996-997 wet-sump engine reliability: enter your stats here!

996-997 wet-sump engine reliability: enter your stats here!

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Discussion

Gary11

4,162 posts

200 months

Tuesday 15th November 2011
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[quote=hartech]"Gary, I don't like doing that"

Thats fine Baz I appreciate your taking time to reply!
I like you have rebuilt many engines and used to enjoy working on my own cars and motor bikes back when god was a boy,those days are long gone,however the field you work in is specialised complex and evolving. I am in a mechanical Porsche orientated envioroment on a daily basis,I cannot think of many even specialist workshops capable of these rebuilds and improvements. I think you do an excellent job. You will always get know all type people putting pen to paper trying to prove a point.
I wouldnt advocate putting any overheated and consequently overstressed and weakened component back in a performance engine,just the suggestion of that confirms the level of the authors expertise you dont put back "what you can get away with" with these type engines.. unless you want another costly failure.I wouldnt worry, we all learn new things from new people and new problems.I find threads like this very constructive,helping a lot with early symptoms diagnosis.
G

Edited by Gary11 on Tuesday 15th November 11:39


Edited by Gary11 on Tuesday 15th November 12:07

mollytherocker

14,365 posts

208 months

Tuesday 15th November 2011
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Gary11]artech said:
"Gary, I don't like doing that"

Thats fine Baz I appreciate your taking time to reply!
I like you have rebuilt many engines and used to enjoy working on my own cars and motor bikes back when god was a boy,those days are long gone,however the field you work in is specialised complex and evolving I am in a mechanical Porsche orientated envioroment on a daily basis,I cannot think of many even specialist workshops capable of these rebuilds and improvements> I think you do an excellent job you will always get know all type people putting pen to paper,I wouldnt advocate putting any overheated and consequently overstressed and weakened component back in a performance engine,just the suggestion of that confirms the level of the authors expertise you dont put back "what you can get away with" with these type engines unless you want another costly failure,I wouldnt worry, we all learn new things from new people and new problems.I find threads like this very constructive,helping a lot with early symptoms diagnosis.
G

Edited by Gary11 on Tuesday 15th November 11:39
Phew! A full stop wouldn't kill yer!biggrin

MTR

Gary11

4,162 posts

200 months

Tuesday 15th November 2011
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mollytherocker said:
Phew! A full stop wouldn't kill yer!biggrin

MTR
Sorry I edited it out before repunctuating it LOL.

screwloose

608 posts

204 months

Sunday 11th December 2011
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Apologies but I've jumped in this topic fairly late on.
Am I right in thinking turbo and gt derivatives of both 996 and 997 are relatively immune to the issues highlighted in this topic?
Ta

mollytherocker

14,365 posts

208 months

Sunday 11th December 2011
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Yes, they are a different engine.

MTR

Globs

13,841 posts

230 months

Sunday 11th December 2011
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mollytherocker said:
Yes, they are a different engine.

MTR
Yup - the only thing I would perhaps change as routine in a Turbo/GT engine would be the camchain and water pump.

mollytherocker

14,365 posts

208 months

Saturday 17th December 2011
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Reading another thread about how many people have OPC warranties due to the fear of these issues, I find myself wondering if, ironically, Porsche have actually profited from these failures?

The revenue from the warranty, inspections, servicing, necessity for genuine parts etc must significantly exceed the cost of replacement engines?

Just a thought.

MTR

hartech

1,929 posts

216 months

Saturday 17th December 2011
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Well done MTR you have begun to see some of the issues we are not comfortable to expose or suggest - but also consider - just like you have.

I think that it is the way the World is moving - to compensate for the huge increases in labour rates for anything needing skilled labour while mass production has reduced relative unit costs - making replacement more viable in many cases than repair. All you do is pay so much regularly into a kitty and those that need to take advantage of the cover provided are paid for by those that didn't.

It is like a classic insurance situation (as we have always suggested) - likelihood of a claim remote - but the cost if it happened - too high to just ignore - so instead pay a smaller out regularly to protect your investment - just like you do for your house - your car - and more and more do for their plumbing, central heating, etc, etc. it is a sensible response to global changes in World economics and makes good sense most often.

