil level can cause oil to leak out the breather hose on your dirt bike. 

If you see oil coming out of this house or tube, simply check the oil level. If it’s too high, you can try draining some oil out to correct it.

Oil Leaking From Crankcase Gasket

This one may suck to realize. A little weepage is actually not that big of a deal, however. Paper gaskets get hard with age and may lose some of the seal.

About the only time that is a concern for a leak from the crankcase gasket is when there is physical damage to the case, or the gasket/case was incorrectly installed.

Cylinder Head Leaking Oil

This is a similar case to the crankcase gasket. A cylinder head leaking oil is usually from old and hard sealer for the cam tower. This may look ugly and dirty oil may cover a large portion of your cylinder over time.

As long as the oil level isn’t noticeably going down, there’s not much to worry about.

You can wipe off the excess oil, or leave it for “character”.

Forks Leaking Oil? Try This First!

Leaking forks is another frustrating problem. Maybe you just had them serviced. All it takes is some dirt packed into the seal or a small nick in the fork tube for a leak to start.

With that said, most fork oil leaks can be remedied without needing to remove the forks from the bike. All you need to do is clean the fork seals.

Here are the steps to cleaning your fork seals with a Seal Mate:

  • Remove the fork guard if it has one.
  • Use a pick or small screwdriver to pull the dust seal off (careful not to scratch the fork tube)
  • Take the Seal Mate and stick the “hook” end in the fork seal. 
  • Rotate it around the fork tube while pulling any dirt “out” from in between the seal and fork tube. 
  • Do this until it is clean, then re-install the fork parts and ride again. 
  • You may have to add a little bit of fork oil if a significant amount leaked out. 

If cleaning the fork seals didn’t fix the leak, then the seal is most likely torn and needs to be replaced. Clean and fix any Nick’s in the fork tube that might have caused this before putting everything back together. 

Bad Connection Causing Exhaust Oil Leak

An exhaust leak is caused by a poor mounting connection or a bad seal.

First, make sure all of the connections and mounting hardware is tight. 

Is It Bent?

If everything is tight, take a closer look to make sure the exhaust system is straight. All it takes is a bent mount from a tipover to tweak the exhaust out of alignment. 

Most exhaust systems can be straightened by a professional. This can be considerably cheaper than buying a new one, but you may lose some of the coating if it needs to be heated up. 

Leaking Seal/O-ring?

A bad seal will cause an exhaust leak. This can be caused by an old seal that got hard or installing a new or used seal incorrectly. 

Replacing the gasket or o-ring with a new part and properly installing it on a straight exhaust should give a good seal that won’t leak oil. 

Cracked My Case! Can It Be Repaired?

A cracked engine case is like a sucker punch to the gut. Putting a hole in your case while out in the middle of nowhere will ruin your day… unless you go prepared!

While it’s not a good permanent fix, using some quick steel to cover the hole should get you back to camp or home. 

Make sure to check the oil level before taking off again, because if it’s too low, you may end up seizing the engine due to lack of lubrication. 

How To Fix A Cracked Case On The Trail

Preparing the surface on and around the hole is the most important part. If it’s not clean and dry, the new material will not stick. 

In a perfect world, you would have sandpaper and rubbing alcohol wipes to rough up and clean the surface, but those items aren’t in everyone’s trail pack. 

Get creative and wipe it down as best you can. Stealing some gas from your buddy’s tank will do a good job of cleaning the area to prepare it. 

Whether you use JB weld or quick steel, just remember to follow the instructions for mixing it properly. 

Taking the time to do it right will significantly improve your chances of making it back. Otherwise you’ll end up doing it again or be stuck and have to tow your bike out.

The Bottom Line

If your dirt bike is leaking oil, check to see where it’s coming from and how much. Always check the oil level before riding. If the oil level is low every time because of the leak, then it’s time to repair it. 

Kelley Fager

Kelley started riding a Honda 50 at the age of 6 years old. The passion for dirt bikes started there and grown into a lifelong pastime of riding and learning how they work. Motocross Hideout is the result of sharing his past, present, and future knowledge and experience.

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