Opposer

9a1 on a base cayman 2.9 doesn't have DFI so there can't be petrol leak from injectors to the cylinder.
does this fact significantly reduce the probability of bore scoring?
2.9 is also a low-displacement engine
i found only one case of bore scoring in 2.9 in the Internet, on a 9k mileage.

silver_tt

9A1 is DFI

https://lnengineering.com/products/w...html?limit=all

Charles Navarro

The base 2.9 does indeed have port injection, but you can still have leaky injectors or poor atomization which can wash the cylinder bores down, just like we see with the prior generation of engines.

Opposer

but with a much lesser probability?

Charles Navarro

Yes, I would expect it to be less, but how much, I can't say.

steveP911

Here is my story.

History
• 2005 997.1 C2S purchased in Spring 2016 with 46K miles.
• No bore scoring examination done during PPI. My bad.
• Had cylinder leakdown test done Fall 2020; all cylinders less than 10% drop.
• Normal oil consumption of one liter per 2-3K miles, or better.
• No exhaust smoking noticed, and soot buildup not noticed since tips are black.
• Began doing 5-6 HPDE events per year two years ago. Car is now >80% track and <20% street.
• Oil consumption about one liter per event. I have been told that is "normal".
• Had AOS replaced last fall since trailing driver noticed a white puff on one of my shifts. Did not do a manometer check at oil filler before replacement. Now it reads about 5.5” of water (good).
• Have committed $$ into track mods, including a significant amount this winter.
• I have been using Liqui Moly 5W-40, changed every six months since tracking, but annually before that.
• Added 1/2 qt sump extension Spring 2022.
• Installed 71°C thermostat Fall 2021. Installed center radiator Summer 2018 and installed screens in front of all three radiators. Fall of 2022, replaced left front AC condenser and cleaned/cleared other side plus all radiators.
• Currently 67K miles.
• I do not hear any tapping sounds and I do not see any exhaust smoking at all.

Bore Scoring
• Just had borescope (through the sump) examination as part of other service/upgrades. Yes, I should have had this done before, and certainly at the end of track season, not the beginning. At least I had the scope done before this set of winter mods, in case the findings were really bad. See photos in next post.
• Cylinder 4 spark plug was pretty fouled (all will be replaced).
• Oil was dark, but not unusually so.

Moving Forward
• Based on my copious reading about this issue (which is what led me to have the examination), the markings “appear” to be early and limited enough (obviously IMO, but same as my mechanic) that I should not be in immediate danger of engine damage outcomes.
• Plan is to go through this track season and carefully monitor conditions each day. Will change oil after first event in March and send to Blackstone for evaluation. Will then use Driven racing oil exclusively after that (not 100% sure which of their grades – DT40 5W-40 or FR50 5W-50?).
• Since I really like my car and the track, I am not contemplating selling it or stopping HPDE. I want to determine my best rebuild option for Fall 2023 (season ends last weekend in October), hopefully allowing time for the rebuild plus break-in before the start of the 2024 season. I would like to have some direct interaction with Charles Navarro since my plan at this point is to use LNE for as much as possible, including other upgrades (maybe even 4.0). I’ll need to find a local shop that I could trust to do the whole engine out/in process.

Questions
• Am I being too optimistic? Are these photo indications serious enough to warrant an all-stop?
• Any advice on the rebuild process? Ideally, I would hope to have it fully accomplished within a four-month window. Is that reasonable?

Thanks very much,
Steve

steveP911

Cylinder 1


Cylinder 2


Cylinder 3


Cylinder 4


Cylinder 5


Cylinder 6

Charles Navarro

For an engine with stock Lokasil bores, 1 liter in 2-3k miles is a bit high and 1 liter per track event is a bit much, but I've seen engines go for a while longer even at these levels.

I think you are good with running the engine a bit longer as-is. It's not making a lot of noise and isn't burning tons of oil, so I think you can use FR50, DT50, or DI50 until you take it off the road for a rebuild.

Carreralicious

Wait, 1 liter per 2K-3K miles oil use is a bit high? What about the cars that burn at a rate much more than that that don’t have scoring? There are 997s that burn at a rate of a quart per thousand miles and are at over 100K miles already.

Charles Navarro

At 100k the cylinders are out of round and that's probably what is contributing to the oil consumption, especially if the engine is running M1 0w40. I'd expect these engines to have low manometer readings below the 4-6" which is normal for a healthy stock engine with stock AOS.

