997.2 3.8 Engine Failure
02-12-2019, 12:23 PM
#391
Burning Brakes
02-12-2019, 12:56 PM
#392
I don't think that this is a problem that data acquisition will resolve. From my 50 years of machining experience (that has included aluminium castings) not only is there a potential variance in the actual casting but the rate of machining roughing out and even the sharpness of the tool tips used can influence the heat during roughing out and this in turn influences the resting shape before final machining.
The design of the block is indeed a factor.
The M96/7 blocks were open deck construction because they had to be cast at very high pressures requiring steel casting moulds and because of that they needed to be able to be extracted after casting. This is why the cylinders were retained in the centre and left a free top and bottom of the cylinders as open deck. Ironically however this meant they were not very strong (and quite flexible) and they even manufactured the head gasket to allow for the movement of the cylinder at the top by putting cut out sections so t he plastic seal was not broken during the movement. I say ironically because one good aspect of that design was that there were no large section changes near the cylinder tops or bottoms. The downside is that they distort oval in time.
If you pick up a 9A1 block you will see a very large section change between the bottom main bearing shell location and the bottom of the cylinder bore which therefore could theoretically pull at the size and roundness of the bore if it was subjected to age related stress relieving.
Yes decades ago large machine castings were left outside in various conditions to age stress relieve them. There are methods of temperature stress relieving castings that are quicker but any variation in the casting temperature, flow rate and distribution can cause trapped cooling stresses that only slowly influence the final machined sizes over a long period of time and depend mainly on the number of times the engines were warmed up and cooled down and how long they remained at the running temperatures.
I suspect there will just be a small number that experience this fault. It is strange that it is usually an end cylinder that has the most shrinkage, the middle about half that amount and the other end round still suggesting a flow and temperature issue in the original casting. For example it could be that the ones first cast on a shift or last could experience different cooling rates in different areas.
The large main bearing area will stay hot longer after casting than the cylinder bores so will always leave a "pull" stress being restrained by the cylinder and outer casting area inwards towards the centre - which is exactly where we can measure this contraction.
There isn't really an answer because it would be difficult to hone any distortion out as the bottom of the cylinder is blind and there are spray jests in the way.
Perhaps a 4.0 conversion is worth considering if an engine fails in this way?
They are fantastic engines and this fault will either be a very rare and unpredictable one that afflicts a very small number of all of them - or the issue may have been addresses so only early ones suffer. Unfortunately because early ones will probably have also experienced the most heat cycles statistically they would be the most likely to exhibit the fault first either way - so only time will tell which scenario will apply.
I would expect the numbers to be far too small to worry anyone and I don't think there are any steps to reduce the problem except that if some cylinder bores are shrinking in at the bottom, the best way to extend the life of the engine is too thoroughly warm it up before giving it too much throttle - because the piston will seize if it grows bigger than the bore and this is most prevalent on warm up cycles where too much throttle has been applied too soon.
Baz
The design of the block is indeed a factor.
The M96/7 blocks were open deck construction because they had to be cast at very high pressures requiring steel casting moulds and because of that they needed to be able to be extracted after casting. This is why the cylinders were retained in the centre and left a free top and bottom of the cylinders as open deck. Ironically however this meant they were not very strong (and quite flexible) and they even manufactured the head gasket to allow for the movement of the cylinder at the top by putting cut out sections so t he plastic seal was not broken during the movement. I say ironically because one good aspect of that design was that there were no large section changes near the cylinder tops or bottoms. The downside is that they distort oval in time.
If you pick up a 9A1 block you will see a very large section change between the bottom main bearing shell location and the bottom of the cylinder bore which therefore could theoretically pull at the size and roundness of the bore if it was subjected to age related stress relieving.
Yes decades ago large machine castings were left outside in various conditions to age stress relieve them. There are methods of temperature stress relieving castings that are quicker but any variation in the casting temperature, flow rate and distribution can cause trapped cooling stresses that only slowly influence the final machined sizes over a long period of time and depend mainly on the number of times the engines were warmed up and cooled down and how long they remained at the running temperatures.
