10 Steps To Break In A Dirt Bike Engine (2 Stroke & 4 Stroke)

There are only two scenarios when you would need to break in a dirt bike engine. Either you’ve bought a brand new bike that has never been ridden. Or you’ve just done a complete engine rebuild. In either case, breaking in the engine is extremely important. There is a wrong way and a right way to do it.

There are tons of different “experts opinions” when it comes to breaking in a dirt bike engine. The problem is those opinions were most likely created back in the late ’90s where dirt bike engines operated very differently from how they work today. For example, check out this article I wrote about how motorcycle chains have evolved.

Disclaimer: The following are the steps I personally use when breaking in my dirt bikes. I am not responsible for any damage or accident that result from your own actions.

Do You Need To Break In A New Dirt Bike Engine?

The short answer is yes. Every new motorcycle engine should be broken in following the correct technique. Break-in procedures will differ across models and bike categories. For example, Harley Davidson suggests a conservative break-in process for the first 500 miles of riding. This differs from the optimal dirt bike engine break-in procedure.

The good news, however, is that you can follow the exact same procedure to break in a brand new dirt bike engine and an engine that has been rebuilt. The same procedure can also be used regardless of the engine size – 80cc, 125cc, 250cc, 450cc, and up!

Why Do You Need To Break In A Dirt Bike Engine?

Breaking in a dirt bike engine is important for the longevity and durability of the engine. An engine that has not been broken will not run at optimal performance levels and could have more faults (and less power) than an engine that has been properly broken in. The purpose of breaking in an engine is to allow the piston and rings to seat.

Dirt Bike Engine Break-In Process

I advise making sure that all liquids and involved parts are either thoroughly cleaned, or brand new. Check that the carb is clean, the fuel tank has been flushed clean and a fresh fuel/oil mix is used. The air box and air filter should also be dirt-free.

There are a few factors to think about before you even start your dirt bike. WARM-UP your dirt bike engine correctly. This step is vital. If you ride in cold weather, please read our guide on cold starting your dirt bike as well. Warming up your bike properly is not as simple as flipping the choke and fuel, cranking the starting, and letting it idle for 10 minutes. In fact – that is exactly what not to do. Note that the warm-up procedure differs for 2 stroke and 4 stroke dirt bikes.

Most people will tell you to break in your engine following a heat cycle process. I will tell you the same. Follow these steps to break in your engine and your dirt bike will serve you well for many rides to come.

1. If you have just rebuilt your engine you might have replaced other components like the carburetor, exhaust system, air cleaner and filter, compression settings, coolant, oil, etc. Any of these changes will affect how rich or lean your bike is running. Running too rich or too lean will damage the engine. Make sure to check the air/fuel mixture on the ECU and O2 sensor (fuel injected bikes) or use an Exhaust Gas Temperature gauge. Even with both of these methods, it’s recommended to check your spark plugs for signs that the air/fuel mixture is right/wrong.
   
   
2. While not necessary – in an ideal scenario, your engine would have air blowing over it to simulate what would be happening if you were actually riding. You can do this by positioning a fan head-on in front of your bike. You’re ready to start your bike. Give the bike a shake ensuring the oil and gas are mixed. Flip the gas and choke (if you have one). Make sure you’re in neutral gear. With very little throttle, kick the bike into life. Let it idle for about 60s seconds with the choke up then drop the choke and keep the engine revving at just above idle. Open the throttle about halfway every couple of seconds to let the revs climb and drop back down to just above idle. This climbing and dropping of RPM allow the piston and rings to settle in. Pay careful attention the how much heat the engine is generating. If your bike is air-cooled, you will be able to feel the heat building on the engine and exhaust. Once it becomes almost too hot to touch, turn the bike off. If your bike is water-cooled, monitor the temperature of the engine coolant. When the temperature gauge starts rising, turn the bike off. Congratulations! You’ve just completed your first heat cycle which should take less than 10 minutes.
   
   
3. Allow the engine to cool down, but not get completely cold. It should still feel a little bit warm to the touch. Repeat step 2 above – this time you want the engine to get a bit hotter than the previous heat cycle. Carefully listen to the RPMs and keep the engine running above idle by consecutively opening and closing the throttle just as you did in step 2, allowing the revs to climb just a little bit higher. Once the engine is too hot to touch (about 10 minutes), turn off the bike and let it cool
   
   
4. Give the engine time to cool down. This can take anywhere from 10-30 minutes. When it is just slightly warm to the touch, it’s ready for the next heat cycle. Repeat the process again, this time revving higher than you did in step 3. Do not hold the throttle open. Make sure you are only opening slightly more than in previous rounds and let it close. Once the revs drop down to just above idle, open the throttle and let it close again. Repeat the process for another 10 minutes.
   
   
5. You’ve now completed three heat cycles and it’s time to let your engine cool down completely.
   
   
6. Check for any liquid that may have leaked out. Only once your engine is completely cold, remove the spark plug and inspect the color to determine if the bike is running too rich or too lean. You should also inspect the cylinder head nuts as they can loosen during this process. Tighten them back to manufacturer instruction while being extra careful not to over tighten them.
   
   
7. Now that you have completed the stationary break-in process, it’s time to get your bike moving. Since your engine should now be completely cold, start the bike following my warm-up procedure in the link above. This initial ride should be for no longer than 10 minutes. Ride for between 5-10 minutes while varying the rev range up to about 50% throttle. The best way to do this is around a track or on a curvy road as this will help to keep the revs climbing up and dropping back down. Don’t be afraid to open the throttle. Riding at a low revving range (a.k.a lugging) is actually bad for the engine as it places a lot of strain on the motor. Turn off the bike after 5-10 minutes of riding and allow the engine to cool down until you can touch it. This usually takes anywhere from 10-30 minutes.
   
   
8. Repeat step 8, but this time you want to ride for slightly longer and get the revs up slightly higher. Aim for 10 minutes riding, opening the throttle up to about 60%. Let the engine cool down.
   
   
9. For your final break-in run, repeat the previous step but ride for 15 minutes, reaching about 70% throttle.
   
   
10. Allow your engine to get completely cold. Inspect the bike for any leaking lubricants, oils, or coolants. It’s worth pulling out the spark plug to check the air/fuel mix. Lastly check the cylinder head nuts. As mentioned, it is normal for these to loosen over time, just don’t over tighten them.

You have now broken in your dirt bike engine. All the components should be sitting snug and both you and your new engine are probably craving a good ride. So go out and ride! It’s advisable to avoid overheating on the first ride so it’s probably a good idea if you can avoid gnarly technical terrain or ultra-thick sand until your second or third big ride.

Top Break-In Tips

Breaking In A 2 Stroke vs 4 Stroke Engine

When breaking in a 4 stroke dirt bike it’s important to make sure that the valve train or top end is getting oil. Read your OEM owners manual which will guide you through this process for your specific bike model

The break-in procedure for a 2 stroke and 4 stroke dirt bike is pretty much identical. The only difference is that when you are replacing all the fluids, a 2 stroke needs a new fuel/oil mixture and a 4 stroke only requires new fuel. 4 stroke engines also need to have the piston rings seat. If they do not seat properly, the bike will smoke excessively.

To break in a 4 stroke dirt bike engine, use petroleum and not synthetic oil. I recommended Shell Rotella T4 15W-40. Once the break-in is complete, I recommend Motul 4T 10W-40 Synthetic Oil.