Has your 996 or 997 engine had a major rebuild?
Poll: Has your 996 or 997 engine had a major rebuild?
Total Members Polled: 867
Discussion
Stevorocket said:
As a GT3 owner I continue to be impressed with the sheer brilliance of this car over my 4.5 years of ownership - Italy, Hungary, France, Germany, Belgium, Holland, Austria have all fallen to its sword.
Imola, Spa, Monza, Nurburgring, Mas du Clos, Pau, Hungaroring, Oulton, Donington, Goodwood, Silverstone, Cadwell, have all felt the heat of its exhaust fumes!
The emissions on its original cats are so low that it continues to purify the air it breathes.
No failures, no dramas, never stranded.
Awesome.
Sounds like you are enjoying your GT3 to the full!Imola, Spa, Monza, Nurburgring, Mas du Clos, Pau, Hungaroring, Oulton, Donington, Goodwood, Silverstone, Cadwell, have all felt the heat of its exhaust fumes!
The emissions on its original cats are so low that it continues to purify the air it breathes.
No failures, no dramas, never stranded.
Awesome.
But you do understand that your post is not relevant to this thread dont you?
MTR
The new section 5 of our Internet based buyers guide has now been uploaded ref cylinder scoring issues (see www.hartech.org buyers guide). You will need a lot of time and probably a headache pill or two if you want to read the whole lot in one go.
It has been written to inform anyone at any level of relevant knowledge (from a non technical owner to an experienced qualified engineer) - that is interested in the problem of cylinder scoring in 996 and 997 3.6, 3.8 and Cayman S engines - what the many contributory factors are and why.
Briefly it covers why it is easy to design an engine so bullet proof that it never ever goes wrong but it would then be very expensive and heavy as a result. With pressures on profitability, low emissions and higher performance - manufacturers have been under pressure to trim designs, weights, costs, emissions and fuel economy while increasing performance - which inevitably moves their products closer to reliability or longevity limits.
This section gradually explains how some systems that worked OK in air cooled 911's and the 944/968 range had small subtle differences when applied across into the M96 engines that individually seemed insignificant but actually pushed each reliability issue slightly closer towards the limit - but insufficient to cause a problem (in other words pretty well perfectly designed for the needs of the modern World). Many of the changes and weaknesses seem also to concentrate the problem on bank 2 (where most of the failures are).
When the later bigger capacity and more powerful versions were built - instead of changing some of those marginal issues to compensate for the additional heat and loads - it seems that they were either left exactly the same or in one case while moving in the right direction for reducing costs - went entirely in the wrong direction for reliability - resulting in engines running so much closer to that boundary - that some - after ageing and with some wear and tear taking place and after experiencing different driving conditions and styles - simply slip over the boundary and become damaged (usually on bank 2).
The scenario is typical of many other historical engines from different manufacturers that following a capacity or performance increase - search out and find the weak spots in a previously reliable design.
Usually a small but significant modification eventually appears on the market to fix the problem - but more often from smaller specialist organisations (that is presently taking place with these engines).
Because this initial engine range was actually so very well designed to run really close to - but still inside those "safety margins" - the increased performance applied to later models without other supporting alterations - has revealed a complex list of contributory weak spots - each even closer to the limits - such that a particular mix of sometimes different circumstances can push the engine over them.
It is therefore a complex problem requiring lengthy investigation and testing, proving good well founded solutions while exposing some other inadequate ones recently coming to the market.
This 25,000 word section explains each issue with both simple explanations and analogies backed up with technical and scientific facts so anyone should be able to grasp the salient points and realise that there are several issues to consider and several modifications that are beneficial during a rebuild and not one simple fix. It also includes further new developments that may help owners avoid the problem.
Before readers start with responding with typical criticism – please remember that I don’t need to write this stuff for my benefit (I already understand it) and furthermore if I spent the same amount of time and effort it took to write this section on promoting our business in other advertising or marketing ways – it would certainly result in greater financial rewards. It has been written to inform others about the problem – what we know about it and what we do about it – to prevent misleading alternatives from confusing owners – empowering them to make informed decisions if they need help or advice.
Although many with more experience would not need to read the whole of it to understand what it contains, I do not intend to respond to any criticism unless every word has already been read.
Best regards and happy reading,
It has been written to inform anyone at any level of relevant knowledge (from a non technical owner to an experienced qualified engineer) - that is interested in the problem of cylinder scoring in 996 and 997 3.6, 3.8 and Cayman S engines - what the many contributory factors are and why.