I suspect there will just be a small number that experience this fault. It is strange that it is usually an end cylinder that has the most shrinkage, the middle about half that amount and the other end round still suggesting a flow and temperature issue in the original casting. For example it could be that the ones first cast on a shift or last could experience different cooling rates in different areas.
The large main bearing area will stay hot longer after casting than the cylinder bores so will always leave a "pull" stress being restrained by the cylinder and outer casting area inwards towards the centre - which is exactly where we can measure this contraction.
There isn't really an answer because it would be difficult to hone any distortion out as the bottom of the cylinder is blind and there are spray jests in the way.
Perhaps a 4.0 conversion is worth considering if an engine fails in this way?
They are fantastic engines and this fault will either be a very rare and unpredictable one that afflicts a very small number of all of them - or the issue may have been addresses so only early ones suffer. Unfortunately because early ones will probably have also experienced the most heat cycles statistically they would be the most likely to exhibit the fault first either way - so only time will tell which scenario will apply.
I would expect the numbers to be far too small to worry anyone and I don't think there are any steps to reduce the problem except that if some cylinder bores are shrinking in at the bottom, the best way to extend the life of the engine is too thoroughly warm it up before giving it too much throttle - because the piston will seize if it grows bigger than the bore and this is most prevalent on warm up cycles where too much throttle has been applied too soon.
Baz
02-12-2019, 12:57 PM
#393
Former Vendor
This failure clearly did not have any “help” from a cold climate, or improper warm up. If it did, the piston would have a competely different wear characteristic.
We have seen that the cold doesn’t just make an impact from an environmental variable, but the winter blend fuels in these areas are the bigger contributing factor. These fuels are much more aggressive in many ways than summer blend fuels, or even winter blend fuels in warmer climates. l can tell you exactly when the fuel formulations change locally- we see the difference as plain as day with data, and output, response at WOT.
We have seen that the cold doesn’t just make an impact from an environmental variable, but the winter blend fuels in these areas are the bigger contributing factor. These fuels are much more aggressive in many ways than summer blend fuels, or even winter blend fuels in warmer climates. l can tell you exactly when the fuel formulations change locally- we see the difference as plain as day with data, and output, response at WOT.
02-12-2019, 01:20 PM
#395
Instructor
I have been following this closely as an owner of a 2009 C4S with 70k miles and it has been very informative. I am about to do an oil change on the car and am thinking of going with the DI40 instead of the Mobil 0W40 I have been using. Should I use the BR30 or BR40 for the 100 miles changeover?
02-12-2019, 03:23 PM
#397
Burning Brakes
02-12-2019, 03:33 PM
#398
Instructor
Originally Posted by Balr14
Say, what part of Menomonee Falls is that in your Avatar image? I must have missed it.
02-12-2019, 03:58 PM
#399
I'm sure sorry about Bronz car, thank you for sharing your experiences.
I dont have a car yet, mainly due to this, it would be devastating, been looking for some time, just not a gambler with higher odds of a large repair, so been looking for newer model but therein lies more expense upfront.
this has however opened up a dialog into issues and hopefully resolutions or preventions.
I'm wondering about the preignition, "still learning here" but isnt there a knock sensor to help with this issue,
also could it be a one time event of bad fuel with a serious enough preignition to start this.
Jake again thank you for sharing your findings, I know it takes considerable effort on your part, which shows your love for these cars.
I dont have a car yet, mainly due to this, it would be devastating, been looking for some time, just not a gambler with higher odds of a large repair, so been looking for newer model but therein lies more expense upfront.
this has however opened up a dialog into issues and hopefully resolutions or preventions.
I'm wondering about the preignition, "still learning here" but isnt there a knock sensor to help with this issue,
also could it be a one time event of bad fuel with a serious enough preignition to start this.
Jake again thank you for sharing your findings, I know it takes considerable effort on your part, which shows your love for these cars.
02-12-2019, 04:37 PM
#400
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The letters (DT) are the series and the number is the weight / grade. DT40 is a 5W/40 and DI40 is a 0W/40, but according to Lake just barely below what would classify it as a 5W/40, so nothing given up to the thinner cold viscosity rating. Those are the right products for the 997s.
