C.B.B.C.- Cayman big bang club.

C.B.B.C.- Cayman big bang club.

Author
Discussion

ilduce

Original Poster:

485 posts

126 months

Saturday 19th April 2014
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The initial message was deleted from this topic on 09 May 2015 at 11:06

Ozzie Osmond

21,189 posts

245 months

Saturday 19th April 2014
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It's a good question. My dealer says they've never had to dismantle a 3.4 litre engine.

g7jhp

6,959 posts

237 months

Saturday 19th April 2014
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Ozzie Osmond said:
It's a good question. My dealer says they've never had to dismantle a 3.4 litre engine.
They probably just replace it with a new engine!

paranha

633 posts

241 months

Monday 21st April 2014
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Does this assume it is only the 3.4 Engine?.How many 2.7s have Hartech or OPC.s revived?.

paranha

633 posts

241 months

Monday 21st April 2014
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Thankyou--Long may that Continue ----

tr7v8

7,186 posts

227 months

Saturday 26th April 2014
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AFAIK D hunk was only early 2.5 Boxsters, the M96/97 engine suffers other issues such as IMS, Bore Scoring & Oval bores. A more minor issue is RMS leaks.

tr7v8

7,186 posts

227 months

Saturday 26th April 2014
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Ouch, news to me I wasn't aware later cars did it eek

paranha

633 posts

241 months

Saturday 26th April 2014
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So sorry to see the photo------------What mileage?.

hartech

1,929 posts

216 months

Saturday 26th April 2014
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In the short term it is cheaper to manufacture a casting with the top of the cylinder just a round circle compared to a closed deck design - as this prevents the need for hardened sand cores to be placed in the mould and enables higher pressure castings to be used which usually result in more accuracy, better material consistency and lower production costs.

However it leaves the cylinder free to flex under the pressure from the piston pushing on one side of the cylinder bore to drive the car along and like a baked bean tin - if you squeeze it in one direction - it goes oval.

It does this every time a power stroke is applied - so perhaps on average 1500 times/minute of normal driving.

The manufacturers know flexing occurs and to prevent this resulting in chatter at the cylinder head gasket often relive the gasket design to allow it to flex yet stay located to the mating faces (as in this case).

The problem is made worse if the cylinder thickness is too thin as this directly reduces the strength of the cylinder tube and increases the amount of flexing until metal fatigue results in a crack.

The original 944 and 968 version of an open deck cylinder had much thicker wall thickness cylinder tubes and a stronger material - and lasted OK (except in extreme turbo applications).

These are made of less strong (but easier to machine) alloy with a weaker central core material and to prevent this "D" chunking they needed to be thicker, stronger or fitted with a top security ring. The larger the piston (and the faster the car is driven) the greater the forces and the sooner they fail - so it is hardly ever seen in anything under 3 litre, rarely (or only on very high mileage examples) in a 3.2, but increasingly evident in a 3.4, 3.6 or 3.8 versions.

When we repair a "D" chunk by fitting a new alloy cylinder we also convert the new cylinder to a closed deck design so it cannot distort oval again and therefore will not crack again. At the same time we offer customers two further improvements to the remaining cylinders. The first is to re-round the otherwise permanently oval cylinders (now with too much piston clearance) and fit an auxiliary security restraining ring to convert them to a closed deck design as well and the second is to replace all cylinders with new alloy cylinders.

In the past few years there has been several alternatives offering steel (or iron) liners - with or without Nikasil coatings that is minimally cheaper than our alloy Nikasil liners. Almost every week we hear from yet another specialist who has tried this and found that they failed - with too much oil consumption or liner slip. The difference in piston expansion rates and piston clearances needed to allow the right clearances from driving such a car at 30mph and 170 mph are beyond the ability of these different materials with widely different expansion rates to cope. If the cold and slow driving clearances were right for good oil consumption they would be too tight when the engine was flat out and similarly if they were right when it was flat out they would be too large to resist high oil consumption at low speeds. This is why manufacturers of high performance sports cars with large pistons exclusively try different types of all Alloy engines and cylinders - and have done for many years.

If the cylinder bore diameter is smaller, steel/iron liners can be made to work as the relative expansion in total is reduced and if they are cast in (as many are) this prevents the slip caused by differential expansion).

We know how to (and therefore could) fit similar liners so they didn't slip but know that it is not the right long term solution and resisted offering it as an alternative - despite initially losing some business as a result of other offering it.

Since then our decision has been totally vindicated and while our liners continue to prove a complete solution, more and more specialists are coming back to us, having had their fingers burned trying to save a very small amount for a solution that has been discredited for this type of engine for several decades - meanwhile our pile of replaced steel liners (originally fitted elsewhere) continues to increase (as witnessed by 2 different Porsche Club visiting members in the last few months). In the last week we have heard again from a respected specialist who for some reason decided to try this steel/iron solution and has already rebuilt the engine twice and still without it working properly.

