You ask we answer. Here's the latest in our "Ask A Mechanic" series.
Q: What's the best way to break in a new piston?
A: Replacing the piston on a dirt bike (or ATV) hardly embodies an entire engine rebuild however the same principles apply when breaking it in. When you perform a "top end" you replace the piston, rings, pin, clips, gaskets and on 2-strokes the needle bearing. As you see, installing a new piston involves replacing other small parts that all need breaking in. A proper break-in period helps seals the piston rings into the cylinder surface, otherwise expect engine issue down the line.
Ask one rider how to break in a new piston and the answer probably differs from another. You get some who believe in a variation of the "ease into it" routine while others advocate ride it like you stole it. However, the one common denominator in all break-in theories includes the heat cycle. You have to conduct a heat cycle. Most riders perform a "three heat cycle" meaning a warm-up then letting the engine cool off completely before another cycle and doing so three times. Here's what one MotoSport employee said about their break-in routine:
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.
Read How To Break In a Dirt Bike Engine to learn more about the new engine or piston break-in process.