STL-996-955TT

I own 2004 955S with 205k miles; been battling with miss firing and on #6. It sounds
like my engine; it will get louder and see flakes of silver in oil filter at 180k miles. Go with TT model. They don’t have the same block design and has piston oiling holes.

Charles Navarro

All models have an Alusil engine block including the GTS, S, and Turbo, so they can all suffer from bore scoring.

The VR6 based V6 models have an iron bore so scoring is a non-issue with those engines.

Later Panamera, Macan, and Cayenne -6s that have a Porsche based V6 (not VW VR6) also are Alusil.

I presume that Porsche will eventually move everything over to SUMEbore which will make scoring a non-issue like with Nikasil bores.

STL-996-955TT

Unless you work at Porsche parts counter and can show me 955 S and turbo blocks have the same part number. I will believe other info sources.

Jfrahm

Instead of sleeves, liners or a coating they cast a block out of high-silicon alloy and then use a caustic paste to etch the aluminum away from the bore surfaces, leaving a glassy surface that the piston runs on.
https://en.wikipedia.org/wiki/Alusil...ring%20surface.

Charles Navarro

These engines all feature Alusil engine blocks. There is no coating on the bores. The pistons have an iron clad coating. Here's the document right from Kolbenschmidt with regards to the Alusil engine blocks used in V6 and V8 Cayenne and Panamera (and later Macan) models:

https://www.yumpu.com/en/document/vi...-v6-v8-kspg-ag

As this thread pertains to piston slap and bore scoring, any engine featuring an Alusil engine block can and do indeed score, however not as often as engines with Lokasil engine blocks (i.e. M96/M97 engine).

J'sWorld

Haha, internet call out Charles! What a fool. But seriously whats with the valve guides in these things, they seem to wear fast. Phosphor -bronze? Whats your solution?

TomF

Okay... I usually don't go do this route... but why are you here if you don't want to listen to a group that has a serious amount of combined experience? This is how misinformation gets spread on the internet-by posters with one or two posts that assert that the world is flat.

Charles, thanks for chiming in.

Charles Navarro

As we all know, guides and rod bolts seem to be problem areas Porsche just can't get right. Just look at the most recent recall for proof of this.

I'm not a cylinder head guy and for sure I can't comment on guides on the Cayenne, but on the 9A1 engines the guides are too short. I've seen longer guides made and fitted which greatly help.

I know when we pulley my 14,000 mi 2010 Cayman S's engine apart to build Cayman X's 4.2 liter almost 10 years ago that the guides were completely shot. There were probably 50 hours of track time on that engine from what memory serves me and the engine had short oil change intervals with good oil (not M1).

MrLu

Hi mate, I have recently acquired a 2008 Cayenne S and if you read the forums long enough bore scoring will sound like an issue that is extremely widespread. I have spoken to the Porsche specialist who said that they personally have not seen a 957 with a bore scoring but they have seen plenty of 955s. It doesn't mean that it never happens to the 957 but I guess it happens to a lesser extent. Check out this link - you'll see what an actual engine with bore scoring sounds like. It is in Russian but the point is I think your car is absolutely fine and it doesn't have bore scoring.


Cheers,
Nik

ekstroemtj

As this thread pertains to piston slap and bore scoring, any engine featuring an Alusil engine block can and do indeed score, however not as often as engines with Lokasil engine blocks (i.e. M96/M97 engine).[/QUOTE]


maybe this is now a stupid question....

why does it happen usually only with one or two cylinders? I have never seen a broken engine where all cylinders where suffering.
Is there a statistical number, which cylinders are “most sensitive “ for this issue?

maybe it’s written already somewhere but I didn’t find.

t

i have seen already many damaged blocks. I suffered also from a scored engine some years ago.
Cold start In the German mountains at -25 degrees.
end of the story . My mistake. I didn’t start and drive right away. I left the car idling because it was so cold. Very expensive mistake.


thank you for your attention

hopsis

Maybe the progression of scoring is so fast that once it starts at some random cylinder, it goes from bad to worse rather rapidly. That would result in the knocking noise and soon after that, loss of compression, misfire, and illuminated cel which then would result in someone taking a peek in the cylinders. Just guessing here.

quight

From what I've read, it seems to most commonly effect cyl 8. 1st hand experience aligns.

Charles Navarro

I have several observations I have made over all these years.

We don't see scored bores very often in Boxster 2.5, 2.7, or 3.2 engines. These all received cast KS pistons, not forged mahle. The iron coating is much more durable on the skirts. I also believe the piston to cylinder clearance was too tight on the forged mahle pistons.

Porsche did not have bank specific offsets until somewhere around 2012 or 2013 (I can't remember exactly), which means on one bank you end up with increased side loading of the skirts. This is my opinion why they score worse on one bank than the other, however we have seen scoring in all cylinders.

On the M96/M97 engines with the 82mm stroke, the pistons come out of the bore 7mm at BDC which I think also makes the problem worse with the 3.6 and 3.8 models. I have never looked at a Cayenne to see if this also is the case.

Injectors going bad and washing the bores down is another element we've seen and this is likely caused by ethanol enriched fuels.

Lastly, long drain intervals with oils formulated to improve fuel economy rather than reduce wear add to the issue.

It's not one thing alone that contributes to bore scoring - it's multiple things coming together to form a perfect storm.

Davebrossi

Cylinder 8 was the culprit for me. I saw some cross chatter about block heaters for the ambient temperature issue a while back, but with so many variables here, uncertain if that's a way to mitigate some risk. Granted I'm self interested in this case, not quite a dry sump.

ekstroemtj

Thank you for u your note. Not necessarily.

my Porsche shop has a client who is driving around with a tick tack engine already for more than 35.000 km