However it is still a free market enabling other alternatives to be considered - as those on our version (the Lifetime Maintenance plan) have done.

What is becoming less and less viable overall - is to simply take no protection and take your chances - as more and more are regretting doing.

Baz


hartech

1,929 posts

216 months

Friday 23rd December 2011
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The new section 5 of our Internet based buyers guide about cylinder scoring has now been uploaded (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,

Cicerosecundus

14 posts

173 months

Tuesday 27th December 2011
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2001 996 107,000 miles. Uses very little oil. Minor repairs. Replaced rear main seal and the intermediate shaft bearing assembly with the Inengineering aftermarket bearing assembly when the clutch was replaced. Neither had failed - preventive maintenance. Change Mobile 1 at 7K miles. Put in 180 degree thermostat and my 996 seems to run a bit cooler. Am very careful to warm up engine at below 3K RPM and use my 996 as a highway commutation car. My 996 rarely gets above 5K RPM and is very very rarely above 6RPM. I work the gears to keep the RPMs at all times at or above 3K. Put in the 997 shift assembly and cables and the transmission shifts better than the stock 996 shift assembly - indeed, it shifts so much better and with a shorter throw that it was worth the cost, although there was nothing defective or worn in the factory's 996 shift assembly. My after market Porsche technician warned me that despite my care, I will need a full rebuild at around 150K, barring bad luck before that. Drove two Mercedes diesel sedans to 250,000 miles before selling them. Don't expect that performance from a high performance gas engine, but would feel cheated if I could not get 150K miles out of a Porsche. I hope that VW management surfs the Internet for Sites like Piston Heads and forces Porsche to improve the durability of its engines.

hartech

1,929 posts

216 months

Wednesday 28th December 2011
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You seem to have all you can so far Sicerosecundus - and should have the best chance of anyone to keep it running. The only thing possibly to go wrong (which you can do nothing practical about with a rebuild) is that a cylinder cracks or "D" chunks - or possibly a shell wears out.

So far the nearest we got was 153K and then a crack - several from 40 to 50K and a lot around 70 to 80K - but they will not be taking the care you are over oil changes or warming up etc - good luck and I hope it gets there - if it does I recommend you get someone over there to rebuild it and re-sleeve it or re-round the cylinders and cvhange to a closed deck design.

I also guess the roads and speed limits in the USA may lend themselves to helping such an engine through reducing both hihg speed use and start/stop acceleration runs which lead to the sort of temperature fluctuations that speed up the "creep" that distorts the bores.

Hoping to hear that you got there one day.

Baz
Baz

Cicerosecundus

14 posts

173 months

Tuesday 3rd January 2012
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Thank you Baz for your thoughtful response.
Yes, I know that the odds are against my getting to 150K without one of the engine disasters that the 996 is prone to. However, at my C4's age and mileage, my like new looking and performing C4 has but minor residual value, so I am thinking that I will just drive it until the engine breaks and then decide whether to rebuild it at a cost greater than its resale value or just donate it. I will have had by then 12 to 14 years of constant and extremely pleasurable use. My last S body Mercedes diesel reached 230,000 miles and looked and drove as new. I did not find a buyer due to the mileage, so I ended up donating it to a religious organization for a tax deduction.
By the way, you refer to a "closed deck." Would you be so kind as to educate me as to what a closed deck is and why it is superior? If you have already done that in one of your messages to this Forum, just point me to your message. Many thanks for your many highly educational responses in this Forum.
And yes, my driving conditions in the NYC area in which I commute an hour each way during rush hours to an office in mid-Connecticut from just outside NYC do not allow the kind of play that we Porsche owners dearly love. But, I can cruise on the Merritt Parkway, a beautifully landscaped winding highway, at a steady 80MPH and can overtake at much higher speed when I see an opening. But, it is very disciplined driving and there is no opportunity to do anything serious that would stress the 996 engine. I should point out that I am very careful to keep the RPMs between 3 and 5K and this is my fifth sports car since I was a student. I have noted that many but not all of the Porsche owners in the US that protest on the Internet that they have lost their 996 and 997 engines at low mileage bought a Porsche as their first sports car. I learned beginning at a young age on an Austin Healey Sprite, a TR3 and a TR4, a Morgan and a 912. With the British sports cars I learned the hard way to listen to the slightest change in the sound or performance of an engine and to react proactively at the slightest symptom. Cicerosecundus

