997 cylinder liners
Discussion
This is a bigger technical area than it seems.
We have long since understood the cause of cylinder liner cracks (and everyone now knows we can replace liners and stabilise exusting bores).
However the seizures on the thrust side of the engines are a relatively new problem. We think we understand the cause but need to carry out some tests to verify our theory.
So we have modified some engines that we have rebuilt and they are all OK - but need to try and find a preventative solution for those that have not yet seized.
To do this we are in the process of carrying out several expensive comparative tests accross the engines to determine coolant temperatures etc at various places - to try and quantify the problem and therefore prove a solution. We think this will become a bigger problem in time and have also invested heavily in two potential remedies both of which have lead times before the product is ready to test.
It will interest me to learn more about the problems others are experiencing and I will keep you informed through this medium of any further developments or test results as and when they occur.
Baz
We have long since understood the cause of cylinder liner cracks (and everyone now knows we can replace liners and stabilise exusting bores).
However the seizures on the thrust side of the engines are a relatively new problem. We think we understand the cause but need to carry out some tests to verify our theory.
So we have modified some engines that we have rebuilt and they are all OK - but need to try and find a preventative solution for those that have not yet seized.
To do this we are in the process of carrying out several expensive comparative tests accross the engines to determine coolant temperatures etc at various places - to try and quantify the problem and therefore prove a solution. We think this will become a bigger problem in time and have also invested heavily in two potential remedies both of which have lead times before the product is ready to test.
It will interest me to learn more about the problems others are experiencing and I will keep you informed through this medium of any further developments or test results as and when they occur.
Baz
Is this the same problem as no 6 piston siezing in the bore, or is it a new problem? Currently running a 2002 996 and looking forward to getting a 997, but these type of stories scare the sh*** out of me. Is the Gt3 a safer bet with the different block?
Edited by jcmr2 on Saturday 2nd October 20:45
Yes the problem I am referring to is exactly that - a piston seizing in the bore. There is no mystery as far as I am concerned and no attempt to hide the causes - just a slow process proving the logical theory and measuring the results of modifications to prove the issue.
However it is not confined to the number 6 cylinder or even the 456 side - but is most often 5 or 6 and we have re-linered and rebuilt several engines.
We think the problem relates to insuffient cylinder lubrication between the piston and the Lokasil bore material becase the pistons only ever seize on the thrust side.
We know that the 456 side (bank 2) should run hotter slightly and also that the cooler coolant is first hitting the thrust side of the liner on the 123 side (bank 1) and unfortunatley the opposite side of the 456 (bank 2) cylinders resulting in the thrust face being hotter on that side.
We also know that the later engines with the later variable camshaft timing system produce more torque and that those with variable lift produce even more torque. Although we have seen isolated cases of a 3.4 seizing on one side - it is rare but it seems more common on the 3.4 Cayman engine, more so on the 3.6 engines and 3.8 engines - whereas earlier engines producing less torque with the same materials etc worked OK).
More torque means greater thrust on the cylinder wall between the piston and the Lokasil and probably also means that drivers rev the engines less high but increase the throtte opening at lower revs (as it is so rewarding performance wise) and therefore run more often with greater thrust face loads than before.
The 3.6 and 3.8 engines also have longer strokes but the same deck height which means shorter con rods and of course this also increases the average thrust loads.
There seems to be therefore a direct correlation between the gadual increase in thrust loads and the incidence of thrust face siezure.
When inspecting the remaining pistons from an engine that has a seized piston or two - it is clear that the PTFE type coating is comming off in places on the pistons that have not yet seized - which increases repair costs. This coating is softer if the surface temperature of the piston is higher and therefore is more likely to initiate the problem than the Lokasil material which is generally a very good lubricating surface.
