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securitycheck
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PostPosted: Thu Jan 08, 2015 3:19 pm    Post subject: Reply with quote

Baz, I understand bore scoring on 997's is rare (I've read <10%), and that its quite 'hit & miss', but in your experience, is a particular model year more prone than others?
 
  
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bo_duke
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PostPosted: Thu Jan 08, 2015 5:12 pm    Post subject: Reply with quote

I spent about a year looking for a rebuilt 997.1 C2S, with a manual gearbox. Annoyingly, the rebuilt cars always seemed to be tiptronic - Id estimate around 20 tiptronics to 5 manuals over the year. In the end, I gave up and bought a 996TT. Anyroad...

Having read that the tiptronic cars pull away in 2nd gear, I started to wonder if this might be a factor - more load at low revs, as they pull away in a higher gear?

Not looking to get flamed here by tiptronic owners, the ratio I noticed might just be my perception, or representative of new car sales! Just wondered what Baz might think of the theory.
 
  
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infrasilver
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PostPosted: Thu Jan 08, 2015 5:14 pm    Post subject: Reply with quote

That is one of Hartech theories anyway, the tip engine seems to suffer more for the reasons you mention.
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bo_duke
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PostPosted: Thu Jan 08, 2015 5:29 pm    Post subject: Reply with quote

Thanks infrasilver - didn't realise it was an established theory.
That being the case, it seems a shame the gearbox ECU cant be persuaded to default to 1st.
 
  
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infrasilver
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PostPosted: Thu Jan 08, 2015 5:32 pm    Post subject: Reply with quote

bo_duke wrote:
Thanks infrasilver - didn't realise it was an established theory.
That being the case, it seems a shame the gearbox ECU cant be persuaded to default to 1st.


It seems to back the therory up though if you were seeing that many more Tips with rebuilt engines.

I think (I'm not a tip driver) but you can put it into 1st before pulling away, Question
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T8
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PostPosted: Fri Jan 09, 2015 1:05 am    Post subject: Reply with quote

infrasilver wrote:


I think (I'm not a tip driver) but you can put it into 1st before pulling away, Question



Yep, you can and when the car is cold it defaults to first gear automatically.
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New997buyer
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PostPosted: Fri Jan 09, 2015 9:56 am    Post subject: Reply with quote

infrasilver wrote:
bo_duke wrote:
Thanks infrasilver - didn't realise it was an established theory.
That being the case, it seems a shame the gearbox ECU cant be persuaded to default to 1st.


It seems to back the therory up though if you were seeing that many more Tips with rebuilt engines.

I think (I'm not a tip driver) but you can put it into 1st before pulling away, Question


Could be but................

1) Correlation does not always mean causality. Switzerland consumes more chocolate per head of population AND produces more Nobel Prize winners, but that doesn't mean that chocolate makes you clever (and a secondary correlation that isn't a priori causal is that winning a Nobel Prize doesn't mean you're clever puh ). It could be a coincidence or causal. Until the mechanism is isolated it can't be taken as evidence it is a Tip only problem. But it could be a real breakthrough.

In short it is interesting but only in conjunction with other data.

2) Sampling bias may also be in effect. For whatever reason (not established) Tip's may be more prone to identification of the problems, OR Tips may be more likely to have the problems identified. Why? Who knows. But making sure some other reason for more Tips being prone isn't the reason over the failure itself needs to be understood, before any conclusion is drawn.

This isn't meant to say Tips aren't more prone, it is only saying that this without further evidence isn't a smoking gun.

'More research is required' is the standard phrase in these situations, but it could be a really valuable extra data point, building on the terrific empirical data already accumulated by Baz and his team at Hartech Thumb
 
  
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infrasilver
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PostPosted: Fri Jan 09, 2015 11:18 am    Post subject: Reply with quote

Hartech have always said they seem to weight the tip failures higher than the manual for the reasons mentioned about using the torque low down, and I believe this theory. The fact that someone has been specifically looking for a car with a rebuilt engine and found that 75% of those being sold (at the time he was looking) are tip at last points to a trend in the outside world. 75% is quite a high number to be a one off.
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bo_duke
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PostPosted: Fri Jan 09, 2015 12:47 pm    Post subject: Reply with quote

Could this be a useful survey, and/or would Baz be willing to share stats?

They have a couple of threads running on PH on 996/997 engine failures (links below) but neither state whether the affected cars are tiptronic or manual:

a) http://www.pistonheads.com/gassing/topic.asp?h=0&f=48&t=1052310&mid=416160&nmt=Has+your+996+or+997+engine+had+a+major+rebuild%3F

b) http://www.pistonheads.com/gassing/topic.asp?h=0&f=48&t=400915&mid=416160&nmt=996%2D997+wet%2Dsump+engine+reliability%3A+enter+your+stats+here%21

What they do provide though, is a list of people who have experienced engine failures, who could be invited to participate in a new survey.
 
