Scouring on cylinder(s)

[Collie]

Hi folks I'm sorry to report that following Bryan Kane, Dublin Specialist, attending to an unusual exhast resonance he heard another noise which worried him and he arranged through Richford,Dublin dealer, to have my car sent to Agnews (Porsche Centre Belfast). Went last tuesday week and news is not good. I had a long chat with Steven B. from Agnews last evening. He thinks it is the above but cant confirm it until engine taken apart . Becuase they are now dealing with entire country and have only one engine table thats not going to happen for at least two weeks, Steven very apologetic but nothing he can do!
Once sure of problem he is going to see what Porsche Factory say re repair under quasi warranty given car's low mileage and service history. Failing that he will look to Porsche UK and if then no poor Richford will have pick up the tab. To be fair Ian at Richford has left me with no doubt he will do whatever is necessary to have the car put right
Anybody know if this is a particular problem to the 3.8 S engine. I got the impresion it was?
The better the case I can give to Steven the better the chance Porsche Factory or UK will pick up the tab or at least part of it.
I have to say I'm disappointed haveing driven 996's for the last 6-7 years with no engine problems or RMS issues that I have this within two months of 997 ownershi[]p
Just looking forward to back driving .
Thanks in advance

 

[snarf]

There have been a few similar reports on the forum, often related to sooty tail pipes (see DrMark's threads), but these were mainly pre 2006 BY cars if I remember correctly. Probably worth searching the Forum for this but beware the search function here often reports negative results when there are plenty to be found - the trick is to play around with the search options and keep trying.

 

[Lancerlot]

ORIGINAL: Collie

He thinks it is the above but cant confirm it until engine taken apart . Becuase they are now dealing with entire country and have only one engine table thats not going to happen for at least two weeks,

Should be possible to tell using an endoscope through the plug holes (if you'll pardon the expression!)
Regards,
Clive

 

[garyw]

Agree with Snarf comments, a few do seem to of had similar failure with prior sooty pipes, however with these things- the numbers do mean you are unlucky to of had this happen rather than it being a common fault.

garyw

 

[bazhart]

You are probably aware that are the UK's leading engine rebuild specialists and whenever a problem is found we analyse it to establish the cause and make a judgement about if it is likely to repeat and what we can do (if anything) to modify or change the parts involves to reduce or eliminate the problem. Consequently we have manufacturerd different IMS bearing parts, replacement liners castings etc, etc with a high amount of investment needed backing up our diagnosis.

Recently we have seen a number of 3.6 and more 3.8 engines with a seized piston - usually number 6 and always from the 4,5,6 bank.

Usually the piston has seized on one side only (not normal practice) and the bores have not yet gone as oval as many 3.4's that are still running OK.

Our anaysis to date has considered two potential causes. (1) that the inlet slots to feed coolant into the block are inadequate for the design (something less than 10% of the coolant passes through the cylinders - the rest - 90% - goes in to the heads). (2) That the extra pressure on the cylinder walls caused by the increased torque at low revs that the bigger engines with variable valve lift - produces - is causing the Lokasil bore finish to break down. Or perhaps both issues combine.

We are doing something to the engines we rebuild to try and change the parameters in case either of those issues is the cause - but it is very difficult for a small business like ours (or any others around the World) to tackle such a problem when it seems such a huge and wealthy business full of experienced and trained engineers, who were responsible for the problem - ether cannot or their bosses don't want them to.

Because the bigger engines are relativley new it is only just feeding down to our level although (just like the original 3.4's) I guess engines have been replaced by the main dealer network for some time - so we get a delayed notice of the problem and a delay in looking into it and it is only recently that enough have come through with the same problem - that alarm beels are ringing. Only time will tell and right now the jury is out - but we are at least trying our best and doing something about it and if and when we feel more confident about the causes we will of course report it.

Baz

 

[garyw]

Thank you for the information Baz, what sort of numbers are you looking at at the moment? with regards to the failures

garyw

 

[bazhart]

Gary, I think that the numbers would not demonstrate very much as newer cars more often have engines replaced within the dealer network and we don't get to see them until the cars are older - when numbers become relevant. I don't see how our numbers would explain anything to anyone else about the bigger picture.

I would guess that we have in the last few years we have seen the number of Boxster and 996 engine repairs increase from one engine/month to three/week (of all models), but whereas the Boxster and 996 engines run at about one Boxster and two 996's/week, enquiries and reports on the Internet about the 997's and the 456 cylinder bank - are at a higher level than anything that preceeded it at the age they are - in the past - and we have repaired three in the last 10 days - so it feels like a premature epidemic and that the best way to compare it to what has gone on in the last few years is to expect failures of these models to exceed the numbers for the previous models - and hence the concern.

It is too early to be specific but there are danger signs that I am simply advising others about - but we must wait and see how things develop before putting numbers to the mix.

Baz

 

[bazhart]

Just thought you might be interested that we have had even more come in the same now. Usually number 6 cylinder and usually siezed on the thrust side.

On investigating further we realised that the entry of cool coolant is on the thrust side of numbers 123 cylinders but on the opposite side on the 456 cylinders. The small nature of the entry coolant slot means that the coolant flow speed will be relativley low on that engine so the temperature rise of the coolant in the cylinder will be relativley high.

Also the oil cooler is situated on the 456 side and the coolant has further to go to get to that side anyway. So everything points to the number 456 side of the engine running hotter on the thrust face of the pistons than the 123 side and of course if that is the problem then that side will seize first.

Although we are trying to rebalance the coolant flow to compenstae when we rebuild engines, I would like to source a lower temperature thermostat as well (if anyone can help) as it may be a step in the right direction and help.

Baz

 

[Gary C]

ORIGINAL: bazhart

Just thought you might be interested that we have had even more come in the same now. Usually number 6 cylinder and usually siezed on the thrust side.

Baz

Sounds so familiar to the Subaru Boxer engine which always melts the same cylinder, but usually a fuel problem coupled with that cylinder being the most marginal on cooling I believe.