Good video on engine break in, including the usefulness of bearing break in

[oceansize]

A decade ago on M3forum, I did a poll— and there was a strong correlation between breaking in the engine per BMW’s spec and not burning oil (and the inverse— going hard from day 1 and oil burning).

I've got a 104k on my car and I don't burn a drop of oil and I suspect its because the first owner of the car was a woman who puttered around town in it which would make sense if what you say has truth. I don't doubt there is some measure.

[Obioban]

I've got a 104k on my car and I don't burn a drop of oil and I suspect its because the first owner of the car was a woman who puttered around town in it which would make sense if what you say has truth. I don't doubt there is some measure.

Yeah, I don’t burn a drop at 16X,XXX miles. I drive it HARD, but broke it in per factory spec and do let it warm up before getting on it.

[cobra]

A decade ago on M3forum, I did a poll— and there was a strong correlation between breaking in the engine per BMW’s spec and not burning oil (and the inverse— going hard from day 1 and oil burning).

I believe it, I bet there is also a correlation between people who break in a car hard and also continue to drive it hard on a regular basis. I think more time spent at elevated temperatures and RPM's will tend to lose more oil - either past the rings or to evaporation.

I think the S54 in general is not known for burning oil, compared to the M54 for example. The M54 had weird low tension rings that wore out and burned copious amounts of oil over 80k miles. I can't speak to the break in on my M3 since it was purchased used, but it also doesn't burn any oil. Meanwhile, my BMW motorcycle which I did purchase brand new, burns oil. I broke it in very carefully, fluctuating RPMs and load, never revving it up too high, etc. Luck of the draw?

[jet_dogg]

I've got a 104k on my car and I don't burn a drop of oil and I suspect its because the first owner of the car was a woman who puttered around town in it which would make sense if what you say has truth. I don't doubt there is some measure.

My car used to see multiple redline trips a day in the first half of its life as a daily and I've never burned a drop as well.

[digger]

A combustion chamber produces well over 1000psi. That force is concentrated through a rod to the crankshaft. There's a few thousands pounds of pressure there.

Think about what's between the rod and the crank. A rod bearing and oil. If the Bearing touches the journal, you have a very bad day. The highest stressed part of an engine are the rods and the bearings. What makes the need a break in is the slight manufacturing differences between the bearing and the journal. The surfaces will need to wear together to achieve and even flow of oil in such a high stress environment. This also produces less friction and heat.

Heat and contracting may also settle everything in. These clearances can't be felt or seen. They going subtle but if you what, what the engineers have deemed proper wear, stick the designers' recommendations rather than anecdotal nonsense. You may get perfectly machined bearings and a break in is irrelevant. You may not.

I had a C8 lockup while I driving it at 602 miles because the break-in procedure wasn't followed. Some old guy owned it. He was from the villages here in FL. The tires were already almost heat cycled. Rod bearings welded themselves to the crank.

They don't just come up with some random number. There at test cars that get driven and torn apart afterwards to examine everything. They take the time to verify the practical application. The safe number is 1200. Ideally all the parts in every engine should be worn in. It's a very safe number for the masses. One engine may need 762 miles and another 1051 miles. Rod bearings are part of that running-in as it is called by BMW.

The rods are not the most highly stressed part of an engine and that's why the rod itself rarely fails. The bearings shells are also quite soft so they dont see too much stress or they get squashed/smooshed. You see this on high performance engines with ultra-high cylinder pressures or poor tuning (lots of knock) and they use stronger materials to alleviate but these are less forgiving. They also use newer materials for the stop start nonsense as that hammers the bearings.

I highly doubt the C8 locked up its bearings because of lack of break-in , catastrophic failure like that was doomed from the start either the parts were not of suitable quality/spec/size or installation error, oil pump or other oil delivery issue etc.

you only need to look at the break-in procedure to understand these restriction actually do not stop the bearings from being loaded heavily at all. highest loads are from combustion pressure and even at medium throttle at 2-5k rpm generates more force than revving to redline. At ITB engine can be at effective WOT at 50% throttle position or less at low rpm.

[digger]

It seems some people would rather be sorry than safe, just let them be.

nothing wrong with that for bearings, for other things it can be an issue as things need to see moderate loads and this doesn't mean rev the crap out of it it means cylinder pressure

[Tbonem3]

We already know this to be unnec. Changing the oil+filter after an arbitrary amount of miles makes more sense to me than babying the car for an arbitrary amount of miles, though.

[E46 M3]

Thought of this thread when I heard the new Mustang has remote cold start rev that you can hit 5k.

[Arith2]

The rods are not the most highly stressed part of an engine and that's why the rod itself rarely fails. The bearings shells are also quite soft so they dont see too much stress or they get squashed/smooshed. You see this on high performance engines with ultra-high cylinder pressures or poor tuning (lots of knock) and they use stronger materials to alleviate but these are less forgiving. They also use newer materials for the stop start nonsense as that hammers the bearings.

I highly doubt the C8 locked up its bearings because of lack of break-in , catastrophic failure like that was doomed from the start either the parts were not of suitable quality/spec/size or installation error, oil pump or other oil delivery issue etc.

you only need to look at the break-in procedure to understand these restriction actually do not stop the bearings from being loaded heavily at all. highest loads are from combustion pressure and even at medium throttle at 2-5k rpm generates more force than revving to redline. At ITB engine can be at effective WOT at 50% throttle position or less at low rpm.