  
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New997buyer
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PostPosted: Fri Jan 09, 2015 1:22 pm    Post subject: Reply with quote

infrasilver wrote:
Hartech have always said they seem to weight the tip failures higher than the manual for the reasons mentioned about using the torque low down, and I believe this theory.


In science and engineering there is no belief: only empirically demonstrated claims (i.e. a theory) or non empirically demonstrated 'hunches' (a hypothesis). The Tip link to bore Scoring at this stage looks like the latter to me, at this stage. But to become a theory until, as you rightly point out, more evidence is needs to be put forward from other data points outside Hartech Grin

I wouldn't set foot near a plane that the engineer told me he believed is safe Thumb
 
  
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infrasilver
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PostPosted: Fri Jan 09, 2015 2:12 pm    Post subject: Reply with quote

There are not many facts regarding (most) failures of these engines, you can only go on what evidence is out there, then look at how the engine was designed and make educated decisions.
There is no hard evidence anywhere to suggest one is worse than the other but I have read plenty on the subject to deduce where the evidence is pointing. The stroke that puts most pressure on the thrust face when the engine oil is at its thinnest and torque is at it highest makes a good claim for the high percentages and I still believe this.
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New997buyer
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PostPosted: Fri Jan 09, 2015 2:29 pm    Post subject: Reply with quote

infrasilver wrote:
There are not many facts regarding (most) failures of these engines, you can only go on what evidence is out there, then look at how the engine was designed and make educated decisions.
There is no hard evidence anywhere to suggest one is worse than the other but I have read plenty on the subject to deduce where the evidence is pointing. The stroke that puts most pressure on the thrust face when the engine oil is at its thinnest and torque is at it highest makes a good claim for the high percentages and I still believe this.


Question I think you think I'm arguing with you when I'm having an honest but questioning discussion....... Dont know
 
  
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infrasilver
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PostPosted: Fri Jan 09, 2015 2:35 pm    Post subject: Reply with quote

New996buyer wrote:
infrasilver wrote:
There are not many facts regarding (most) failures of these engines, you can only go on what evidence is out there, then look at how the engine was designed and make educated decisions.
There is no hard evidence anywhere to suggest one is worse than the other but I have read plenty on the subject to deduce where the evidence is pointing. The stroke that puts most pressure on the thrust face when the engine oil is at its thinnest and torque is at it highest makes a good claim for the high percentages and I still believe this.


Question I think you think I'm arguing with you when I'm having an honest but questioning discussion....... Dont know


I don't think there is an argument, I just wonder why you are questioning my choice of words, I know what believe means?
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New997buyer
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PostPosted: Fri Jan 09, 2015 2:47 pm    Post subject: Reply with quote

infrasilver wrote:


I don't think there is an argument, I just wonder why you are questioning my choice of words, I know what believe means?


I'm not questioning, I'm clarifying... Dont know
 
  
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wizard993
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PostPosted: Fri Jan 09, 2015 4:09 pm    Post subject: Reply with quote

infrasilver wrote:
There are not many facts regarding (most) failures of these engines, you can only go on what evidence is out there, then look at how the engine was designed and make educated decisions.
There is no hard evidence anywhere to suggest one is worse than the other but I have read plenty on the subject to deduce where the evidence is pointing. The stroke that puts most pressure on the thrust face when the engine oil is at its thinnest and torque is at it highest makes a good claim for the high percentages and I still believe this.



Agreed.
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Kev M
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PostPosted: Tue Feb 14, 2017 12:04 am    Post subject: Reply with quote

Does the Gen 2 have the bore scoring problems?
 
  
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spongebob squarepants
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PostPosted: Tue Feb 14, 2017 5:50 am    Post subject: Reply with quote

Kev M wrote:
Does the Gen 2 have the bore scoring problems?


All engines can suffer bore scoring, it's the reason why its happened that's the important thing. The Gen 2 is a safe bet, if you got bore scoring which would be virtually unheard of on a gen 2, it wouldn't be down to faults in the engine design (like the gen 1)
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bazhart
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PostPosted: Tue Feb 14, 2017 10:07 am    Post subject: Reply with quote

It's all very well new997buyer stating that there is a need for more data - of course there always is - but this attitude is a dead end rather clever negative glass half empty comment.

It also fits neatly into the proof of if we are really all here or are just experiencing a dream!

Nothing can be absolutely proven and all conclusions, laws and technology is open to amendment as new information becomes available.

