Far be it for me to always agree with Dar, however I have been using the break-in method that he talks about for years and my engines are very, very strong. Even my “propped” ducted fan engines still have pinch at the top and the con-rods are tight after countless gallons of high rpm abuse and three or four normal interval bearing changes. Same thing can be said of my OS and YS two stroke sport engines.

Running-in a tapered-bore engine slow, cold, and excessively rich in many cases leads to reduce power potential and service life. Some guys run them in cold and of course a great majority of the engines run afterwards, yet they have no basis of comparison so they are content with the engine’s anemic performance.

Many times guys have said to me, “Is that only a XX size engine?”, “is that engine stock?” or “why is your engine so much stronger than mine, I’m running the same setup as yours”. I have a look at their engine and it has less compression (pinch), excessive rod play and their engine is much newer. The guys swear they were never run lean. The differences? How they were broken-in.

Why do some manufactures recommend the cold, drowned in fuel, four stroking method break-in?
They probably figure it’s safer than an engine ran too lean, for that will have a much greater chance of damage than one that’s too rich. In other words it’s better to error to the side of less engines totally “lunched” and more engine still running, but just OK.