FWIW, here's something I've posted several places in the past in response to similar questions:

The entire point of break-in is to let the parts themselves do the final "machining" and wear themselves into the best possible fit/mating. As machining technology gets better and better, break-in becomes less important... but final "wear-in" is still important. You want to wear down the high-points (on a microscopic scale) without doing it so fast or long that your generate localized heat which causes a "microweld/micro galling," leaving a micro pit or bump. As such, short bursts toward redline (not under load) actually will help "wear-in" the parts. Short burst of acceleration also help, e.g., accelerate for a couple of seconds and then back off. What hurts during break-in are either sustained running at high speed/load, or running at a constant load/speed for a sustained period of time. With different speeds and loads, different areas (again on a microscopic level), tend to be the "high spots."
Think of it as trying to hone the parts together as you would sharpen a knife, with the varying speeds and loads as moving the knife to different angles, but not wanting to get the knife blade hot.

Understanding what you are trying to do is more important than slavishly following the rules ("Gee, I just hit 1,000 miles so I can nail it!). Think of the first 1,000 miles as being similar to a ten minute "limbering up" prior to exercise... start easy the first few miles and gradually work up to normal running over the first 1,000.

WIll disaster come if you don't do this? Probably not. But doing it will increase the odds that you have a trouble free engine that goes 200,000 miles, vs. one that has a bearing problem at 75,000 - 100,000.


Note: When I talk of hitting redline, I'm talking of a very short burst of the engine while it is not under heavy load, e.g., a throttle "blip" in neutral or during a lightly loaded upshift. The "couple of seconds acceleration" I mention is under load while driving and should not ever be near the redline of the engine while breaking it in.

Some people propose to "break it in hard," suggesting that this gives more power. Well, there is some truth to that... but not in the way many people think. Most engines (if maintained) will actually hit their peak horsepower during their life somewhere around 30,000 to 50,000 miles. This is the point when parts and clearnaces have worn to the point that friction is reduced; however, not to the point where compression or other power-robbing things happen. So, if you break it in hard, yes, you might see a tad more power. But that's because you have shortened the life of the engine considerably with excess wear aging it prematurely.

P.S. for those who say engines nowadays are already "broken-in" as they come from the factory due to more precise machining, I did an oil analysis on my Z4 from new. In the first 2,000 miles there was approximately five times the wear metals as in the second 2,000 miles.

Yeah, I don't think i know of any gas powered engine that does not produce more filings in the initial operation than later.

Anyway, I don't mean to be a smarta$$ but if you lease your car for 3 yr/4000k then it can be good to break-in hard? i mean you won't necessarily have to vehicle for a long time right?:dunno: :popcorn:

The only parts that are really breaking in during break-in are the piston rings and the cylinder walls. The journals don't really contact the bearings as they ride on a hydrodynamic film. The only time you'll have piston v. wall issues (and even this wouldn't be micro-welding) is if you have an extreme lean condition or you have detonation. This is only a concern with motors that are built beyond OEM spec's and need to be tuned before they can be operated.

You don't have to worry about 'micro-welding'. All metal-metal parts are already heat-treated at the factory. You're not going to reach temperatures high enough to damage that unless you start having conditions that would cause spun bearings- lack of oil-pressure situations. Even then, the journals are usually not damaged because of the heat-treating.

As for breaking-in your engine without load: you may not as well do it then. The point of load is to increase heat in the cylinder so that the piston expands putting pressure on the rings against wall. This is what fully seats the rings. Mahle engineers and highly regarded engine builders agree with this.

Btw, that 4,500rpm limit has to do with the transmission and not the engine. There's nothing in the engine that would be affected by max engine speed during break-in. The 4,500 limit is to limit the speed of the transmission components to break-in the clutches. This why the best way to break the engine is to use manual mode do your high-load burst in 2nd or 3rd gear, go to redline, and engine-brake before you get to redline (the engine braking part is important also).

I'm not quite sure why you wish to be so disagreeable as to disagree with things I never said, but when you say "As for breaking-in your engine without load," I must point out that I never said any such thing in my post. Just because part of my suggested "break-in" proceedure says to avoid redline under heavy load, it most certainly does not suggest that the entire break-in period is "without load." I certainly cannot see anywhere in my post where the words "without load" are used.

And, quite obviously, when I say "Think of the first 1,000 miles as being similar to a ten minute "limbering up" prior to exercise... start easy the first few miles and gradually work up to normal running over the first 1,000," the clear implication is that you are increasing the loading during the break-in period such that at the end of the period you are applying full-load for longer periods of time.

And, as I pointed out, I have some limited data... "In the first 2,000 miles there was approximately five times the wear metals as in the second 2,000 miles."

Whata data do you have to share?

