Breaking in a new motor

[Arthur Grant]

Team,
I am looking for some serious answers because financially I can't get this wrong. Just had my engine rebuilt, nothing special, just re-manufactured. I am in break in now, have about 50 miles on it. Chasing a couple of electrical gremlin. When I get it back was looking to put around 500 miles on it, change out the oil and filter again. The question since I may compete this car again if I am not forced to sell it, is there anything beyond the usual gentle break in miles I need do to assure I don't bring the car out and end up destroying it?

Thanks, just looking to leverage your experience.

[Bobby Beyer]

Keep an eye on the oil pressure, oil level, and make sure the tune is good. Other than that follow the OEM break in procedure, aka avoid highway driving or long stints of constant RPM, and don't beat on it. Stop and go traffic is a really good way to break in a motor.

[Mako Koiwai]

Some folks say that synthetic oils are too slippery for "proper" break-in.

[KJ Christopher]

Some folks say that synthetic oils are too slippery for "proper" break-in.

That would depend on how it was built. Could go either way.

[Bill Martin]

Several modern performance cars like Vette and Evo come with Mobil 1 installed. Those factories must not believe in non-synthetic break in.

Actually break-ins are mostly old school. With more modern tooling, engines are better built than they used to be. Break in is mostly about wearing down the various unintended high points on machined surfaces. They don't worry about that as much any more. Mostly owners manuals warn against extreme usage such as high speeds, trailer towing and such.

I think the biggest remaining risk is damage to cam lobes and lifters due to the removal of zinc and phosphorous anti-scuffs from modern oil. If I had to choose between 500 easy miles and a can of break-in additive from a camshaft company, I'd go with the latter.

[Bobby Beyer]

Well from what was always explained to me, there is really only 2 items that need to be worn in during break in. Cam lobes on flat tappet engines, and piston rings, most modern engines don't use flat tappet cams so that shouldn't be a worry. As for breaking rings in, the main goal is to keep the bore from glazing over, which is mostly a side effect of coked up rings, which you're more likely to encounter during the first few hundred miles of driving than anywhere else. That's the reason you shouldn't be driving on the highway because the load isn't great, which doesn't allow the combustion pressure to force the ring against the bore allowing combustion byproduct to gather on the ring. That's the reason it should be driven during stop and go traffic because the varying loads create uneven force against the rings allowing a more even wear process on the bore and rings.
With my motor I chose not to use synthetic because I'm cheap and it was an easy way to save 40-50 dollars in the first few hundred miles of driving. Given my bearing clearances and the fact the motor was never originally spec'ed with synthetic I didn't feel it was going to be an issue.

[Mako Koiwai]

Subaru, at least use to, recommend dino oil for break-in, in order for the rings to seat themselves properly. I didn't know that and at 75 miles put in Mobil 1. I never had as much compression as I should have, but with a turbo motor I wasn't too worried. In fact I thought the fact that I never had any of the typical suby engine problems might have been because of that (along with colder plugs for my tune)? Suby cylinders have a teflon coating that gradually wears away during break-in to especially help against piston slap with the boxer engine.

[Bobby Beyer]

Usually its the pistons that have the teflon coating not the cylinders. I know my Mustang had teflon lined skirts from the factory, and my OE replacement Mahle pistons had teflon lined skirts and a really trick anti stick/slippery graphite coating. On the motor I pulled apart with 265k and worn out bores, the coating was still visible, so that stuff really does last a long time.

[Pete Loney]

From the Flyin Miata Website....

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 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 heavy 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 “heavy 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.

Once you have done the ring seating, try to control yourself (or at least your right foot) for a few hundred miles, no full throttle, try to vary rpm on the highway and no revving to the limiter.

[Ed Holley]

What Pete has posted from Flyin Miata, in concert with what Bobby is recommending, is how I have always approached engine building and break-in of "old school" normally aspirated engines, whether it be a Cortina FF motor, or a Ford or Chevy V-8. If I were rebuilding my 1.8 Miata motor, it would be approached the same way.

[Arthur Grant]

Thanks all