Flyin' Miata : Tech : How to break in an engine

Everyone has their own idea of how to break in an engine based on what their father told them, manufacturer suggestions, half-remembered lore and best guesses. Our break in procedure was developed from talking to other engine builders, piston and ring manufacturers. It works quite well in our experience.

All of our engines are shipped dry. Double check the oil drain plug, install a new quality oil filter and fill the engine with approximately four quarts of straight 30 wt detergent oil. We recommend a change of oil and filter after 25-50 miles, again using straight 30 wt. If you plan to switch to synthetic oil, please wait for at least 1,000 miles.
Use all new coolant lines and clamps to avoid leaks.
Mix anti-freeze and water at the minimum concentration to get the freeze protection that you require. Water transfers heat much better than anti-freeze. Not a bad idea to check or replace the radiator cap while you’re at it, as most of the ones we test fail a pressure test miserably. Jacking the nose of the car up while filling with coolant ensures that the fill point is the high point of the system.
Make sure you have all your ground wires hooked up! Missing grounds can make smoke come out of expensive places.
Have your timing light already hooked up before starting the engine and have an assistant watch for leaks while you start the engine for the first time. We pack the oil pump with engine lube, so oil pressure should come up very quickly. Start the car, watch for oil pressure while your assistant looks for leaks of any kind. Fuel leaks can be especially unpleasant.
Once you have verified oil pressure and no leaks (or fixed any leaks), set your ignition timing while the car is warming up.
DO NOT let the car sit and idle for a long time. Once you’ve got timing set, no leaks and everything sounds and looks good, take the car out on the road.
Keep in mind that there really shouldn’t be any metal to metal contact happening within your engine, other than the rings to the cylinder walls. The rings are the ONLY things we are interested in breaking in or seating. What seats rings is cylinder pressure. Rings and pistons are designed so that cylinder pressure sneaks behind the compression rings and forces them out against the newly honed cylinder wall. Why do I mention this? Because I want you to take your warmed up car out on the road, find a nice straight stretch and do a couple of full-throttle runs in third or fourth gear from about 2500-5500 rpm. Each time you hit 5500-6000 rpm, snap your foot off the gas and let the car coast down to 2500 rpm while in gear, to pull high vacuum in the cylinders. Repeat this step about five times and you should have a nicely mated set of rings and cylinders. NOTE: When I say “full throttle”, I am referring to a normally aspirated engine. For a turbo or supercharged car, modulate the throttle to achieve about zero on your boost gauge, rather than full throttle. This would be roughly equivalent to full throttle in a normally aspirated car.
Take it home, recheck for leaks, make sure fans work, etc and then change the oil.
That’s it! Have fun!