Briefly it covers why it is easy to design an engine so bullet proof that it never ever goes wrong but it would then be very expensive and heavy as a result. With pressures on profitability, low emissions and higher performance - manufacturers have been under pressure to trim designs, weights, costs, emissions and fuel economy while increasing performance - which inevitably moves their products closer to reliability or longevity limits.
This section gradually explains how some systems that worked OK in air cooled 911's and the 944/968 range had small subtle differences when applied across into the M96 engines that individually seemed insignificant but actually pushed each reliability issue slightly closer towards the limit - but insufficient to cause a problem (in other words pretty well perfectly designed for the needs of the modern World). Many of the changes and weaknesses seem also to concentrate the problem on bank 2 (where most of the failures are).
When the later bigger capacity and more powerful versions were built - instead of changing some of those marginal issues to compensate for the additional heat and loads - it seems that they were either left exactly the same or in one case while moving in the right direction for reducing costs - went entirely in the wrong direction for reliability - resulting in engines running so much closer to that boundary - that some - after ageing and with some wear and tear taking place and after experiencing different driving conditions and styles - simply slip over the boundary and become damaged (usually on bank 2).
The scenario is typical of many other historical engines from different manufacturers that following a capacity or performance increase - search out and find the weak spots in a previously reliable design.
Usually a small but significant modification eventually appears on the market to fix the problem - but more often from smaller specialist organisations (that is presently taking place with these engines).
Because this initial engine range was actually so very well designed to run really close to - but still inside those "safety margins" - the increased performance applied to later models without other supporting alterations - has revealed a complex list of contributory weak spots - each even closer to the limits - such that a particular mix of sometimes different circumstances can push the engine over them.
It is therefore a complex problem requiring lengthy investigation and testing, proving good well founded solutions while exposing some other inadequate ones recently coming to the market.
This 25,000 word section explains each issue with both simple explanations and analogies backed up with technical and scientific facts so anyone should be able to grasp the salient points and realise that there are several issues to consider and several modifications that are beneficial during a rebuild and not one simple fix. It also includes further new developments that may help owners avoid the problem.
Before readers start with responding with typical criticism – please remember that I don’t need to write this stuff for my benefit (I already understand it) and furthermore if I spent the same amount of time and effort it took to write this section on promoting our business in other advertising or marketing ways – it would certainly result in greater financial rewards. It has been written to inform others about the problem – what we know about it and what we do about it – to prevent misleading alternatives from confusing owners – empowering them to make informed decisions if they need help or advice.
Although many with more experience would not need to read the whole of it to understand what it contains, I do not intend to respond to any criticism unless every word has already been read.
Best regards and happy reading,
HoHoHo said:
Sorry Baz.
As you know, the devil is in the detail......
Why should we believe anything you write about a complicated engine when you can't get you opening and closing dates over Christmas correct on your website?
Opening 8.30 Tuesday 2/11
Closed for 11 months, silly Ho! (I didn't wanna say anything when ai saw it...)As you know, the devil is in the detail......
Why should we believe anything you write about a complicated engine when you can't get you opening and closing dates over Christmas correct on your website?
Opening 8.30 Tuesday 2/11
Edited by HoHoHo on Friday 23 December 19:49
Thanks for pointing that out - after writing that section I could do with a break (but not that long). Mind you - we know that Porsche owners from all over the UK and abroad - go to extraordinary lengths to reach us - but we wouldn't want them to hire the "back to the future car" to do so!
We actually do not manage our own web site - and anything like that is handled by sub-contractors (so not strictly our fault) but they didn't mess with the section 5 they uploaded for us - so anything on there you can blame me for - although I am sure it will be full of spelling and grammatical errors (so plenty to go at) - but please confine future criticisms to the serious technical issues it is trying to inform people about.
Unfortunately - among my many failings are that I am not a technical writer (well I guess you have worked that out already!) nor a marketing expert - just an engineer with the experience and ability to analyse problems, the resources to test and try things, the equipment to produce good solutions and the capacity to repair faulty engines very well indeed.
When I combine that with a natural disposition to inform and help unfortunate owners when they need good honest advice through a medium fraught with difficulties and full of miss-information - you end up with a massive effort to put it all down in writing - that - for me - was very difficult and time consuming.
At least your response has demonstrated exactly what I was referring to in the section about the difficulties of the Internet and how people cannot wait to criticise with irrelevant or inaccurate responses - which for me has justified the lengths I went to in trying to explain everything - and in so doing has made my Christmas.
In the true spirit of Yuletide - have a happy picky Christmas.
Baz
We actually do not manage our own web site - and anything like that is handled by sub-contractors (so not strictly our fault) but they didn't mess with the section 5 they uploaded for us - so anything on there you can blame me for - although I am sure it will be full of spelling and grammatical errors (so plenty to go at) - but please confine future criticisms to the serious technical issues it is trying to inform people about.
Unfortunately - among my many failings are that I am not a technical writer (well I guess you have worked that out already!) nor a marketing expert - just an engineer with the experience and ability to analyse problems, the resources to test and try things, the equipment to produce good solutions and the capacity to repair faulty engines very well indeed.
When I combine that with a natural disposition to inform and help unfortunate owners when they need good honest advice through a medium fraught with difficulties and full of miss-information - you end up with a massive effort to put it all down in writing - that - for me - was very difficult and time consuming.
At least your response has demonstrated exactly what I was referring to in the section about the difficulties of the Internet and how people cannot wait to criticise with irrelevant or inaccurate responses - which for me has justified the lengths I went to in trying to explain everything - and in so doing has made my Christmas.
In the true spirit of Yuletide - have a happy picky Christmas.
Baz
hartech said:
Thanks for pointing that out - after writing that section I could do with a break (but not that long). Mind you - we know that Porsche owners from all over the UK and abroad - go to extraordinary lengths to reach us - but we wouldn't want them to hire the "back to the future car" to do so!
We actually do not manage our own web site - and anything like that is handled by sub-contractors (so not strictly our fault) but they didn't mess with the section 5 they uploaded for us - so anything on there you can blame me for - although I am sure it will be full of spelling and grammatical errors (so plenty to go at) - but please confine future criticisms to the serious technical issues it is trying to inform people about.
Unfortunately - among my many failings are that I am not a technical writer (well I guess you have worked that out already!) nor a marketing expert - just an engineer with the experience and ability to analyse problems, the resources to test and try things, the equipment to produce good solutions and the capacity to repair faulty engines very well indeed.
When I combine that with a natural disposition to inform and help unfortunate owners when they need good honest advice through a medium fraught with difficulties and full of miss-information - you end up with a massive effort to put it all down in writing - that - for me - was very difficult and time consuming.
At least your response has demonstrated exactly what I was referring to in the section about the difficulties of the Internet and how people cannot wait to criticise with irrelevant or inaccurate responses - which for me has justified the lengths I went to in trying to explain everything - and in so doing has made my Christmas.
In the true spirit of Yuletide - have a happy picky Christmas.
Baz
Hi BazWe actually do not manage our own web site - and anything like that is handled by sub-contractors (so not strictly our fault) but they didn't mess with the section 5 they uploaded for us - so anything on there you can blame me for - although I am sure it will be full of spelling and grammatical errors (so plenty to go at) - but please confine future criticisms to the serious technical issues it is trying to inform people about.
Unfortunately - among my many failings are that I am not a technical writer (well I guess you have worked that out already!) nor a marketing expert - just an engineer with the experience and ability to analyse problems, the resources to test and try things, the equipment to produce good solutions and the capacity to repair faulty engines very well indeed.
When I combine that with a natural disposition to inform and help unfortunate owners when they need good honest advice through a medium fraught with difficulties and full of miss-information - you end up with a massive effort to put it all down in writing - that - for me - was very difficult and time consuming.
At least your response has demonstrated exactly what I was referring to in the section about the difficulties of the Internet and how people cannot wait to criticise with irrelevant or inaccurate responses - which for me has justified the lengths I went to in trying to explain everything - and in so doing has made my Christmas.
In the true spirit of Yuletide - have a happy picky Christmas.
Baz
Bit of light hearted wine fuelled banter (I deleted it pretty much immediately having realised it may not be as funny as I thought at the time, not quick enough obviously!).
I've read some of the information and it makes for nteresting reading - thanks for the effort (as you suggested it is a long piece and will be read over more than one session!).
No offence intended and Happy Christmas
I just picked my 2001 996 up after having a modified intermediate shaft bearing fitted. The bugger has come out clean and shiny but there was oil seepage around the housing which is why I had the work done. Not sure if that statement is technically correct as I know the IMS bearing is dry as opposed to the modified one. The RMS was also changed as that was leaking as well.
I'm not sure if this means my engine would have been fine left alone or if it was disaster waiting to happen. But now I can relax until the next bout of scaremongering, I am not even researching scored bores or D chunks.
I have had the car 13 months and after I collected my 'bargain' last Novemebr I was advised that it needed a new cylinder head
which was duly fitted but made it something less of a bargain.
All this means is that I do not know what option to select on the vote as neither job can be classified as a major rebuild but were an expensvie PITA.
