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Discussion and questions related to the course Practical Engine Building
what is break-in oil ?
what is the function of break-in oil ?
how to use break-in oil ?
Engine break-in oil is very importan in new engines and rebuild.
This ensures that all surfaces within the engine are fully mated, particularly the piston rings and valvetrain
It is crucial to choose the correct engine lubricant; are usually used conventional oils for two reasons: They provide both full hydrodynamic films and also allow for sufficient friction and heat to properly wear mating parts together.
If you'll open manuals from Manley, Total Seal, JE Pistons, Mahle and others you'll find that they don't recommend using synthetic oils during break-in process as they reduce friction too much. Break-in oil is basically an oil with reduced friction properties yet still good thickness...
Many of them will also include specific additives, such as additional detergents, zinc, and others, to improve the break-in process while reducing wear where it isn't wanted, such as pushrod engines' flat tappet camshafts and followers.
Oil is "relatively" cheap - my preference is to use the running in oil, run the engine up to temperature, at 2k rpm for pushrods or OHC that rely on splash lubrication, while checking for leaks, or other issues. Then drain the oil, replace the filter (always worth cutting it open to check for suspect for warning signs) and refill with the new filter and more running in oil. After break in, tuning, etc. however long that is, drain and change filter (check again) and refill with the oil I'll be continuing with.
If you can't get the break-in oil where you live, a straight grade mineral oil like, SAE 30 or 40, will work almost as well, with the changes mentioned above.