"Break in" period
11-25-2010, 03:37 PM
#21
6th Gear Member
Join Date: Feb 2007
Location: state of confusion
Posts: 7,635
In this case, it's not about being able to withstand the heat. That's the ring engineer/designer's job to properly select.
It's that the rings will expand circumferentially more and faster than the block can because they heat up faster and to a much higher temperature. If ring expansion (circumferentially) tries to exceed block expansion (ditto) plus the ring end gap (which is really a circumferential measurement already), bad things tend to follow.
Norm
It's that the rings will expand circumferentially more and faster than the block can because they heat up faster and to a much higher temperature. If ring expansion (circumferentially) tries to exceed block expansion (ditto) plus the ring end gap (which is really a circumferential measurement already), bad things tend to follow.
Norm
11-25-2010, 11:12 PM
#22
That makes sense. And based on the engineers being the one's to choose the appropriate materials, I presume the Ford guys chose the proper alloys for the the pistons for engine RPMs above 7K and also some engine temp above the spec max temp (for safety factor reasons).
As such, I also presume that the Coyote can be run up to 4-5K RPM shortly after the break-in without any ill-effects.
I did a quick search in the net for more info about piston rings and I found this one from Fed Mogul, which includes the materials performance info of their rings. I am however not sure if those alloys are industry standard or just the rings they sell.
http://www.federalmogul.com/korihand...section_41.htm
I am led to believe that the rings might expand less than we are thinking even for the heat they are taking, but yes, they will still expand more than the diameter of the cylinder to get the seal that they are supposed to provide. It's just that I don't think they will over-expand to start inducing inappropriate frictional forces that would be detrimental to the engine and/or engine performance, unless of course more heat is than what the Ford engineers designed them for gets into the rings.
As such, I also presume that the Coyote can be run up to 4-5K RPM shortly after the break-in without any ill-effects.
I did a quick search in the net for more info about piston rings and I found this one from Fed Mogul, which includes the materials performance info of their rings. I am however not sure if those alloys are industry standard or just the rings they sell.
http://www.federalmogul.com/korihand...section_41.htm
I am led to believe that the rings might expand less than we are thinking even for the heat they are taking, but yes, they will still expand more than the diameter of the cylinder to get the seal that they are supposed to provide. It's just that I don't think they will over-expand to start inducing inappropriate frictional forces that would be detrimental to the engine and/or engine performance, unless of course more heat is than what the Ford engineers designed them for gets into the rings.
11-26-2010, 08:04 AM
#23
6th Gear Member
Join Date: Feb 2007
Location: state of confusion
Posts: 7,635
The details of material selection as far as ring durability in and of itself should be pretty well nailed down by now. Properly built race engines don't fail very often with this as a cause, nor do most 'normal' cars' engines.
It's the dimensional details that are more cause for concern. Anything that is fabricated is subject to tolerance, and it is entirely possible to end up with a ring that's a little past tolerance on the 'long' side. That's what you don't know unless you are the guy who assembled the engine or were at least in communication with the guy who did. We ARE dealing with dimensional differences down in the few-thousandths-of-an-inch range . . .
Norm
It's the dimensional details that are more cause for concern. Anything that is fabricated is subject to tolerance, and it is entirely possible to end up with a ring that's a little past tolerance on the 'long' side. That's what you don't know unless you are the guy who assembled the engine or were at least in communication with the guy who did. We ARE dealing with dimensional differences down in the few-thousandths-of-an-inch range . . .
Norm
11-26-2010, 10:20 AM
#24
True that, and my mind is beginning to swim with thoughts on this.
I have no clue what the acceptable designed operating diameters are supposed to be for the piston rings and the cylinder block.
No doubt the cylinder liner will be a material that is more resistant to thermal strain than the aluminum block, and with the benefit of being cooled as heat is taken away bu the coolant in the block, and the rings don't have that benefit (except for getting some oil getting onto them from the oil holes from the insides of the pistons that go to the piston ring recesses.
On a side note, the '11 Coyote has oil squirters that shoot oil onto the insides of the pistons to help promote this. I do not know if the 4.6L and the earlier 5.4L engines have these piston squirters.
My only assumption here is that even for rings that are slightly over designed spec diameters, even it it is only 0.005 in above the blue print diameter, the break-in process will wear down that errant ring to the proper diameter while at the same time the cross-hatching of the cylinder liner is also being worn down to create the proper seal.
All the while, the thermal expansion of the rings are forcing them against the liners to accomplish this.
(I'm just basically saying this for the other readers, you and I already know this.)
Since I have no clue what the designed expansion diameters are supposed to be and what the designed heats these things are supposed to take, I therefore have absolutely no clue just how much is too much.
The questions that float in my head are Just what are the acceptable thermal expansion tolerances? Is it supposed to be +/- 0.002 in at operating thermal expansion and anything over that tolerance is too much/too little? Likewise for the cylinder liner.
I have no clue what the acceptable designed operating diameters are supposed to be for the piston rings and the cylinder block.
No doubt the cylinder liner will be a material that is more resistant to thermal strain than the aluminum block, and with the benefit of being cooled as heat is taken away bu the coolant in the block, and the rings don't have that benefit (except for getting some oil getting onto them from the oil holes from the insides of the pistons that go to the piston ring recesses.
On a side note, the '11 Coyote has oil squirters that shoot oil onto the insides of the pistons to help promote this. I do not know if the 4.6L and the earlier 5.4L engines have these piston squirters.
My only assumption here is that even for rings that are slightly over designed spec diameters, even it it is only 0.005 in above the blue print diameter, the break-in process will wear down that errant ring to the proper diameter while at the same time the cross-hatching of the cylinder liner is also being worn down to create the proper seal.
All the while, the thermal expansion of the rings are forcing them against the liners to accomplish this.
(I'm just basically saying this for the other readers, you and I already know this.)
Since I have no clue what the designed expansion diameters are supposed to be and what the designed heats these things are supposed to take, I therefore have absolutely no clue just how much is too much.
The questions that float in my head are Just what are the acceptable thermal expansion tolerances? Is it supposed to be +/- 0.002 in at operating thermal expansion and anything over that tolerance is too much/too little? Likewise for the cylinder liner.
11-26-2010, 10:40 AM
#26
You don't have to change it every 3K miles if you are synth and semi-synth oil.
If you are using regular 'ole dinosaur oil form the ground with absolutely no syth blended into it, then yes, change your oil every 3K miles. With synth blends, you can actually go 6-7.5K miles (depending on how hard you drive) and be okay. I presume you drive your car as a daily driver. If it is just a weekend driver, you might consider not buying the most expensive full synth oil (save some money). As a result of not driving it much, it would also take you a long time to reach 3000 miles anyway.
If you are using regular 'ole dinosaur oil form the ground with absolutely no syth blended into it, then yes, change your oil every 3K miles. With synth blends, you can actually go 6-7.5K miles (depending on how hard you drive) and be okay. I presume you drive your car as a daily driver. If it is just a weekend driver, you might consider not buying the most expensive full synth oil (save some money). As a result of not driving it much, it would also take you a long time to reach 3000 miles anyway.
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