Engine Break-in Procedure
Posted by Scott S. on 19 October 2010 12:37 PM
Getting a new pocket bike or scooter is exciting. The first thing you want to do is gas it up and race it against your buddies, or just see how fast it can go. However, if you want to get the most speed, responsiveness, and a long life out of your engine, it is important that you follow these break-in prodcedures:
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:
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: