My new M3 has just arrived...
Discussion
taffyracer said:
I disagree, there is alot of evidence to suggest that working the car hard in the 1st 100miles or so helps dramatically with prodcuing a strong engine
I agree with you, infact i know all the precedures to break in a race engine on the dino etc...I have myself a (low compression) race chevy engine i bought for my '77 vette and the builder (American Speed, the same who builds the engines for the Ultima cars) told me the engine once has been runned in on the dino it does not need any other care apart from avoid hard revving when not fully warmed up....BUT the bmw states to go easy on this M3 engine for at least 1.500 miles...so who's right here? could it be that this very engine needs a special procedure due to its building architecture???panic said:
taffyracer said:
I disagree, there is alot of evidence to suggest that working the car hard in the 1st 100miles or so helps dramatically with prodcuing a strong engine
I agree with you, infact i know all the precedures to break in a race engine on the dino etc...I have myself a (low compression) race chevy engine i bought for my '77 vette and the builder (American Speed, the same who builds the engines for the Ultima cars) told me the engine once has been runned in on the dino it does not need any other care apart from avoid hard revving when not fully warmed up....BUT the bmw states to go easy on this M3 engine for at least 1.500 miles...so who's right here? could it be that this very engine needs a special procedure due to its building architecture???
After all how long can it take.Found this, which seemed to make a lot of sense to me. Some of you guys might think differently??
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 with
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. Embarrassingly, 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.
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 7000 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 at 10,000 miles is getting 29 mpg
overall and consumes no oil at all.
Ben Sloss Database Kernel Hacker Email: ben@versant.com
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 with
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. Embarrassingly, 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.
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 7000 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 at 10,000 miles is getting 29 mpg
overall and consumes no oil at all.
Ben Sloss Database Kernel Hacker Email: ben@versant.com
Macca: your run in statement is very educative because it's a sintesis of the two major theories about this iussue, the one that says 'drive it as if you had stolen the car' (otherwise you won't seal the rings) and the second that states that 'a carefully low rpms drive is a must'...thanks.
djohnson said:
panic said:
I don't want to worry you but if I look really carefully at that photo I can see the ghost of a chap from the 1970s stood by your car.
DJ, the only one who does look like a ghost in the pic is myself, extremely tired after a full day of hard work at the harbour
...there is nothing to worry about.Edited by panic on Friday 1st February 04:53
Thanks for the long and very clear explonation.
I still have a question: When you mention that all the RPM need to be used during breaking in, it seems that you explain that in higher RPM "something" is going further. I do not understand this as I was thinking that the movement of the piston, seals,... is the same and only the speed (in fact frequency) is increased and then more hot, which could be a problem,...
Sorry for my english
I still have a question: When you mention that all the RPM need to be used during breaking in, it seems that you explain that in higher RPM "something" is going further. I do not understand this as I was thinking that the movement of the piston, seals,... is the same and only the speed (in fact frequency) is increased and then more hot, which could be a problem,...
Sorry for my english
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