The old practice of pumping coolant into the cylinder block and allowing it to flow up to the cylinder head meant that cylinder heads always ran hotter than cylinder bores. Japanese motorcycle design (and later cars) gradually changed this to exploit the greater cylinder outer surface area and reduce the amount of coolant in the cylinder and increase the amount in the cylinder head by splitting the feed and controlling the quantity with different feed hole diameters - and then allowing it to join together again on the way to the thermostat or radiator.
This means that it is only the average temperature that is being controlled and not the temperature inside the block where the cylinders are located.
Having calculated the difference in flow rates we are concerned that there is marginally enough coolant in the block and this would explain the results because the thickness and lubricating properties of the oil are reduced as the temperature increases. The amount or proportion of coolant in the block seems not to have been increased as the engine sizes have or the torque been increased - so seems not to have responded to the increased cylinder wall to piston pressure referred to above.
If this is the cause then a standard engine is obviously running very close to an acceptable cylinder wall temperature limit causing just a few to fail but expensive to fix. More importantly - when we repair engines with the other more common older faults - we do something to eliminate or to reduce the causes so the rebuilt engine will not suffer a repeat failure. To do so in this case we must be sure of the cause and measure the adjustments we may make to the coolant flow to check if we have got the improvement right.
So this leads back to engines we have built and that are currently under test fitted with various temperature sensors to establish firstly the temperature split on a standard engine (that is usually running OK) then to compare that with a 997 engine fitted with the same sensors (to see if those critical areas are running hotter) and then to test one that we have altered the flow balance to allow the cylinders to run cooler.
All this needs sevaral cars bought by us for the purpose, engines stripped modified and rebuilt, tests and analysis and is costing us a considerable amount of money (for a small independent Porsche specialist) and unfortunately it is taking a long time. At least we are trying our best and although there are some who would just simply say we are doing it for our own commercial benefit - I can assure you that I can make more by investing in other much more simple work than undertaking this huge project the right way. We are only doing this because we are Porsche specialists, we probably rebuild more engines than anyone else and our whole aim is to look after our customers. To do this we seem cornered because we cannot in all fairness simply rebuild the engines without trying to do something about the cause and so must undertake this project to do it properly.
With most of the weak spots these engines exhibit and the rarety of a failure - most of our priority is to repair and improve engines that have failed. But in this case we feel there is the potential to actually stop it happening before they fail - if our analysis is right and so we are not just concentrating upon what to do to repair and at the same time eliminate the problem but also how to prevent it happening in the first place at a reasonable cost so owners can eliminate the probability at modest cost.
I suppose I do expect to eventually recover the costs through a combination of engine rebuilds and our enhanced reputation etc but it will take several years
and right now we are just trying to work through all the various tests while at the same time we have set in motion the production of some parts we believe will solve the problem for those that have not yet experienced it.
I don't think we deserve any harsh comments because we are doing this - indeed I think we are showing a very responsible and customer orientated attitude to a problem that we did not cause and are actually trying to do something affordable about - when it seems the manufacturer and supplier is not.
Baz
However it is not confined to the number 6 cylinder or even the 456 side - but is most often 5 or 6 and we have re-linered and rebuilt several engines.
We think the problem relates to insuffient cylinder lubrication between the piston and the Lokasil bore material becase the pistons only ever seize on the thrust side.
We know that the 456 side (bank 2) should run hotter slightly and also that the cooler coolant is first hitting the thrust side of the liner on the 123 side (bank 1) and unfortunatley the opposite side of the 456 (bank 2) cylinders resulting in the thrust face being hotter on that side.
We also know that the later engines with the later variable camshaft timing system produce more torque and that those with variable lift produce even more torque. Although we have seen isolated cases of a 3.4 seizing on one side - it is rare but it seems more common on the 3.4 Cayman engine, more so on the 3.6 engines and 3.8 engines - whereas earlier engines producing less torque with the same materials etc worked OK).
More torque means greater thrust on the cylinder wall between the piston and the Lokasil and probably also means that drivers rev the engines less high but increase the throtte opening at lower revs (as it is so rewarding performance wise) and therefore run more often with greater thrust face loads than before.
