Why is No 6 Cylinder the usual piston failure target
- Thread starter Big Bob
- Start date
You sound like you must have had a string of bad luck to even have a hint that one of them might be worse than others. Perhaps the lack of reply is just lack of experience of bad engines...
On your cooling-route question - I'd have thought it would be fairly obvious from looking at the plumbing and the feeling (after a short run from cold) for temperature to work out which is "in" and which is "out".
On your cooling-route question - I'd have thought it would be fairly obvious from looking at the plumbing and the feeling (after a short run from cold) for temperature to work out which is "in" and which is "out".
Big Bob
PCGB Member
No Mark, I have not been sure because of the complex nature of the water jacket etc which is the last cylinder to get the cool water. But if you know please tell me, because from lying under the car its very difficult to know. With normal engine bays when you can look down in comfort I could figure it out.
Thanks Big Bob
Thanks Big Bob
Hi Bob,
I can't help with the knowledge,sorry, but am intrigued to know what you will do with the info if you do indeed find that No6 is the last one down the line. I don't know what and how (and if!) they check the water temp. throughout the engine during development for hot spots? I would have thought it was best not left to chance though!
Cheers Alan
I can't help with the knowledge,sorry, but am intrigued to know what you will do with the info if you do indeed find that No6 is the last one down the line. I don't know what and how (and if!) they check the water temp. throughout the engine during development for hot spots? I would have thought it was best not left to chance though!
Cheers Alan
Big Bob
PCGB Member
Thanks Alan
I relatively new to Porsche ownership, having vowed over 40 years I would never buy one (Very long story on my conversion - match for Saul of Tsarsus!). I started with a 996 carrera 2 in 2007 and bought a 997 GT3 in November 2008.
As I'm now a lot older, and I dont financially need or enjoy the prospect of getting out and getting under as in my youth, I've not studied the Flat 6 engine in great detail because it is not easy to look at. Shame on me I agree.
However from the age of 16 (I'm now 63) I've rebuilt motorcycles, and cars. I've rebuilt many expensive engines for others as well as myself and so picked up a lot of applicable knowledge.
One of the things I've noted with different engine manufacturers is that the last cylinder in the block especially on long engines V8s and Straight 6s and V12s is that the last cylinder runs hotter than the others. As a consequence it is not unusual especially for competition applications on say Jaguar E Types and Aston Martin DB 4/5/6s and Vantages, to run with a grade down in size on the last cylinder piston.
This reduces the risk of piston nip and consequent pick up at high temperature and load and the next part of failure where the rings snag and break and score up bores leading to a full failure and a major engine repair bill.
Now on another UK Porsche Forum it seems that No 6 Bore on the 997 has a higher reported incidence of piston pick up and ring failure. If Number 6 is the last Cylinder to get water, this might be part of the reason. If the even bank of cylinders gets the water last this might be why Bore 4 also seems to be the next one prevalent to scoreing and pick up.
If that is not the only reason then it must be a lubrication issue as well. On V8 Astons the no 8 conrod has a small drilling to supply a regular squiret of oil from the big end bearing onto the thrust face of the piston bore too.
Anyway just trying to think through issues from the armchair that might point to areas of investigation.
Having worked for a major vehicle manufacturer covering engine manufacture as well as all other aspects of vehicle construction, it is normal to have sensoring to pick up hot spots, but the results from protototype development and manufacturing output and tolerance drift later in the product cycle dont always gel over time.
Regards Big Bob
I relatively new to Porsche ownership, having vowed over 40 years I would never buy one (Very long story on my conversion - match for Saul of Tsarsus!). I started with a 996 carrera 2 in 2007 and bought a 997 GT3 in November 2008.
As I'm now a lot older, and I dont financially need or enjoy the prospect of getting out and getting under as in my youth, I've not studied the Flat 6 engine in great detail because it is not easy to look at. Shame on me I agree.
However from the age of 16 (I'm now 63) I've rebuilt motorcycles, and cars. I've rebuilt many expensive engines for others as well as myself and so picked up a lot of applicable knowledge.
One of the things I've noted with different engine manufacturers is that the last cylinder in the block especially on long engines V8s and Straight 6s and V12s is that the last cylinder runs hotter than the others. As a consequence it is not unusual especially for competition applications on say Jaguar E Types and Aston Martin DB 4/5/6s and Vantages, to run with a grade down in size on the last cylinder piston.
This reduces the risk of piston nip and consequent pick up at high temperature and load and the next part of failure where the rings snag and break and score up bores leading to a full failure and a major engine repair bill.
Now on another UK Porsche Forum it seems that No 6 Bore on the 997 has a higher reported incidence of piston pick up and ring failure. If Number 6 is the last Cylinder to get water, this might be part of the reason. If the even bank of cylinders gets the water last this might be why Bore 4 also seems to be the next one prevalent to scoreing and pick up.
