You just bought a brand, spanking new dirt bike.
It's clean, shiny and not a scratch or dent on it. It's perfect. You may even think perhaps its best as a show bike. Why mess it up? That'll pass soon enough and once the urge to ride takes over you'll want to get it dirty as quickly as possible.
But first things first. You can't just gas up and ride it like James Stewart on the last lap of a Supercross race. Or can you?
Many, many opinions exist on how to properly break in a dirt bike engine. Lots of methods get passed down through family tradition and if your dad showed you how he broke in a dirt bike engine, you'll follow his advice, and your kids, your advice.
Today's dirt bike engines are vastly different than engines from the 1970s. But two facts remain, it's still an engine with lots of tiny parts moving at high rates of speed. Secondly, you want it to last a long time. Breaking in an engine helps seal the pistons rings into the cylinder surface. Without a proper seal you end up with engine issues, sometimes sooner rather than later, but almost always inevitably later.
This shiny new 4-stroke engine needs to be properly broken-in
The old school way of thinking is heat cycles. The "three heat cycle" seems to be most popular. Turn the engine on, let it idle for 10 minutes, give it a couple of revs, then shut it down. Cool off completely. Repeat. Repeat again.
Variations of the heat cycle differ widely. Some call for idle only for all three heat cycles. Others suggest the best engine break-in is to idle the first cycle, then ride your bike at low speeds for the second cycle and then ride like normal for the third cycle. Other owners add additional heat cycles at various throttles.
Another idea making its way into chat rooms and discussion forums is the complete opposite of the "ease into it" routine. In short, you run the engine hard the first time out, which according to the advocate of the theory, running it hard off the showroom floor does a better job at breaking in the engine. You can check out the theory and description here.
As expected some of "The Guys That Ride" at MotoSport broke in the engine of their new dirt bike(s) using a variation on the heat cycle method. The following is one way a MotoSport employee used to break-in his dirt bike:
Let the bike warm up normally, then ride the bike for around 10-15 minutes at a decent pace but without over-revving the engine. Then let the bike cool down for around 20-30 minutes. Then repeat this 3 or 4 times. On the 3rd and 4th time I usually ride a bit longer, 15-20 minutes.
2-stroke or 4-stroke - proper engine break-in is key for a long lasting engine
Whatever method you employ, the good news is you can use the same process to break in a new engine or rebuilt engine and it doesn't matter if the bike is an 80cc or a 450cc engine. However, it is crucial that you properly warm up the bike prior to riding a new or rebuilt engine.
All the new parts in the engine are mating together and the aluminum parts need a chance to expand, from the heat, fully. Riding before the engine is warm (and this reflects both the heat cycle routine and the controversial ride it hard off the floor) can cause the pistons and rings to sit prematurely causing wear and potential damage.
Therefore, a good rule of thumb to determine if your bike is ready to ride - place your gloved hand on top of the radiator cap. If you can feel heat, you're good to go.
After the first day of engine break-in, change your oil. Whatever break-in method is used, know that metal shavings will be in the oil and need to be flushed out. Drain the day's oil and change the filter. It's actually a good idea to fill the engine with a fresh quart of oil and drain again.
Let us know what engine break-in methods work for you and better yet, what hasn't worked.