47cc or 49cc New Engine Break-In Procedure

As mentioned in our starting troubleshooter, in order for the engine to operate correctly, it needs good compression. Another way to word this is that the piston and the cylinder it travels in must have a very good seal as the piston reciprocates. Every time ignition occurs in the cylinder, the exhaust gasses should only go out the exhaust, and new gas/air mixture needs to be sucked in from the carburetor. No gasses should make their way over the sides of the piston, as this would 

Two stroke engines used in pocket bikes and mini bikes can reach rotational speeds of up to 9,000 rpm. This means that the piston can move (stroke) up, down, up, down — up to an astonishing 300 times per second. At such speeds, the cylinder gets incredibly hot. This is especially true on air-cooled models.

The only thing protecting the piston rings as they rub against the cylinder is a thin film of oil that builds up on the cylinder walls. The purpose of breaking in the engine is to set the piston rings to the cylinder walls. This means physically mating the engine's rings to its corresponding cylinder wall - wearing in the new rings so that they match the cylinder on a microscopic level.

Properly set & worn-in piston rings will not allow gasses to escape past the rings into the crankcase of the engine. This is referred to as "blow-by", and if you ever take apart an engine, you can see it as brown smudges on the sides of the piston. Blow-by will speed up premature engine wear and sooner or later, the engine will fail. The key to proper break-in is to let the piston rings wear in, but not glaze over. Glazing over happens if the temperatures in the engine get too hot. The oil in the premix disintegrates and no longer lubricates the piston and cylinder.

These are sample pictures of a pocket bike engine we recently disassembled. This person did not use the correct oil mixture:

This is what will happen to your engine if you mistreat it! In the left and right pictures, you can see visible yellowing on the piston. This happened because the piston was not getting properly lubricated and the friction / heat of exploding gasoline caused it to overheat, causing it to chemically react. The middle picture shows excessive carbon buildup. This happened is this customer called us complaining of poor engine performance. When he found out he was using half the oil required during break in, he re-did his mixture and put in more oil (which contributed to the soot buildup), but it was too late because his engine already lost its full compression due to the damage. We also believe that the oil he used is of a low quality, as high quality oil will not cause so much deposits. You can imagine his spark plug did fare well either. He needed a complete engine head rebuild. So take care of your engine, and don't let this happen to you!

Recommended engine break-in procedure:

1. Mix up one gallon of fuel. Use a 25:1 fuel/oil mixture during break-in. This is equivalent to mixing 5 fl. oz of 2-cycle oil to 1 gallon of gasoline.
2. Start up the engine and let it idle for a few minutes (3-4 minutes is perfect) to bring it up to its operating temperature.
3. Kill the engine and let it cool down (8-10 minutes will suffice). This step is very beneficial to begin the process of setting the rings properly without "glazing" them due to overheating.
4. Start up the engine again and take your pocket bike for its first ride. Limit the ride to 10-15 minutes. During your first ride:
   • Limit full-throttle acceleration to a spurts of 3 seconds.
   • Do not race the bike at full-open throttle for longer than 3 seconds.
   • Do not ride up any hills, and do not exceed the maximum load capacity.
   • Try to alternate the engine RPM's as much as possible. The best thing to do is cruise at varying speeds, occasionally letting off the throttle, accelerating, then decelerating.
5. Kill the engine and be sure to let it cool down completely again after this ride (20 minutes).
6. On subsequent rides, gradually increase the engine load. Limit your wide-open-throttle usage to 5 seconds, and limit ride time to 15-20 minutes (less if outside temperatures exceed 100 °F).
7. Your engine is fully broken in once you use up the entire gallon you mixed up in step 1. Switch to 4 fl. oz of quality, premium 2-cycle oil to 1 gallon of gas (32:1).

It's a good idea to check the spark plug after you use up your first gallon of fuel. The condition of the plug will tell you a lot about the quality (and ratio) of the oil you are using:

• Grey: not enough oil used/engine overheating
• Bronze: perfect
• Black: Too much or low quality oil used