If that is not the only reason then it must be a lubrication issue as well. On V8 Astons the no 8 conrod has a small drilling to supply a regular squiret of oil from the big end bearing onto the thrust face of the piston bore too.
Anyway just trying to think through issues from the armchair that might point to areas of investigation.
Having worked for a major vehicle manufacturer covering engine manufacture as well as all other aspects of vehicle construction, it is normal to have sensoring to pick up hot spots, but the results from protototype development and manufacturing output and tolerance drift later in the product cycle dont always gel over time.
Regards Big Bob
Have you tried asking on:
http://www.renntech.org/forums/index.php?showforum=53
I have always found the guys here to be very knowledgable
http://www.renntech.org/forums/index.php?showforum=53
I have always found the guys here to be very knowledgable
garyw
Moderator
Have to agree that renntech is the tech knowledge base or perhaps a UK indy whom do the engine rebuilds.
I unfortunately have no knowledge of which cylinder is in line for the water cooling last but I am aware that it does seem to be number 6 cylinder thats is showing the scoring and failures.
Again the numbers as a percentage is not high but appreciate that if its your engine with a failure then even 0.1% is to high
garyw
I unfortunately have no knowledge of which cylinder is in line for the water cooling last but I am aware that it does seem to be number 6 cylinder thats is showing the scoring and failures.
Again the numbers as a percentage is not high but appreciate that if its your engine with a failure then even 0.1% is to high
garyw
Not at-all, and I haven't a clue. Just that, if I had car in front of me and was faced with same question, and if it's possible to get a hand to the point where the cooling pipes enter/exit, I'd have a feel for a temperature difference.
Although, now I switch my brain on, I realise that just because the pipes enter/exit at particular points does not necessarily tell you much about what happens inside the jacket... be interesting to see a diagram.
Big Bob
PCGB Member
Thanks guys for the helpful suggestions and added enquiry resources, I'll get onto it.
By the way I'm not on a witch hunt, but I would like to know why, as the problem has the potential of damaging Porsches reputation, and ultimately the sale value of of affected 997 vehicles, which has already taken a hit through our straightened financial conditions in Blighty and the rest of the world.[8|] .
It may only be a very small percentage, but when its you its uncomfortable, and as Porsche owners on average are low mileage users, then this type of failure is more likely to strike after a couple of years when the Extended Warranty is relatively very expensive too[
]!
Big Bob[]
By the way I'm not on a witch hunt, but I would like to know why, as the problem has the potential of damaging Porsches reputation, and ultimately the sale value of of affected 997 vehicles, which has already taken a hit through our straightened financial conditions in Blighty and the rest of the world.[8|] .
It may only be a very small percentage, but when its you its uncomfortable, and as Porsche owners on average are low mileage users, then this type of failure is more likely to strike after a couple of years when the Extended Warranty is relatively very expensive too[
]!Big Bob[
]
Bob, if you are still looking for an answer this might help.
While browsing through my files this morning I came across a pdf version of the 997 tech manual (E_997_KATALOG.pdf, on-line version available here: https://techinfo.porsche.com/techinfo/VFModuleManager?Type=MainFrameSet), this is an extract from the water cooling section: In case the resolution is too low the supply side is the pipe labelled 1 at the top of the diagram, 2 is the return at the bottom.
While browsing through my files this morning I came across a pdf version of the 997 tech manual (E_997_KATALOG.pdf, on-line version available here: https://techinfo.porsche.com/techinfo/VFModuleManager?Type=MainFrameSet), this is an extract from the water cooling section: In case the resolution is too low the supply side is the pipe labelled 1 at the top of the diagram, 2 is the return at the bottom.
Big Bob
PCGB Member
Thanks for that Allan. I've just had an arthroscopy on my left knee which has made sitting at the computer a bit painful for doing a lot of research. What Ive got to figure out is the waterflow throught the internal crankcase and cylinder head water jackets, to establish which cylinder get the water last or to put it another way ends up with the hotest water before it returns to the rads for recooling.
On Total 991.com, there is one guy who has just been told by Porsche UK that they recognise that the failure of his No 6 Cylinder could not be avoided and it was not his fault , being an engine component problem, but they will not contibute a cent to the engine replacement. Apparently the OPC where he had the car has had 3 other 997 engines replaced for the same fault!
Regards Big Bob
On Total 991.com, there is one guy who has just been told by Porsche UK that they recognise that the failure of his No 6 Cylinder could not be avoided and it was not his fault , being an engine component problem, but they will not contibute a cent to the engine replacement. Apparently the OPC where he had the car has had 3 other 997 engines replaced for the same fault!
Regards Big Bob
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