BTW, I just love the car, especially since I had the Sports Exhaust fitted at the same time.
I'm not sure if this means my engine would have been fine left alone or if it was disaster waiting to happen. But now I can relax until the next bout of scaremongering, I am not even researching scored bores or D chunks.
I have had the car 13 months and after I collected my 'bargain' last Novemebr I was advised that it needed a new cylinder head
which was duly fitted but made it something less of a bargain.All this means is that I do not know what option to select on the vote as neither job can be classified as a major rebuild but were an expensvie PITA.
BTW, I just love the car, especially since I had the Sports Exhaust fitted at the same time.
theres no d chunk failures in this survey ......eh
Autofarm have had a good run of bizz out of that one
does this mean its not happening??
how truthful are people being about the level of problems?
if you owned a 997.1 on an 04/5 plate and wanted to get rid would you add to this survey?
if you wanted the price of your 997 not to drop would you add to the 148?
just a thought
Autofarm have had a good run of bizz out of that one
does this mean its not happening??
how truthful are people being about the level of problems?
if you owned a 997.1 on an 04/5 plate and wanted to get rid would you add to this survey?
if you wanted the price of your 997 not to drop would you add to the 148?
just a thought
uktrailmonster said:
Probably means that most people don't have the faintest idea what 'd chunk' means. Myself included ???
Its when a crack forms in the liner this crack travels over a period of time usually (I dont know why help Baz) forming a kind of "D" shape once the crack reaches the bottom edge of the liner said "D" shaped chunk of liner drops off into the bowels of the engine,which then attempts to consume it whith much noise and oil and tears from the owner!Very nasty indeed
Gary11 said:
Its when a crack forms in the liner this crack travels over a period of time usually (I dont know why help Baz) forming a kind of "D" shape once the crack reaches the bottom edge of the liner said "D" shaped chunk of liner drops off into the bowels of the engine,which then attempts to consume it whith much noise and oil and tears from the owner!
Very nasty indeed
From reading Hartechs hugely informaive guide its due to the cylinders going oval gradually leading to the non too flexible liner spltting then finally falling off in a nice d shape. Very nasty indeed
Whilst i think about it Baz is it worth getting a Boroscope and checking for cracks now and then. idea being that you book it in to get rebuilt before said chunk ends up in bowls as presume it would save you a d chunk of cash? Or does crack to chunk happen too quickly to be likley to catch it? Mines heading towards 120k without rebuild of nice warmed up motorway miles so trying to weigh up when to send it to you.
Hi Dumpy, sorry but despite seeing and repairing loads of cracked and "D" chunked cylinders - it is difficult to know the exact sequence of all the vents.
If it is a crack it usually mainifests itself as pressurising the cylinder block and running hot - possibly a slight misfire first - but the problem is that if we do not see the "D" chunk cars until the "D" chunk has fallen out - there is no real way of knowing if they experienced the others sypmtoms first. Perhaps they don't want to admit it or perhaps they are not mechanically sympathetic and kept driving until if totally failed.
I think they must crack first though - we have had some come in with "crack" symptoms that if we just lightly tap the cylinder - a "D" chunk piece then falls out.
The failure is through metal fatigue. Every 2 revs each cylinder on the thrust side is stressed by the piston pushing against it on the firing stroke in order to push the crankshaft round - plus there is also "hoop" stress as a result of the pressure from combustion pushing outwards on the whole cylinder surface.
Most metal fatigue in steels can have a fairly reliable number of stress reversals leading to failure (if the component has been designed too weak) or if it is made a little bigger - may literally last forever (as the amount of distortion never reaches enough movement to initiate a crack).
However both aluminium alloys (and I believe composites like the Lokasil cast in liner) still have a predictable number of regualr stress reversals to failure and even if you make them a little thicker/bigger - it only really prolongs the fatigue life some more - but never infinitely.
This is why I find it odd that the later engines had thinner cylinder walls than the earlier ones (that were smaller engines and therefore produced less cylinder wall stress). I don't want to speculate too much as to why - draw your own conclusions).
It is the result of this knowledge and seeing engines with cracks from as low as sub 40K up to 150K that makes me conclude that they will all do it eventually (the difference in mileage having something to do with slight variations in castings, liners and the way they are warmed up and driven.
Certainly slower warming up will prolong life and so will less aggressive driving - but then they are sports cars and should be designed to take it.
The earlier 944 turbos also had an "open deck" cylinder design but no weaker liner and the whole cylinder was made in Alusil (which is much stronger) and in normal use they last almost for ever without much distortion or cracking.
