Paul H. (in MD)

I have to admit, I have to laugh when people post 2-3 paragraphs and then put (long) in the subject. This post should set new standards for the use of the term "long"..

What follows is a VERY long explanation of engine break-in procedures as applied to a Saturn twin-cam engine. Perhaps I should break it up into sections? It was posted to the Saturn mailing list a LONG while ago (early '96?). It is generally considered to be excellent.

Note: Please read the entire article before you comment on such things as the suggestion to use full throttle at less than 100 miles (first remember it is only 2-3 seconds at low RPM, and the technical reason for making this suggestion is given later in the article). Also, to apply this to an Audi engine you may wish to substitute 1000 miles for the first 500 miles, and 5000 miles for the first 3000 miles in the "Practice" section.

I am posting this here without the permission of the original author, mainly because I have no way to get in touch with him to ask! If everyone approves, then perhaps this can be added to the FAQ (Frequently Given Answer) section?

Enjoy!
Paul
--
Ben Slosser's guide to 4-stroke engine break-in:

The Practice.
>For the first 100 miles, only take short trips of <15 minutes. Do not rev above about 3500 rpm. Use full throttle in short (2-3 second) bursts at low rpms (say 2500) - 5th gear on the freeway is ideal for this. Do not do more than one full-throttle burst in the same 2-minute period. Avoid driving for more than 2-3 minutes at the same rpm - if you are on the freeway, vary your speed and alternate between 5th and 4th gears.

>From 100-500 miles, increase the peak RPM you reach by 200 rpm each time you drive the car (but don't go higher than redline). Do not rev to your new peak under heavy throttle; instead, let the engine drift up to the rpm under light load. For instance, pulling away from a stoplight, leave the engine in first and accelerate lightly until you reach the desired RPM, then shift. Continue the full-throttle-burst procedure. Do not rev the engine high under full throttle, and do not do either the peak-revving or the full-throttle procedure more often than once a minute. Avoid driving for more than 5 minutes at any one rpm - again, alternating between two adjacent gears and varying your speed will work.

You will notice that each time you reach a new peak rpm, the engine will be quite loud at that rpm, but after a few runs up it will quiet down. This is a sign that the break-in is proceeding well. You will want to have revved the engine to redline a few times by the time you reach 500 miles. At that point I recommend you change the oil, as most of the metal wear and contaminants from break-in are released in the first 500 miles. [Editor's note: I would not recommend doing this with an Audi engine. At least as far as the 1.8T, it is HIGHLY recommended you WAIT until at least 5000 miles before the first oil change. -pwh]

>From 500-3000 miles (the extended break-in) you can operate your engine fairly normally. Most of the work is done. You should still run the engine at higher RPMs on a regular basis (assuming you don't in the normal course of driving ;-) ) and you should avoid prolonged high-speed/high-stress operation, like racing or cruising at 110 mph. I personally change the oil after 1500 miles [Editor's note: Again, wait until at least 5000 with an Audi engine. -pwh] since it will be dirtier at that point that it would be after 3000 miles of post-break-in operation, but it isn't critical. Be sure to change it at 3000 miles, however. Although there is some difference of opinion on what KIND of oil to use during break-in, the general consensus is to use normal (non-synthetic) oil of the recommended weight (5- or 10-30).

>From 3000 miles onward, your engine is considered broken in. It will probably continue to "loosen up" a bit over the next 3000-6000 miles, so look for a small increase in gas mileage. Other than that, your engine is now be ready for a long and productive life. Enjoy!

***** BEGIN TECHNICAL SECTION *****

[Some of this is what I remember from articles I have read and discussions. I cannot vouch for the complete accuracy of what follows, but I believe it to be essentially correct. If you *must* flame me, please do so in private unless you think I've made a mistake which everyone need to know about to avoid doing something unpleasant to their car]

The Theory.
The primary goals of engine break-in are: 1) achieving a good seal between the piston rings and cylinder walls, and 2) allowing the engine to operate correctly throughout its RPM range. The major enemy during the break-in period is localized heat buildup, mainly in bearing surfaces (most notably the crankshaft bearings).

Initial state:
When the engine is machined at the factory, many wearing surfaces (places where parts rub against each other - cylinder walls, bearings, etc) are purposely machined more roughly than they could be. The reason for this is that it allows the engine to complete the machining/polishing as it operates, thus allowing for the individual variations inherent in any manufacturing process. This wearing process, when complete, produces parts which will fit together with very tight tolerances. However, the process also involves a great deal of friction, which in turn means a great deal of heat. As metal parts heat, they expand slightly. If the expansion goes beyond a certain point, the parts will tend to bind with and/or score each other. This must be avoided.

[To put this in plain english, the parts which rub against each other are left a bit rough, and as the engine runs the parts will scrape against each other until they wear down a bit and have a proper fit. While they're still in the process of scraping, they can get very hot; if they get too hot, they will damage each other in a permanent way.]

Since this sort of heat buildup is very localized, it will not show up on the engine temperature gauge. Therefore, it is important to operate the engine in such a way that the heat buildup will not reach a dangerous level. More on this later.