The 3.6 and 3.8 engines also have longer strokes but the same deck height which means shorter con rods and of course this also increases the average thrust loads.
There seems to be therefore a direct correlation between the gadual increase in thrust loads and the incidence of thrust face siezure.
When inspecting the remaining pistons from an engine that has a seized piston or two - it is clear that the PTFE type coating is comming off in places on the pistons that have not yet seized - which increases repair costs. This coating is softer if the surface temperature of the piston is higher and therefore is more likely to initiate the problem than the Lokasil material which is generally a very good lubricating surface.
The old practice of pumping coolant into the cylinder block and allowing it to flow up to the cylinder head meant that cylinder heads always ran hotter than cylinder bores. Japanese motorcycle design (and later cars) gradually changed this to exploit the greater cylinder outer surface area and reduce the amount of coolant in the cylinder and increase the amount in the cylinder head by splitting the feed and controlling the quantity with different feed hole diameters - and then allowing it to join together again on the way to the thermostat or radiator.
This means that it is only the average temperature that is being controlled and not the temperature inside the block where the cylinders are located.
Having calculated the difference in flow rates we are concerned that there is marginally enough coolant in the block and this would explain the results because the thickness and lubricating properties of the oil are reduced as the temperature increases. The amount or proportion of coolant in the block seems not to have been increased as the engine sizes have or the torque been increased - so seems not to have responded to the increased cylinder wall to piston pressure referred to above.
If this is the cause then a standard engine is obviously running very close to an acceptable cylinder wall temperature limit causing just a few to fail but expensive to fix. More importantly - when we repair engines with the other more common older faults - we do something to eliminate or to reduce the causes so the rebuilt engine will not suffer a repeat failure. To do so in this case we must be sure of the cause and measure the adjustments we may make to the coolant flow to check if we have got the improvement right.
So this leads back to engines we have built and that are currently under test fitted with various temperature sensors to establish firstly the temperature split on a standard engine (that is usually running OK) then to compare that with a 997 engine fitted with the same sensors (to see if those critical areas are running hotter) and then to test one that we have altered the flow balance to allow the cylinders to run cooler.
All this needs sevaral cars bought by us for the purpose, engines stripped modified and rebuilt, tests and analysis and is costing us a considerable amount of money (for a small independent Porsche specialist) and unfortunately it is taking a long time. At least we are trying our best and although there are some who would just simply say we are doing it for our own commercial benefit - I can assure you that I can make more by investing in other much more simple work than undertaking this huge project the right way. We are only doing this because we are Porsche specialists, we probably rebuild more engines than anyone else and our whole aim is to look after our customers. To do this we seem cornered because we cannot in all fairness simply rebuild the engines without trying to do something about the cause and so must undertake this project to do it properly.
With most of the weak spots these engines exhibit and the rarety of a failure - most of our priority is to repair and improve engines that have failed. But in this case we feel there is the potential to actually stop it happening before they fail - if our analysis is right and so we are not just concentrating upon what to do to repair and at the same time eliminate the problem but also how to prevent it happening in the first place at a reasonable cost so owners can eliminate the probability at modest cost.
I suppose I do expect to eventually recover the costs through a combination of engine rebuilds and our enhanced reputation etc but it will take several years
and right now we are just trying to work through all the various tests while at the same time we have set in motion the production of some parts we believe will solve the problem for those that have not yet experienced it.
I don't think we deserve any harsh comments because we are doing this - indeed I think we are showing a very responsible and customer orientated attitude to a problem that we did not cause and are actually trying to do something affordable about - when it seems the manufacturer and supplier is not.
