By Francisco Aristizabal
There are many factors involved in a successful engine overhaul process. An experienced technician, a machine shop with the appropriate knowledge, and appropriate equipment are all important. In addition, you need the best quality spare replacement parts. However, these efforts mean nothing if the break-in procedure is insufficient.
All the new parts assembled or resurfaced need an adequate initial run-in period to mate to one another. This is true of the complete engine system assembly – bearings, valve train parts, but mainly piston rings must expand and seal into the liners and/or cylinders. Their contact surface/coating must be matched with the liner/cylinder surface, establishing a good mating surface for maximum performance and long engine life. This is especially true for diesel engine applications: the first 120 miles or 200 km for a truck, or 100 operation hours. For construction/industrial or agricultural equipment, break-in is still essential, although you may utilize alternative break-in procedures. Depending on the type of equipment, some may require particularly heavy engine loads with minimal idling to help seat engine components properly.
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In a truck, a full vehicle’s load operation with a throttle maximum range of 75-80% for the first 120 miles or 200 km assures good combustion forces into the cylinder, spreading out the rings against the liner’s walls, generating an adequate oil film control and sealing. In the same way, an agricultural piece of equipment must be operated with the plowing implements down in the land, forcing the engine under “controlled operating conditions” of load during these first stages. Make sure to avoid overspeed and long periods of idling.
A misunderstood concept, particularly in some Latin America markets, operators may confuse break-in with very long idling periods after an engine overhaul. This usually ends with awful consequences like high oil consumption, breakdown of the oil film and incomplete combustion due to the lower temperatures in the piston crown and no thermal load on the system are commons practices unfortunately. A proper break-in process keeps combustion gas blow-by and oil consumption to a minimum.
Recommendations for the break-in process after a rebuild
- Start the engine and idle for no more than 5-10 minutes, this is a good time to check for leaks, oil pressure, coolant temperature, and any other operational condition.
- Follow the alternative break-in procedure, depending on the application (truck, marine, industrial, etc.) according to OE; always avoid a no load or overspeed operation.
- Always use a break-in oil for the initial period (100-500 hours) if possible. These oils are formulated to provide a controlled environment for piston rings and cylinder liners; at the same time, break-in oils could provide the necessary wear protection for the valve train and gears.
What we mentioned above is intended to serve as a general guide. Specific diesel engine break-in procedures may vary depending on the manufacturer/application. Always check with the OEM service literature. In addition, the AERA tech line is available to help solve any questions you may have.
Read this article with all images in the digital issue of Engine Professional magazine https://engineprofessional.com/2024EPQ1/#p=96