It is no surprise that the more powerful (and regarded as almost bullet proof) GT and Turbo versions of the same models also fit alloy Nikasil closed deck cylinders of very similar design to ours and that these prove extremely reliable.

It would have cost very little during manufacture to fit restraining rings to every engine and this in itself would have prevented early "D" chunking.

Unfortunately several years of production of a wide range of versions - are of this design and - will gradually have increasingly oval cylinders, increasing piston clearances and probably "D" chunk one day although the pressure from the piston (losely related to the amount of throttle opening and aggressive driving) also increases the ovality rate and those driving more carefully may well get high mileages out of the cars without cracks - but then - why did they buy such a fast car if they didn't intend to use the performance - you might ask?

The first time we saw inside one of these engines (over a decade ago) we predicted cylinder ovality and "D" chunking would result so researched and designed a solution that would eradicate that possibility - so it is surprising that the small extra cost of fitting restraining rings was not adopted during manufacture as in the long run it would have improved the reputation of the manufacturer and saved in warranty replacement costs.

Meanwhile we are often accused of scare mongering about the long term expectations and similarly to be unnecessarily running down the steel/iron solution - often with the argument that some F1 engines use steel liners. This simply is an uneducated conclusion not realising that it is easy to build an engine with the right clearances for either modest power or continuous flat out performance but that the problem for road cars with relatively large piston diameters - is finding a solution that works perfectly for both thermal extremes.

The Gen 2 engines have reverted to a closed deck cylinder design and so should prevent this type of failure although there are already some signs that other cost saving measures will emerge with a few failures for other reasons.

Regardless of all this - the vast majority of owners actually never use even a fraction of the available performance (or only rarely) and as a result they still get acceptable mileages out of the cars without failures and so this is still a relatively rare problem affecting relatively few examples - so there is no need to panic over the weaknesses these engines incorporate (especially for those intending to use the car's full performance potential).

Meanwhile they are fantastic cars to own and drive and there are several different types of cover you can obtain to remove or minimise the repair costs if the worst happens. Furthermore the oldest examples are reaching an age (and lower cost) when it is not unreasonable to consider a preventative rebuild that incorporates various improvements for longevity.

Baz




LaurasOtherHalf

21,429 posts

195 months

Saturday 26th April 2014
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hartech said:
The Gen 2 engines have reverted to a closed deck cylinder design and so should prevent this type of failure although there are already some signs that other cost saving measures will emerge with a few failures for other reasons.....


Baz
Interesting, care to expand?

Trev450

6,314 posts

171 months

Saturday 26th April 2014
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A quick question, Baz.

When replacing pistons and liners in the 3.4, can you incorporate an increase to cubic capacity option such as the 3.7 litre one that Autofarm offer.

Zyp

14,673 posts

188 months

Saturday 26th April 2014
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ilduce said:
tr7v8 said:
AFAIK D hunk was only early 2.5 Boxsters, the M96/97 engine suffers other issues such as IMS, Bore Scoring & Oval bores. A more minor issue is RMS leaks.
YKL.
Here is my 2007 Cayman 3.4 with a D-chunk.
Is that a dfi engine?

rob.kellock

2,213 posts

191 months

Saturday 26th April 2014
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They weren't selling them in 2007, unless that's a DeLorean...

Zyp

14,673 posts

188 months

Saturday 26th April 2014
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Of course, it would help immensely if I read things properly before replying...

ChrisW.

6,210 posts

254 months

Saturday 26th April 2014
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A very useful reply Baz smile

graemel

7,017 posts

216 months

Saturday 26th April 2014
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As always Baz very informative.
It gawls me that for the sake of what a few hundred pounds, Porsche could have built closed deck engines and aleviated these problems. That said and I mean it in a good way. Their F up has allowed you to build and establish a very good business. So out of something bad, something good has come.

mollytherocker

14,365 posts

208 months

Saturday 26th April 2014
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Zyp said:
Is that a dfi engine?
No, the DFI is a closed deck design.

Ozzie Osmond

21,189 posts

245 months

Sunday 27th April 2014
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If you summarise all that detail what is it that causes the problem to emerge,

  • Regular high rpm?
  • Regular high torque?
  • Using too much power from a cold engine"
  • Slow engine warm-up?
  • rpm too low with a cold engine?
  • Too much gentle driving?

NicD

3,281 posts

256 months

Sunday 27th April 2014
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graemel said:
As always Baz very informative.
It gawls me that for the sake of what a few hundred pounds, Porsche could have built closed deck engines and aleviated these problems. That said and I mean it in a good way. Their F up has allowed you to build and establish a very good business. So out of something bad, something good has come.
Yes, would be nice to see the discussions and internal engineering white papers before the design was signed off.