Baz
From this initial question "How many of you have problems or have had with your 997 cylinder liners? we need to form a register and join together to get some action or publicity" - I fail to see how a business that specifically repairs the problem and re-fits liners - and their experiences and technical issues are not valuable and frankly I am appalled at the dismissive response to my efforts to help. Obviously there is some hidden agenda that I am not privvy to yet and for some reason - me trying to help is putting a spanner in the plans - so to speak.
However may I make it clear that it is not the role of an initiator to a forum topic to dictate who may and who may not answer nor what content they may or may not feel is appropriate.
If you want specific responses than have the good grace an manners to explain exactly what you want and why and then perhaps well meaning busy people like me will not waste our time - but don't criticise me for trying to help just because your original request was so general and didn't apparently cover hte points you eventually want to deal with.
FOR THE BENEFIT OF OTHERS RESPONDING - I believe Gen 2 engines do not have Lokasil bores.
No more responses from me to this topic - goodbye.
Baz
However may I make it clear that it is not the role of an initiator to a forum topic to dictate who may and who may not answer nor what content they may or may not feel is appropriate.
If you want specific responses than have the good grace an manners to explain exactly what you want and why and then perhaps well meaning busy people like me will not waste our time - but don't criticise me for trying to help just because your original request was so general and didn't apparently cover hte points you eventually want to deal with.
FOR THE BENEFIT OF OTHERS RESPONDING - I believe Gen 2 engines do not have Lokasil bores.
No more responses from me to this topic - goodbye.
Baz
Nelly strange response.
Surely in your situation the more you can learn about the cause of the problem the better position you and others will be when fighting your cause with Porsche. As for thinking that this just shouldnt happen on a Porsche well thats exactly the way it goes. They build their engines much closer to the limits than in the old days and the result is that a few of them fail early on in life.
When you ask for input and you get a good technical response from someone like Hartech you have just gained a whole load of info for free that others had to work very hard to get.
As for high cost failures on Porsches if you look back even at the older cars they all have their high value design flaws. Its nothing new, just that the later 911's seem to have this tendancy to need a whole new engine whereas in the past it was more the components that needed replacing rather than bottom end/ block failures.
Surely in your situation the more you can learn about the cause of the problem the better position you and others will be when fighting your cause with Porsche. As for thinking that this just shouldnt happen on a Porsche well thats exactly the way it goes. They build their engines much closer to the limits than in the old days and the result is that a few of them fail early on in life.
When you ask for input and you get a good technical response from someone like Hartech you have just gained a whole load of info for free that others had to work very hard to get.
As for high cost failures on Porsches if you look back even at the older cars they all have their high value design flaws. Its nothing new, just that the later 911's seem to have this tendancy to need a whole new engine whereas in the past it was more the components that needed replacing rather than bottom end/ block failures.
nelly997s said:
sorry
not happening to my bores
thanks for the input but i am interested in swapping stories and information with other owners regarding the lack of help we are getting
please open another thread if you want to talk about that subject
i accept you have a lot of info to add but this is about 80k cars that should not have problems at low mileages like this whatever the reason for it happening
The business that you get from this area of engine failures should not even be happening thats my point....!
no disrespect meant but we should not even need to be having this diversion if the topic if things were all fine
thanks for your comment
please add info if you can bring in some more owners who can share stories
How rude!not happening to my bores
thanks for the input but i am interested in swapping stories and information with other owners regarding the lack of help we are getting
please open another thread if you want to talk about that subject
i accept you have a lot of info to add but this is about 80k cars that should not have problems at low mileages like this whatever the reason for it happening
The business that you get from this area of engine failures should not even be happening thats my point....!
no disrespect meant but we should not even need to be having this diversion if the topic if things were all fine
thanks for your comment
please add info if you can bring in some more owners who can share stories
You're not going to get anyone 'on-side' with an attitude like that.