Perhaps you could state what else we should do in order to decide on investing time and money on a particular affordable and better solution so owners have an alternative option to a new engine with the same design?

Hundreds of owners have benefitted from our provisions that have come about as a result of our tests, forensic analysis, engineering expertise and data acquisition - without which we would never have invested in them.

What all very good engineers know and will agree with is that over the years it is possible to form reliable conclusions from reasonably scant feedback as long as the data combines with the engineering analysis, forensic analysis and testing results.

In this case the failures are linked to thrust loads not piston expansion (or the scoring would be on both sides of the pistons).

Tests we conducted with temperature sensors fitted in the engines demonstrated times when the temperature in the area of the scoring increased and this results in thinner oil films and closer contact of the piston face with the cylinder wall.

Tests with pistons with different piston coating showed that the type of coating and its hardness at elevated temperatures made a soften coating likely to score first.

Accepted research (available on the Internet) lists bore scuffing (which is the correct term for bore scoring) as occurring at lower engine speeds and higher torque.

Dynamic analysis shows that as the piston speed increases the tendency to skip over the bore surface increases - so is more likely to score at lower revs.

Tribology and fluid dynamics prove that a thin film of oil between two surface under pressure will leak out quicker if the viscosity is higher.

It is undeniable that at twice the revs there is half the delta time for that oil to squeeze out and result in a thinner lubricating film between the piston and the bore.

Tiptronics pulling away in second apply more torque. Research we conducted proved to us that when driving a manual - most drivers do not change gear until a higher rev has been reached compared to the same person driving the same model in tiptronic form.

A low temperature thermostat helps increase the thickness of that oil film through running the car at a lower oil temperature.

What is true is that you have to be very good indeed at combining basic technical engineering knowledge of a wide range of subjects with a practical understanding of engines and their faults, experience of fixing them and have the where with all, facilities, intention, resources and drive to put into motion extensive tests and data feedback to be sure of your conclusions and there are very few independents that can put all that together.

But as I often remark - there seems to be 2 specific types of people = one type = glass half empty - always criticising what others do and achieve but as a result actually achieve little similar themselves and glass half full, optimistic, risk takers that are interested problem solvers that come up with alternatives that work.

Glass half full people will never convert the glass half empty ones so as long as readers understand this - I am confident that they can form their own conclusions about what to take notice of.

Apart from that I sometimes wonder about the position people put themselves in when they question a business that has for well over a decade repaired hundreds of failed engines with a brilliant reputation using the technology their research suggested formed the right conclusions.

I hope our new 997 owners do not experience bore scoring but if they do then I am sure they could benefit from the many specialists that were prepared to put their money where their mouth is and invest in providing less expensive and in my opinion better quality repairs than a simple like for like replacement.

With the very small statistical evidence they have to work with they do in my opinion deserve at the very least some support rather than clever theoretical responses from those in a less relative position to judge.

Kev M - no it seems that Gen 2 (9A1) engines will not suffer bore scoring but some have suffered piston seizures that have then let free as the damage reduces the piston diameter.

My research suggests that this will only occur after a long period of time (several years in most cases although it could be sooner I'm extreme cases).

I cannot determine how many will suffer - it may be very few or it may be quite a lot. Only time will tell that answer because it depends on a number of time based factors and some related to manufacturing tolerances (that always vary within a range).

As you may we aware from other posts and topics - I have been trying to increase the amount of data available on this potential problem by inviting responses from anyone who has experienced it. After very little feedback the results are identical for all. The forensic analysis demonstrates a trend that would explain it technically - although you would need wide engineering experience and study/qualifications to understand the processes and contributory factors.

As a result I am prepared to invest in a solution currently in prototype production - which many will no doubt appreciate rather than try and discredit with generalisations about limited data acquisition.

Baz
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RXBoxster
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PostPosted: Tue Feb 14, 2017 10:13 am    Post subject: Reply with quote

Ive figured out a way to totally stop bore scoring Smile Cool
 
  
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Kev M
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PostPosted: Tue Feb 14, 2017 1:27 pm    Post subject: Reply with quote

Thanks for the detailed response Baz Thumb

I looked a Cayman S two year ago which was 3.4 if i recall which had been rebuilt with just 34k on the clock due to bore damage. The engine built used Omega forged pistons which i was reliably told was the best option to negate this problem with coatings. I decided not to buy due to the engine history.

The whole dream / idea of buying a Porsche is its a lifetime achievement it would be so disappointing to have the dream ruined by a costly known issue. Having looked at other vehicles they all have their problems so every choice has a risk.

Given the Gen 2 does not seem to have the problem then my search will continue thumbsup
 
  
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