JMGPorsche

36 posts

155 months

Sunday 27th April 2014
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From a specialists perspective, one thing that I think Barry at Hartech will agree with, which may not be clear from forum posts and could potentially cause people to avoid a Boxster, Cayman, 996, 997 or even a 991, is that these failures are much less common than internet posts might suggest.

D-Chunk, Oval-Bores, RMS leaks, IMS Failure etc all have happened, and when they do happen, they happen in exactly the same way, but other than that, these engines do not seem to suffer things which usual engines might suffer, such as engine wear... I have customers with 300,000 miles on an original engine without issue.. But I have also seen the occasional poor bugger suffer any of the above common failures, and when they happen, it sometimes happens to the most pampered cars.

As an example of how rare these things are.. Every day we see several Boxster, Cayman, 996, 997 and the odd 991.. Thats a lot of example cars.

If the failure is an IMS Bearing failure, RMS, chain, oil scavenge pump, cam followers, head gasket, etc.. We deal with it in house.. Anything to do with the Block, such as D-Chunk or oval bore, we post the engine to Hartech and are completely transparent about that, but only charge what Hartech would charge direct.. Which, in itself, is an indication of how rare these problems are.. If we had more than one car a year suffering D-Chunk or oval bores, we would deal with them in house.. But what Hartech offer is a centralised expert service on reclaiming the crankcases after failure and making them better than new... But it really is that rare.

We have seen only a very few cars d-chunk.. from memory a 2.5 Boxster in 2002, a 3.4 996 in 2004, another 3.4 996 in 2007 and that is it.

Of IMS bearing failures, I think we have seen one 3.4 996 in 2007, but have seen roughly 3 to 5 IMS Bearing failures per year on 3.6 996 models per year, but no 997's, 987-Boxsters or Caymans.

Bore ovality, or as it prefer to call it drooping bores, I have seen maybe one a year, and it is always a 997 or 987 based engine. Maybe it is early days.

It really is the minority..

With the 996 and 986 Boxster, it is well worth having your IMS bearing updated at the same time as a clutch, just as insurance..

If you have a coolant change, waterpump, expansion tank etc.. Get the cooler thermostat at the same time..

And although I have not seen any direct evidence of a link between oil system issues (everything from cam followers through to more serious ones) I do think that the even the 996 and Boxster service schedule on oil changes (such as the Porsche dealer low mileage service!) are not frequent enough, let alone the 997, 987 Boxster and Cayman 2 yearly idea.. My reasons for not thinking this is good enough, goes beyond just how bad the oil is after two years, but also covers how many expensive faults could be nipped in the bud as inexpensive repairs with more frequent inspections.

But.. the reason for this post is to say that what Barry has said is 100% on the ball, but it really is not as frequent to suffer terminal engine damage as some may believe, a lot of owners have bailed out of Porsche ownership fearing the engines are hand grenades waiting to explode, but in reality, I think they are no less reliable than any other engine.. I am sure some specialists of other Marques will agree that every engine by every manufacturer has a way they can terminally fail and when they do, they fail in a similar way on that model.

BMW's had an issue of bore issues.. My friends and I have had BMW's of that engine type without any of us suffering that issue back in the day.. all in all..

the internet is a wonderful thing, but I think in reality, if as many engines failed D-chunk as the internet would have people believe, with the volume of M96 engines out there, every specialist would have one of each engine variation on the shelf and ready to go.. Hell, if I knew I would need one of each type on just a yearly basis, I would keep them in stock.

So, if you have one of these engined cars, stop worrying.. If you have suffered failure then I really do feel for you, you have been really unlucky, but the good news is that it should never happen again... I have not known of a Hartech engine re-failing, and I have not heard of a factory replacement engine failing (although more likely than a Hartech one)..

Back in the day, the 3.4 996 and 2.5 Boxster were known as "ones to avoid" as at one point between 2002 and 2008 they seemed to be the ones that had issues.. But, now they seem to be the most reliable ones.. Which makes me think, some engines leave the factory destined to have a life of under 60,000 miles... Once they got past that point, they seem to live a long life, as do those that have failure and have a Hartech or Factory replacement engine.

Anyway, just my opinion.. I personally have 3 Porsche with watercooled flat sixes, and other than changing the IMS Bearing for an updated one whenever the opportunity crops up, changing the thermostat for a cooler one, I don't expect any of them to suffer a failure... I think they are more likely to get t-boned by someone than they are to suffer engine failure with the right maintenance.

In the words of Hitchhikers guide to the galaxy "Don't Panic!"