However if they are very highly tuned for racing - even they then start to distort the cylinders (leading to abraisons where the cylinder meets the head gasket) and eventually crack.
If I know this I am guessing Porsche must do and then slots cut out of the M96 head gasket (to allow some movement without breaking the seal) suggest they did - but (like the std 944 turbo) the engines were OK with the thicker cylinders in the 2.5, 2.7 and 3.2 Boxster versions - it seems that a risk was taken that they would still be OK (or there may be a more cynical explanation).
It is a real shame because a simple ring in the top would have stopped the problem (as we fit to our rebuilt engines as an option) and would have cost peanuts to do - but I get the feeling that a battle between engineers and peanut counters decided issues like this - not always in the engineers favour.
Baz
If it is a crack it usually mainifests itself as pressurising the cylinder block and running hot - possibly a slight misfire first - but the problem is that if we do not see the "D" chunk cars until the "D" chunk has fallen out - there is no real way of knowing if they experienced the others sypmtoms first. Perhaps they don't want to admit it or perhaps they are not mechanically sympathetic and kept driving until if totally failed.
I think they must crack first though - we have had some come in with "crack" symptoms that if we just lightly tap the cylinder - a "D" chunk piece then falls out.
The failure is through metal fatigue. Every 2 revs each cylinder on the thrust side is stressed by the piston pushing against it on the firing stroke in order to push the crankshaft round - plus there is also "hoop" stress as a result of the pressure from combustion pushing outwards on the whole cylinder surface.
Most metal fatigue in steels can have a fairly reliable number of stress reversals leading to failure (if the component has been designed too weak) or if it is made a little bigger - may literally last forever (as the amount of distortion never reaches enough movement to initiate a crack).
However both aluminium alloys (and I believe composites like the Lokasil cast in liner) still have a predictable number of regualr stress reversals to failure and even if you make them a little thicker/bigger - it only really prolongs the fatigue life some more - but never infinitely.
This is why I find it odd that the later engines had thinner cylinder walls than the earlier ones (that were smaller engines and therefore produced less cylinder wall stress). I don't want to speculate too much as to why - draw your own conclusions).
It is the result of this knowledge and seeing engines with cracks from as low as sub 40K up to 150K that makes me conclude that they will all do it eventually (the difference in mileage having something to do with slight variations in castings, liners and the way they are warmed up and driven.
Certainly slower warming up will prolong life and so will less aggressive driving - but then they are sports cars and should be designed to take it.
The earlier 944 turbos also had an "open deck" cylinder design but no weaker liner and the whole cylinder was made in Alusil (which is much stronger) and in normal use they last almost for ever without much distortion or cracking.
However if they are very highly tuned for racing - even they then start to distort the cylinders (leading to abraisons where the cylinder meets the head gasket) and eventually crack.
If I know this I am guessing Porsche must do and then slots cut out of the M96 head gasket (to allow some movement without breaking the seal) suggest they did - but (like the std 944 turbo) the engines were OK with the thicker cylinders in the 2.5, 2.7 and 3.2 Boxster versions - it seems that a risk was taken that they would still be OK (or there may be a more cynical explanation).
It is a real shame because a simple ring in the top would have stopped the problem (as we fit to our rebuilt engines as an option) and would have cost peanuts to do - but I get the feeling that a battle between engineers and peanut counters decided issues like this - not always in the engineers favour.
Baz
ok lets ask Baz if he wouldn't mind.
how many d chunks have you fixed ?
how many scored bores have you fixed ?
How many IMS?
How accurate do you think this survey is with none in the d chunk section?
Do you think Porsche should be fixing low mileage engines ?
How bad is it for there image?
Do you see this happening more and more ?
how many d chunks have you fixed ?
how many scored bores have you fixed ?
How many IMS?
How accurate do you think this survey is with none in the d chunk section?
Do you think Porsche should be fixing low mileage engines ?
How bad is it for there image?
Do you see this happening more and more ?
Just a balancing post,-- Just sold my 03 C4S after 3 years and 20,000 miles of trouble free oil leak free and mostly warranty free miles, not only that I was the 6th owner.
Traded in for a 2 owner 55 plate 997 C2S as new with 21,000 on the clock, intending to keep for 3/4 years so has 2 yr OPC warranty included when I will be on the lookout for a GTS at sensible money.
Traded in for a 2 owner 55 plate 997 C2S as new with 21,000 on the clock, intending to keep for 3/4 years so has 2 yr OPC warranty included when I will be on the lookout for a GTS at sensible money.
Gassing Station | 911/Carrera GT | Top of Page | What's New | My Stuff