As has been said above, you just lost the best source of coherent, properly-researched and technically-sound information about the problems with the M96/7 engines you were ever going to find. Good start.
hartech said:
From this initial question "How many of you have problems or have had with your 997 cylinder liners? we need to form a register and join together to get some action or publicity" - I fail to see how a business that specifically repairs the problem and re-fits liners - and their experiences and technical issues are not valuable and frankly I am appalled at the dismissive response to my efforts to help. Obviously there is some hidden agenda that I am not privvy to yet and for some reason - me trying to help is putting a spanner in the plans - so to speak.
However may I make it clear that it is not the role of an initiator to a forum topic to dictate who may and who may not answer nor what content they may or may not feel is appropriate.
If you want specific responses than have the good grace an manners to explain exactly what you want and why and then perhaps well meaning busy people like me will not waste our time - but don't criticise me for trying to help just because your original request was so general and didn't apparently cover hte points you eventually want to deal with.
FOR THE BENEFIT OF OTHERS RESPONDING - I believe Gen 2 engines do not have Lokasil bores.
No more responses from me to this topic - goodbye.
Baz
A quite understandable response, talk about looking a gift horse in the mouth..............However may I make it clear that it is not the role of an initiator to a forum topic to dictate who may and who may not answer nor what content they may or may not feel is appropriate.
If you want specific responses than have the good grace an manners to explain exactly what you want and why and then perhaps well meaning busy people like me will not waste our time - but don't criticise me for trying to help just because your original request was so general and didn't apparently cover hte points you eventually want to deal with.
FOR THE BENEFIT OF OTHERS RESPONDING - I believe Gen 2 engines do not have Lokasil bores.
No more responses from me to this topic - goodbye.
Baz
The OP seems pretty clueless about what his issue actually is and doesn't seem to want to learn.
He also seems naive in the extreme to believe that gathering a few dozen or even hundred aggrieved owners together with no coherent or credible case is going to influence Porsche.
Good luck Nelly, you're going to need it.........................
I for one have found this thread very interesting, and the reason is because I did not know until reading this thread that there was a poblem with 997 bores.
I have even spoken to an OPC and had a very interesting conversation which confirms not only the Bore issue but also the RMS issue which still persists.
Why bother? Because up until Wednesday I was about to purchase eithe a GT3 or a 997 C2, and have put that purchase on hold until I can quantify the problem, is it occasional,insignificant, or inevitable.
Hartech's contribution was, to me at any rate, excellent. Baz identified the suspected issues and talked about the steps he is taking to isolate the problem rather than just treat the symptom, I expect Porsche already know but i doubt it will appear as an addendum to the 997 workshop manual.
But praise indeed to Nellie who started the thread and alerted me to potential problems.
I am still a potential owner (for the 2nd time) but as the car i will buy will be older I will have to take more care before deciding whether to purchase a Porsche or not.
Thanks to both of you for your contribution to this thread.
I have even spoken to an OPC and had a very interesting conversation which confirms not only the Bore issue but also the RMS issue which still persists.
Why bother? Because up until Wednesday I was about to purchase eithe a GT3 or a 997 C2, and have put that purchase on hold until I can quantify the problem, is it occasional,insignificant, or inevitable.
Hartech's contribution was, to me at any rate, excellent. Baz identified the suspected issues and talked about the steps he is taking to isolate the problem rather than just treat the symptom, I expect Porsche already know but i doubt it will appear as an addendum to the 997 workshop manual.
But praise indeed to Nellie who started the thread and alerted me to potential problems.
I am still a potential owner (for the 2nd time) but as the car i will buy will be older I will have to take more care before deciding whether to purchase a Porsche or not.
Thanks to both of you for your contribution to this thread.
Nelly to dismiss Baz in such a way is down rite rude. I understand your agenda but Porsche won't blink mate. Baz as far as harsh responses no way. You are a very well respected independant that it is trying to solve a fundemental engine issue of a major manufacturer, how bizarre is that. You are a dedicated man that deserves to reap the rewards.
Dont take it to heart Baz. Maybe this chap does not realise your contribution the to the world of Porsche owners up and down the country.