hartech

1,929 posts

216 months

Tuesday 3rd January 2012
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Happy new year to everyone - Cicerosecundus - a quick answer may generate more qusetions - so this is more lengthy - sorry. The "closed deck" refers to the design of the top of the cylinder block. To avoid more questions from others I have provided this comprehensive explanation.

The round hole that the pistons run up and down inside (the cylinder bore) used to be cast as part of the whole engine and the cylindrical bit was joined to the outside of the cylinder block in various places with small holes and cavitites to allow coolant to flow from the cylinder block up to the cylinder head. This enabled the outside of the block to partly support the round cylinders inside and keep them from moving about and this is a "closed deck design" likened to the deck on a ship being near the top and closing off the cabins underneath (or decking set over a framework) and similarly the top part of the block being closed off (like a ships deck) or open.

Porsche have always been at the front of trying to build engines with good low and mid range torque and to do this the pistons need to be a tight fit inside the cylinder bore so the pumping efficiency when the cams are not running at their ideal revs - is still good.

Sometimes the bits of the casting connecting the cylinder to the outside (usually where the cylinder head studds pass through) could slightly distort the cylinder from being perfectly round during thermal expansion etc and to allow for this the piston to bore clearance had to be a little larger than would be ideal if it wasn't for the distortion.

The engines with iron/steel liners cast in did not distort so much as the iron/steel was strong enough to partly resist this distortion, but when all aluminium cylinder blocks with hard surface treatments were contemplated (for lighter engines and less bore wear) this distortion became more of an issue.

The 944 and 968 Porsche engines had the cylinder bore cast like a tube sticking up into the block with nothing connecting it to the outside of the block - making it like a free standing tube just joined near the base or near the lower end so the "hot top" area was free to avoid any thermal stresses from distorting it and so ran tighter bore clearances successfully and this was called an "open deck design".

However the aluminium used for this engine has silicon particles cast into it (to provide the hard part of the cylinder bore) which made it stiffer than ordinary alloy cylinder blocks - so when the piston pushes on the cylinder bore to drive the car along - very little distortion resulted and the design made a very stable and strong cylinder bore. Only very highly tuned special racing turbo versions ever cracked a bore and then only after very high mileages. This system was called Alusil and was very successful for a liquid cooled engine.

The air cooled 911 versions also had alloy cylinders but this time with Nikasil plating on the bores. They remained very round because the fins (like a traditional motorcycle engine) formed circular rings around the bore to help keep it round and enabling tight piston clearances again to great benefit.

When the M96/M97 (996, 997 and Boxster) engines were built they copied the cylinder layout of the previously successful 944/968 range but this time the cylinders were cast in alloy inside which "Lokasil" tubes were cast (rather like a cast in iron liner) but unlike cast iron the composite nature of the liner meant is was not as strong as cast iron or the Alusil blocks - and in addition the type of composite is known to suffer a relatively new phenomenon (compared to metals) of "creep" in which after repeated stress cycles and the application of heat - the material slowly distorts in the direction of the load. In these engines they distort "oval" rather like if you squeezed the sides of an open tin can so it got wider in one direction and narrower in the other.

Porsche seemed to anticipate this by modifying the cylinder head gaskets to allow for some movement but eventually of course it results in large bore clearances and a fatigue crack or a piece falling out all together. I don't know if they understood that this would eventually limit the engine lifespan or not. Some aspects of the design suggest not as things like the metal inserts in the crankshaft housing are there for long life expectations but in contradiction - other aspects like crankshaft shell width and quality suggest otherwise and of course there are no oversized pistons or undersized shells listed - so replacement engines became the norm rather than rebuilding them (until businesses like ours and others found ways to rebuild them anyway).