Stress and Variation:
Although the engine parts are metal and, as a rule, quite rigid, they are still subject to slight deformation when stress is applied. The largest stress in a piston engine is that produced by reciprocating parts. The forces involved increase as the square of the RPM. Any deformation will necessarily involve a change in some tolerances inside the engine. Thus, in order for the engine to operate properly over a range of RPMs, it is important that it be exercised over this range during the break-in process so that the wearing parts will experience the range of tolerances they will be subjected to during normal (post-break-in) operation. Further, for the wearing surfaces of reciprocating parts (most notably the piston ring/ cylinder wall interface) operation at a single RPM for an extended period of time will cause the machining process to progress significantly further within the confines of the part's range of travel without progressing at the point just outside that range, thus building up a small ridge of metal just above the point of maximum excursion.

[In order for your engine to run well from 1000 to redline, you need to operate it at all those rpms while it is breaking in. If you don't, the parts won't be used to working at the rpms you neglected, and they won't work as well at those speeds]

Piston Ring Sealing:
The seal between the piston ring and the cylinder wall is crucial to getting good economy and performance from the engine. A bad seal will allow more blow-by, reducing the amount of power the engine can produce with each power stroke and thus reducing both its horsepower and fuel economy, as well as allowing combustion gasses to get into the crankcase and contaminate the oil AND allowing oil to get into the combustion chamber and be burned, producing the characteristic blue-smoke-from-the-tailpipe syndrome (note that oil can also get into the combustion chamber via the valve stem guides, but that's not something we can do much about during break-in).

The key to getting a good piston ring seal is high combustion chamber pressures. Embarrasingly, I don't know why (can someone fill me in?). High combustion chamber pressure is produced under hard acceleration; also, the lower the RPM the longer that pressure is maintained during each power stroke. SO - to get a good piston ring seal, hard acceleration at low RPMs will give the best results. Since hard acceleration also produces more heat and more stress (leading to friction and still MORE heat), it should only be used in brief bursts, followed by a couple of minutes of "normal" low-stress operation to allow the heated parts to cool down.

Localized Heat Buildup:
As previously mentioned, wearing parts will produce inordinate amounts of heat as they polish each other. This produces local points of intense heat inside the engine, with temperatures far higher than the engine as a whole (which shows up on the temperature gauge) or even of the surrounding parts. The most susceptable points in an engine for this kind of heat buildup are the crankshaft bearings, which must withstand enormous stress and pressure. If the bearings are allowed to get too hot, they will expand to the point of scoring each other or (*gulp*) binding, producing a spun bearing. During the initial stages of engine break-in, there is no satisfactory way of keeping these bearings cool during even mild engine operation except to turn the engine off after every 10-15 minutes of operation and allow the bearings to cool down.

The theory I have outlined about should now be sufficient to explain the "practice" section of the break-in instructions. For the first 100 miles, keep the rpms low and the trips short to minimize the stresses and heat buildup in the bearings, and use short full-throttle bursts to seal the piston rings. From 100-500 miles, gradually increase the RPMs to allow the wearing surfaces to correctly mate, and continue using full-throttle bursts to ensure ring sealing. Use cooling periods (the 1-minute rule) to minimize the heat buildup produced by the high RPM operation and the full throttle bursts. At 500 miles, change the oil to flush out all the metal particles produced by the wearing process. [Except in an Audi. -pwh]

I hope everyone finds this information useful. If you have comments which are of general interest, please post them - if you just want to flame me for making a mistake, please email me so that we don't make everyone endure a huge firestorm. I should also note that I practice what I preach - at 5000 miles my CBR is more powerful than anyone else's I have ridden and its oil is clean after 2000 miles of operation, while my Saturn SL2 (though at only 1000 miles) is getting 29 mpg overall and revs quite happily to redline.

Best regards,
Ben

mpm

No offense, but I stopped reading when I saw Saturn. I think you made a wrong click some where

Oggie

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Paul H. (in MD)

No wrong clicks. I post here quite often. I own a '98.5 A4 1.8TQTSS

paul

Very interesting article.... This piece of text is nearly word for word what I would have done and been taught to do by the old automotive sages of the 50s and 60s era and perhaps the 70s and 80s to a lesser extent. Having been an mechanic at a Ford dealership in the early 60s I was well versed in the "wisdom" of the time. But in those days it was common to see a car with a trail of blue smoke behind and/or other problems. Now days its not common and furthermore break in periods are just not discussed as much as they used to be nor do a lot of people even read the operating guide that speaks of low speeds for the first 1K miles. All of this makes me wonder if the break in is as important as it used to be. I'm not suggesting that the break in shouldn't be practiced, I definately do exactly (nearly) as your author states. I cringe when dealers take prospective buyers out in a BRAND NEW car (Audi's too) right off the truck and thrash then about. Also when renting cars I have had several brand new ones, these cars are definately not cared for properly. Though I know nobody that adheres to these procedures among my friends etc. and their cars do not seem to be any worse for the wear, whereas (in my opinion) they would have been in big trouble 40yrs ago. Perhaps someone out there that has much more knowledge than me about current materials and engineering knows the real skinny is on this. But its my feeling that though important, its just not that critical anymore.
Paul

JMorrison

Good stuff! Should be required reading---"Break-In" FAQ?

Vance

Modern piston ring design (since the 70s) uses light ring pressures to reduce friction. For good sealing, the top ring is designed so that combustion chamber pressure is allowed behind the ring to press it against the cylinder wall -- some during compression, more during compustion. If you baby the engine during breakin (no full throttle therefore no high pressures) the rings and walls glaze and never seat with one another. There's a long story about a '73 911E that goes with this, but...