Jake had recommended BR30 for the short 100 mile flush but I'm not sure if BR40 would also be OK (maybe in the summer). The BR30 is a 5W/30 and the BR40 a 10W/40 so it might be for the lower cold viscosity rating for better start up flow that he recommended the BR30 be used.
Jake had recommended BR30 for the short 100 mile flush but I'm not sure if BR40 would also be OK (maybe in the summer). The BR30 is a 5W/30 and the BR40 a 10W/40 so it might be for the lower cold viscosity rating for better start up flow that he recommended the BR30 be used.
02-12-2019, 04:49 PM
#401
This failure clearly did not have any “help” from a cold climate, or improper warm up. If it did, the piston would have a competely different wear characteristic.
We have seen that the cold doesn’t just make an impact from an environmental variable, but the winter blend fuels in these areas are the bigger contributing factor. These fuels are much more aggressive in many ways than summer blend fuels, or even winter blend fuels in warmer climates. l can tell you exactly when the fuel formulations change locally- we see the difference as plain as day with data, and output, response at WOT.
We have seen that the cold doesn’t just make an impact from an environmental variable, but the winter blend fuels in these areas are the bigger contributing factor. These fuels are much more aggressive in many ways than summer blend fuels, or even winter blend fuels in warmer climates. l can tell you exactly when the fuel formulations change locally- we see the difference as plain as day with data, and output, response at WOT.
02-12-2019, 05:14 PM
#402
Rennlist Member
I have been following this closely as an owner of a 2009 C4S with 70k miles and it has been very informative. I am about to do an oil change on the car and am thinking of going with the DI40 instead of the Mobil 0W40 I have been using. Should I use the BR30 or BR40 for the 100 miles changeover?
02-12-2019, 06:49 PM
#403
But I do worry a bit regarding those bearings and wonder how much difference DI40 would make compared to M1 0-40. After 120K trouble free miles, do I really want to change habits?
Decisions decisions ...
Last edited by Wayne Smith; 02-12-2019 at 07:11 PM.
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bentrod (12-25-2019)
02-12-2019, 07:01 PM
#404
Since i took ownership of this car over a year ago and 11k miles, ive done oil changes every 3k miles. The car was burning about 1qt of oil per 3k miles. I was using Castrol Edge in the beginning and ive done 2 blackstone oil analysis, which came back excellent. On the last oil change, i decided to use Motul and ive put maybe 1500-2000 miles on the oil since.
I checked the oil level and its perfect, not overfilled nor was it too low. The car developed the sound after it was up to operating temperatures - oil and coolant. I dont think it happened when i started the car or at least i didnt notice it. We did have cold temperatures last night about 28degrees,
The car currently has 76k miles.
I checked the oil level and its perfect, not overfilled nor was it too low. The car developed the sound after it was up to operating temperatures - oil and coolant. I dont think it happened when i started the car or at least i didnt notice it. We did have cold temperatures last night about 28degrees,
The car currently has 76k miles.
Obviously, I know nothing significant about oil and motors and wear and LSPI, but this did raise one of my eyebrows.
02-12-2019, 08:31 PM
#405
Rennlist Member
Castrol vs Motul......very interesting.....to bad there isn’t some kind of standardized test at different temperatures to determine some kind of a wear protection ranking. Although this is only one factor in a multifaceted cause for pistoncoating breakdown and borescoring.
Apparently temperature in this area is one factor so a LTT would seem to be a must so that cooling flow is increased in the block at lower rpms and warm up, as well as a third radiator then possibly. Quality fuel also a must to prevent premature detonation , increased piston heat and cylinder fuel wash. Would the regular use of injector cleaner in the fuel system be a good idea?
Apparently temperature in this area is one factor so a LTT would seem to be a must so that cooling flow is increased in the block at lower rpms and warm up, as well as a third radiator then possibly. Quality fuel also a must to prevent premature detonation , increased piston heat and cylinder fuel wash. Would the regular use of injector cleaner in the fuel system be a good idea?