P.S. If micro-welding is not a concern due to heat treatment, I wonder why Dana corporation bothered to apply for this patent?

http://www.patentstorm.us/patents/7121192/fulltext.html

Note from the Dana Corp patent "There is a critical time period for new engines known as the break-in period during which the moving surfaces of joined components adjust to matingly conform to one another. During this break-in period the piston/piston ring interface is particularly susceptible to a condition known as microwelding, wherein there is a propensity for the piston aluminum to transfer to the sides (typically the lower flank of the piston ring. "

But then what do Dana Corp engineers know about engines?

Actually, I worked for a diesel engine-maker and some of the people I worked under were ex-Mahle engineers. Mahle is a German company that's a piston supplier to basically every oem in the world (including BMW). So yes, I'll trust them over an American automotive parts company. Btw, you realize Dana doesn't even make powertrain products right?

You said to redline to the engine in neutral lol. There's almost no load at all in that situation. Redlining without load is just wasting gas. Once again, you want the piston to put pressure on the rings. The ideal would be to make short medium-highload bursts from 0 miles.

These days most engine-makers primarily cold test (testing the engine without combustion) at the factory because it's more efficient, but still a small percent are hot-tested. Just 5-10 years ago, 100% of engines were hot tested. Hot-tested engines are bascially broken-in in the factory. Guess the procedure for hot-testing an engine. It's not what you're suggesting ;).

I am afraid I don't agree with your contention that the way to break an engine in is to have full-load bursts to redline starting from zero miles on the odo. We'll just have to agree to disagree on that one and let others make up their own minds.

As to the concept of break-in risk of micro-welding, basically you are saying that the Dana patent application is lying when they talk of micro-welding between the rings and the pistons during break-in? ("You don't have to worry about 'micro-welding'. All metal-metal parts are already heat-treated at the factory.")

It's too bad the patent examiner didn't have your expert opinion available when they reviewed the patent -- they could have rejected it rather than issue it.

P.S. Here's a link which has a mention of what GM, Ford, and Honda engine experts think about high-loading break-in from zero miles:

http://www.motortrend.com/features/e...nce/index.html

Actually, in this link no where do they say that high-speed, high-load break-in is bad for your engine. All they say is that it's payoff would be smaller due to finer cylinder honing. That discounts your arguement even more. There's no reason not to have fun with your new car then.

Btw, I worked in engine development and subsequently also in one of the plants. Believe me that the hot-tested engines undergo everything that you're saying shouldn't be done with a new engine, and the ones I worked with see a LOT higher load than these consumer engines.

Why I'm discounting the Dana link is that they have no powertrain products whatsoever. It's not their expertise by a mile.

From the article: "But if his procedure works, why don't manufacturers perform it in the plant on a dyno, especially on performance engines like the handbuilt Corvette LS7 and supercharged Northstar? They would, but Lancaster and Herr confirm the only engines that get such treatment are those undergoing torture-testing during development to ensure that the Motomans of the world won't ring up big warranty claims."

As for Dana "no powertrain products whatsoever," I didn't realize that differentials and such were not part of a powertrain. But you do have a strange criteria, at least in my opinion. Using your logic one could just as easily have rejected Honda engineer's work at various points over the years since, at any given point in their evolution, they had no experience in motorcycles, automobiles, powertrains, and, right now, none in airplanes. So, using your logic, surely any patents they are currently getting for the plane they are developing are to be ignored since Honda "have no airplane products whatsoever. It's not their expertise by a mile." As could be said as well of Apple back before the i-pod was launched, e.g., Apple have no audio products whatsoever. It's not their expertise by a mile.

They are performed on plant dyno's. That's how 100% of engines used to be tested on the engine plant-dyno's not too long ago. In the interest of efficiency, most engines are now cold-tested, but about 2-3% are still hot-tested. The hot-tested engines go to customer vehicles just like the cold-tested ones. About 20sec worth of testing v. a few minutes. Cold test engines are integrated into the line. Hot-test cells require a person to set the engine up prior to the test, and post-test as well. What they're saying is that it's not required as much, not that it's bad for the engine. Would you like to guess how Formula 1 and LeMans engines are broken-in on engine-dyno's? :)

Powertrain is engine and related components. Drivetrain is everything after the engine: transmission, driveshaft, differential, transfer case, axle, etc.

The Honda engineer concurred that the benefit would smaller than in the past. Point out where they indicate that such a break-in procedure is bad for the engine. It is amusing to watch your argue based of a snippet in a magazine.

There will never be agreement on this topic, my experience in BMW parts and service of over 20 years has not produced a single case of problems related to breakin. The argument that the engine will be better on fuel mileage if broken in also has no provable studied that I can find.

Drive the car like you do every day and forget about it.