Engines with Lokasil and Alusil bores tend not to burn much oil, if any at all, until there is something wrong, and then consumption will increase exponentially. This is different from Porsche engines with Nikasil bores which have always averaged about a quart in 1000 miles, which is normal.

The amount of consumption is not in itself the issue, it is the rate of change of consumption. I have a 2006 VW GTI that has burned a quart of oil every 750 miles since day one. It has 140k on it now and finally it has settled down to a quart in 2-3k. :-)

Carreralicious

Ah ok. Strange cause I know of one Rennlister off hand who bought his 06 997S new and it was, and is still burning a qt per 1000 miles since new to now at over 100K. But I get it…watch of any drastic changes to oil consumption. Thx.

Charles Navarro

Although that is under Porsche's max oil consumption spec, I'm guessing there was something wrong with the oil rings, perhaps they had slightly lower tension which would contribute to higher consumption. Nothing that would cause a failure.

Jake measures ring tension on every build to make sure the oil controls are where they need to be as they can vary from set to set, right out the box.

OutlawCayenne

New guy here I have a 996.1 and I just bought a 2006 CarreraS with known Bore scoring the car is a Canadian car but west cost Vancouver island so not overly cold weather. It currently has 76,000km on it. It looks like only about 1,000km/year for the last 5 years so I assume the scoring might have been noticed back in 2018 and definitely the last few years the car has had minimal mileage and seems to have passed through a few owners over the past couple years. It puffs a lot of smoke on start up and although I have not put a lot of miles on it yet myself it seems to burn a decent amount of oil and a very audible tick. I am going to change oil before I get to driving it a lot and monitor consumption I was hoping I would get the summer out of this engine and swap it out in the winter but the piston slap if pretty loud so I am not sure it has a summer left in it.
any suggestions for oil or oil additives to help me squeeze the last summer out of the engine.

Charles Navarro

About the only thing you can do at this point is put thicker oil in it - something like Driven's FR50, but that's a band-aid at this point if it is already very loud and consuming large quantities of oil.

PV997

Hi Charles - I've long believed the root cause of M96/97 bore scoring was failure of the piston skirt coating which leads to galling from aluminum (piston) on aluminum (cylinder) contact. There are lots of other contributors but ultimately I think it's the piston skirt coating flaking off that starts the ball rolling. It's also not just some scratches that's a problem but specifically aluminum galling, as that is what causes the ugly, unstoppable cascade. Seems like we are relearning some of the hard lessons of early aluminum block engine rebuilders regarding the importance of skirt coatings.

I noticed Jake had a livestream about two weeks ago where he discusses piston coat flaking (which he calls stage 0 scoring) and he alludes to this phenomena with more details to come in future videos. Looking forward to it.

What has me concerned is that the skirt coating flaking may be related simply to time (i.e. the coating becomes brittle with age) as opposed to mileage (wear). This could mean low mileage cars are just as susceptible as high mileage cars. Unfortunately, there's no easy way to inspect coating condition, all we can see are the results of it (scoring) and then it's too late once galling has started.

Following that same line of thinking, that means every M96/97 owner should assume their piston skirt coating is potentially compromised and the only thing preventing aluminum to aluminum galling is the motor oil. None of this is new thinking of course, but that would mean all M96/97 owners should follow a prevention list (along with rationale):
.

• Frequent oil changes (to guard against viscosity break down)
• Use the highest viscosity oil that's appropriate for the car's operational climate (to ensure adequate oil thickness/viscosity at the thrust face)
• Use oil with high levels of moly or a moly additive at a minimum (as moly is well known for it's aluminum anti-galling properties)
• Install a low temperature thermostat (to reduce temps at the thrust face and preserve oil viscosity)
• Never lug the engine (to reduce piston to cylinder sidewall forces at the thrust face that can squeeze out the oil and increase temps)
• Ensure injectors aren't leaking (to prevent fuel wash of the motor oil)

The last one seems more of a theoretical concern to me as the bank 2 thrust face is on the top of the engine. Visualizing this, gravity should help out here as unatomized fuel would fall to the bottom of the cylinder away from the thrust face. This would be more of an issue for bank 1 (where the thrust face is at the bottom) yet we almost never see scoring there.

Any other thoughts on this or additional suggestions?

Thinking more along these same lines, have you noticed the piston skirt coat flaking being more prevalent on bank 2? It's a chicken or the egg question. Do the higher temps of the bank 2 thrust face cause the coating to flake off? Or does the coating flake off on all cylinders but bank 2 is more susceptible to scoring due to motor oil break down?

Always appreciate your thoughts on this and your willingness to share what you've learned.