The ATV engine break-in procedure for a new motor is highly debated topic among professionals and amateurs alike, and rightfully so. It's an important part of a new ATV engine's care, and it will have a considerable impact on how your new engine will perform throughout it's life, and indeed, how long that life may be.
Flat Spots on the Same Motors Using the Same Technique
Of the dozen or so new engines we have owned, two in particular stand out when we discuss engine break-in - a pair of 600cc, in-line 4 cylinder Yamaha engines.
We had two of the same brand new engines and broke them in literally side by side, using the same manufacturer recommended "slow and easy" technique.
Both engines suffered from very noticeable "flat-spots" and "rattles" when at certain different RPMs. It wasn't until years later that we realized why those flat-spots might have happened at the same place on both motors, and we are certain it wasn't something inherent to the motor design.
It was likely because they were the same RPM levels that Yamaha suggested as "limits" when breaking in the new motors. There was a 6,000 RPM limit for part of the break-in period, and a 7,500 RPM limit for the another part. Red-line on these particular engines was around 10 or 11 thousand.
At 6,000 RPM there was a definite flat-spot that you would notice when accelerating on a smooth surface, and at 7,500 RPM there was a loud rattling noise if you ran the engine steady at that RPM.
The Engine Break-In Method That Convinced Us
Breaking in an ATV engine can be risky for the engine if not done correctly. There are also occasional defective engines that will be bad no matter how you break them in.
With that in mind, here is the method we have used with good success on performance motors:
Warm it Up, Rev it Up
Warm the engine completely, usually about 4 - 6 minutes, depending on many things including the engine size and if it is liquid cooled. Larger engines take longer to warm up, as do liquid cooled engines.
Once completely warmed up, go out and ride the ATV and put a load on the engine by opening and closing the throttle hard in as many gears as possible, alternating between short bursts of hard acceleration and deceleration.
Ride for 3 to 5 minutes using the entire RPM range then shut off the ATV and let it cool completely. While it's cooling off, check the ATV for loose nuts, bolts, leaks or other things that may have come loose during the initial ride.
Once the quad has cooled completely, repeat the process several times, each time riding a little longer than the time before.
Change the Oil and Filter
After an hour or so of riding the ATV then cooling it off, be sure to change the oil. On a new engine, the first hour of operation will remove all burrs from the motor parts and they will be mixed with the oil and trapped in the filter.
Continue riding with varied acceleration for several hours, and change the oil at least once more. You almost can't change the oil too much.
Something to keep in mind about riding your ATV is you should always warm it up before you ride, especially if you're going to ride it hard. If you are just putting around camp or going down to the mail-box it's safe to start it up and take off within 5 seconds or so, just long enough to make sure the oil is circulating through the engine and you don't romp on the gas right away.