The rods are definitely the most stressed part of the engine. That's why they over-engineered for engines so often. Think of the pressure in the combustion chamber and the suface area of the piston. It's must larger than the rod. It then shoves this very narrow rod connected by the wrist pin which is also small. The velocity change is up to the rod and it changes directions very quickly. The piston is the second most stressed component and the crank is the third. It's irrelevant how often other things fail. The rod and the rod bearing are subjected to thousands of pounds of pressure everytime your engine goes up and down. That's why rod bearings fail so quickly when they fail. It's genuinely impressive engines survive this. When I was in school, it really hit me how much stress these components handle.

Cams barely have any stress on them and they still get a break in. Technically they don't touch the lifters because of oil. It's a short break in due the lack of stress but they still get broken in.

[digger]

The rods are definitely the most stressed part of the engine. That's why they over-engineered for engines so often. Think of the pressure in the combustion chamber and the suface area of the piston. It's must larger than the rod. It then shoves this very narrow rod connected by the wrist pin which is also small. The velocity change is up to the rod and it changes directions very quickly. The piston is the second most stressed component and the crank is the third. It's irrelevant how often other things fail. The rod and the rod bearing are subjected to thousands of pounds of pressure everytime your engine goes up and down. That's why rod bearings fail so quickly when they fail. It's genuinely impressive engines survive this. When I was in school, it really hit me how much stress these components handle.

Cams barely have any stress on them and they still get a break in. Technically they don't touch the lifters because of oil. It's a short break in due the lack of stress but they still get broken in.

I am not sure you actually understand what stressed actually means. Not withstanding whatever definition you are using If parts are over engineered so they rarely fail they are not highly utilised by definition and stresses are sufficiently below the allow stress that would cause a failure whatever failure mode that may be. In absolute stress terms the pistons are made from cast aluminium and run at up to around 300C the stress levels need to be really low to survive so they do not operate at high stress. Rods are more stressed than the pistons but are of better material.

Having personally done a lot of FEA and force calculations for rotating and reciprocating parts bottom edn parts and parts in the valve train i can tell you the rods are really not very stressed, they do see high loads of course but the failure mode of a rod is normally a lubrication issue or bolting issue in a NA engine. The bearings have a a lot of surface area to withstand the loads and that is why failures are so low. but they don't see high stress.

you might want to calculate the hertzian contact stresses on the camshaft one day and rethink whether it is stressed. they dont heat treat cam lobes to >50HRC for nothing and its not just for surface wear as you need to prevent spalling and such sub surface failures due extremely high to contact shear stress. Cams get a breakin because it is a different mode of lubrication (boundary lubrication) and same with pistons ( boundary, mixed and hydrodynamic depending on piston speed through the cycle) due to the high contact stresses there is a relatively high risk of premature wear if things are not done correctly with a camshaft. its obviously higher risk on a 2V engine.

[jet_dogg]

hmm

[Arith2]

I am not sure you actually understand what stressed actually means. Not withstanding whatever definition you are using If parts are over engineered so they rarely fail they are not highly utilised by definition and stresses are sufficiently below the allow stress that would cause a failure whatever failure mode that may be. In absolute stress terms the pistons are made from cast aluminium and run at up to around 300C the stress levels need to be really low to survive so they do not operate at high stress. Rods are more stressed than the pistons but are of better material.

Having personally done a lot of FEA and force calculations for rotating and reciprocating parts bottom edn parts and parts in the valve train i can tell you the rods are really not very stressed, they do see high loads of course but the failure mode of a rod is normally a lubrication issue or bolting issue in a NA engine. The bearings have a a lot of surface area to withstand the loads and that is why failures are so low. but they don't see high stress.

you might want to calculate the hertzian contact stresses on the camshaft one day and rethink whether it is stressed. they dont heat treat cam lobes to >50HRC for nothing and its not just for surface wear as you need to prevent spalling and such sub surface failures due extremely high to contact shear stress. Cams get a breakin because it is a different mode of lubrication (boundary lubrication) and same with pistons ( boundary, mixed and hydrodynamic depending on piston speed through the cycle) due to the high contact stresses there is a relatively high risk of premature wear if things are not done correctly with a camshaft. its obviously higher risk on a 2V engine.

Stress is newtons over an area applied on an object. I am using this word correctly and it is the exact word I should use. My emphasis is just on how much stress is applied to the components. Less area with the same force equals more stress hence why the rod deals with the most stress overall.

Where do our engines usually see major mechanical failures first? Rod bearings. It's very rare to see a broken cam or a bent rod in a BMW in general. It's rather common to see worn rod bearings. It is absolutely imperative they have proper flow and as even of wear as possible. In the perfect world the engine was designed in on paper, the bearings are perfect and the goal is walk along or as close to the perfect clearance. Thus the break in because in reality, friction exists and so do stress limits. Cams and bearings will both get a break in period if you care about longevity. 20 minutes is reasonable for a race car whereas 1200 miles is not. Not every situation offers the luxury to do things specifically by the book however, if the option is there, do it. Everything has tolerances and nothing is perfect.

[Tbonem3]

Digger, give it up, he's read more textbooks than you.

[digger]

Digger, give it up, he's read more textbooks than you.

Me thinks not if he thinks the pistons are more stressed than the steel parts like crank, cam, valve springs etc

[Arith2]

Me thinks not if he thinks the pistons are more stressed than the steel parts like crank, cam, valve springs etc

I don't want people getting false information about engine mechanics.

I really do enjoy reading textbooks. I sometimes search through AIR and TIS to read up on training manuals and functional descriptions of systems as well. I can imagine there are many others on this forum like this with this mindset. That's the environment we have. Your experience matters, but does it align with the truth? In this case no. I would recommend reading a textbook because even the wrong experience is super invaluable.