Breaking in an Engine

2010

The process of breaking an engine in truly deals with every component in the engine. What occurs is the high spots or rough edges of the components are being removed by metal-to-metal contact with the mating surface. This process is occurring on a microscopic level.

A second reason to break-in the engine is to normalize the stresses internal to the components. During the casting and/or the machining process the material can cause internal stresses. The best way to relieve these stresses is through the means of heat. Since the engine will generate its own heat during running this will accomplish the goal.

According to Briggs and Stratton’s testing using stock engines, the best break-in procedure is as follows:

1. Start engine and apply a load that will require 1/4 throttle maintaining 3600 rpm for 15 minutes.
2. Apply a load that will require 1/2 throttle maintaining 3600 rpm for 15 minutes.
3. Repeat procedure 1 then 2 for one hour.
4. Apply a load that will require 3/4 throttle maintaining 3600 rpm for 15 minutes.
5. Repeat procedure 2 then 4 for one hour.
6. Apply a load that will require full throttle maintaining 3600 rpm for 15 minutes.
7. Repeat procedure 2 then 4 then 6 until finished. (Usually 10-15 hours)

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