I was speaking to Paul and Matt the mechanics at Portiacraft on Sat and they reckon Hartech by investing heavily in the tools needed are saving a lot of early cars from only being fit for scrap when the engines go pop as they are possibly the only company offering a sensible solution to the problem and a well sorted 996 is still one of the best driving 911s and they now use them for all their engine work and I bet they are not the only one`s.
I was speaking to Paul and Matt the mechanics at Portiacraft on Sat and they reckon Hartech by investing heavily in the tools needed are saving a lot of early cars from only being fit for scrap when the engines go pop as they are possibly the only company offering a sensible solution to the problem and a well sorted 996 is still one of the best driving 911s and they now use them for all their engine work and I bet they are not the only one`s.
Thanks chaps - it's nice to be appreciated.
For the benefit of those appreciative readers - I thought I should add one important point that came to me afterwards.
Whenever we hear about the problem it is always described as cylinder scoring and no one else yet has taken one apart to reveal the problem is really that the piston seized and it was that damage that scored the bores.
It therefore occured to me that although many readers may think a seized piston is a different problem - it is actually the very same thing which I am just explaining the original cause of.
There are also some additionl reasons why the increase in torque and power at lower revs may push a marginal (but usally safe) coolant flow design - over the edge. One is that the water pump is running slower and that in turn is a recipe for local hot spots (basically localised boiling) that chases the coolant momentarily away from the cyliner wall and locally overheats the piston coating and or oil film strngth.
The 3.6 also has longer a stroke but the same coolant depth and the 3.8 has a bigger cylinder outside diameter but is inside of the block is the same original outside shape that all the engines had from 2.5 to 3.8 and hence the volume flowing inside is less and the ability for the coolant to dilute the temperature right at the cylinder wall surface with the coolant further away is reduced.
Anyway - when our tests are complete I will open a new subject revealing the results.
Meanwhile we do alter the flow characteriastics (we had to do something about it) but have not yet been able to quantify the results except that all those rebuilt since we modified the flow have been OK.
Baz
For the benefit of those appreciative readers - I thought I should add one important point that came to me afterwards.
Whenever we hear about the problem it is always described as cylinder scoring and no one else yet has taken one apart to reveal the problem is really that the piston seized and it was that damage that scored the bores.
It therefore occured to me that although many readers may think a seized piston is a different problem - it is actually the very same thing which I am just explaining the original cause of.
There are also some additionl reasons why the increase in torque and power at lower revs may push a marginal (but usally safe) coolant flow design - over the edge. One is that the water pump is running slower and that in turn is a recipe for local hot spots (basically localised boiling) that chases the coolant momentarily away from the cyliner wall and locally overheats the piston coating and or oil film strngth.
The 3.6 also has longer a stroke but the same coolant depth and the 3.8 has a bigger cylinder outside diameter but is inside of the block is the same original outside shape that all the engines had from 2.5 to 3.8 and hence the volume flowing inside is less and the ability for the coolant to dilute the temperature right at the cylinder wall surface with the coolant further away is reduced.
Anyway - when our tests are complete I will open a new subject revealing the results.
Meanwhile we do alter the flow characteriastics (we had to do something about it) but have not yet been able to quantify the results except that all those rebuilt since we modified the flow have been OK.
Baz
We're led to believe that modern manufacturing techniques mean that cars are robustly tested - as such how does such a basic and critical thing slip through the net?
Maybe Porsche have concluded the failure as a percentage of total engines/cars is within an acceptable limit - so whilst these issues do exist it will not be widespread?
Key question is therefore what is an acceptable limit - 5% failure????
Maybe Porsche have concluded the failure as a percentage of total engines/cars is within an acceptable limit - so whilst these issues do exist it will not be widespread?
Key question is therefore what is an acceptable limit - 5% failure????
Gassing Station | Porsche General | Top of Page | What's New | My Stuff