In the Generation 2 engines I believe Porsche have reverted to the Alusil system and in addition to that design from the 944/968 have closed off the top deck as well - which should result in a very good system indeed which they have published glowing reports about.

What we offer as an option when we rebuild the "open deck" engines is to squeeze the "oval bores" round again and fit in a ring that connects the outside of the cylinder to the inside of the block and converts the design from an open deck to a closed deck system to keep the cylinders round while preventing them from distorting oval again. More details and pictures on our buyers guide sections 4 and 5 on www.hartech.org

I hope this helps - it is a complicated subject.


Baz









Globs

13,841 posts

230 months

Tuesday 3rd January 2012
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Hi all, happy new year!

A picture is worth a thousand words wink

Closed deck:


Open deck:


As Baz says you can see how well supported the cylinders are in a closed deck at the top.

hartech

1,929 posts

216 months

Tuesday 3rd January 2012
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Thanks Globs that's a great idea. I am not as good as you with photos - but will try

picture of a 996 block with a pice missing and one after we have fixed the top with support rings.



I have got better ohotos in the files somewhere but not time to find them - but these show the basics that combined with your support the explanations above (I hope).

Baz

Richie200

2,011 posts

208 months

Wednesday 4th January 2012
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Baz this is incredible effort and real dedication to improve the standard of knowledge amongst the Porsche owners here, thanks for all your support. One small, hopefully easy question for you: I have a C2.1 3.4l with a full Hartech rebuild 7000miles ago (previously owned by Henry Ward) and am contemplating buying one of these:

http://www.design911.co.uk/fu/pt697_1663_-cma81-cm...


One thing that I am now slightly concerned with now, having read your previous few posts here is that, as the water cooled engine has been pushed so close/over the limits, would fitting the above item once again jeopardise the reliability of my engine (still under warranty). Also do you have any experience with these IPD plenums, they claim a 25bhp gain, is this the case or would you recommend not going down this route?


Edited by Richie200 on Wednesday 4th January 14:50

Gary11

4,162 posts

200 months

Wednesday 4th January 2012
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Richie200 said:
Baz this is incredible effort and real dedication to improve the standard of knowledge amongst the Porsche owners here, thanks for all your support. One small, hopefully easy question for you: I have a C2.1 3.4l with a full Hartech rebuild 7000miles ago (previously owned by Henry Ward) and am contemplating buying one of these:

http://www.design911.co.uk/fu/pt697_1663_-cma81-cm...


One thing that I am now slightly concerned with now, having read your previous few posts here is that, as the water cooled engine has been pushed so close/over the limits, would fitting the above item once again jeopardise the reliability of my engine (still under warranty). Also do you have any experience with these IPD plenums, they claim a 25bhp gain, is this the case or would you recommend not going down this route?


Edited by Richie200 on Wednesday 4th January 14:50
I would be supprised if this would give a 25bhp gain in my experiance its more like 8bhp if your lucky.

hartech

1,929 posts

216 months

Thursday 5th January 2012
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It depends a lot of where in the rev band the claimed improvement occurs. To make a comment I would need to see a before and after torque or bhp graph - but I am guessing it will mainly be at the top end - and if so find it hard to believe - but best to see the power graphs first and then think about a response afterwards.

Baz

Richie200

2,011 posts

208 months

Thursday 5th January 2012
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If you scroll down to the 4th model on this site "996 Carrera 2 3.4L (1998-1999) Cable Throttle" you will see 2x Dyno graphs:
http://www.ipdplenums.com/index.php?option=com_con...

The IPD "Y" designed Cable plenum is a direct factory replacement of the OE "T" style air distributor. The IPD Plenum provides impressive max horsepower gains of 28 in the mid range and an additional 12 horsepower on top



Edited by Richie200 on Thursday 5th January 11:42


Edited by Richie200 on Thursday 5th January 11:46


Edited by Richie200 on Thursday 5th January 11:47

hartech

1,929 posts

216 months

Thursday 5th January 2012
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Thanks Ritchie, on the basis of those graphs I would expect it to be OK prociding the engine etc was in general good condition and a good quality oil was in use, radiators all clean etc.

Baz