Advice please on 996 borescope pictures

Hi all, I’ve recently bought my first Porsche (2003 996.2 C4). I see it as an ongoing project and have invested in a mid rise lift so I can access it properly. One of the issues I wanted to look into was it smoking on startup, clear when warm and no “ticking” noises. I understand the cylinders were relined at some point in its past, I’ll look through the invoice folder later to see what more I can see on this. Anyway I’ve taken out the plugs on Cylinders 6 & 5 and taken some photos with an iPhone based scope. Both appear to have oil pooling at the bottom of the cylinder at the head end. I can see cross hatching on what I assume are the liners but these have been replaced by vertical lines at the bottoms of the cylinders. I’m assuming this means oil is leaking up past the piston rings probably where the vertical lines can be seen. I guess this is a sort of bore scoring but if the liners are made of a tougher material than the original cylinder walls then maybe nothing to worry too much about? I’m assuming that being a flat 6, valve stem oil seals are not a likely culprit on this engine? Any thoughts, views or opinions greatly appreciated.

Looks like classic bore scoring to me but i'll leave it to keener eyed and wiser members to weigh in.

Looks like bore scoring, but I’m no expert. Had mine inspect last year, they looked totally clean, so yes I would be looking further into this

Thr flared images require further investigation where it looks burnt on the cylinder wall, , but the other images look fine to me

If it was my car I'd do an oil change to something like a Millers 5W50 (that is what I use in wifey's 996.1) and see how you get on, it could be that the oil is very thin. I have a 964 and that did an smokey start about 50% of the time but a change of oil (10W60) reduced the frequency of oily startups to probably 20% at most. It is so easy to over think things and fear the worst but those images don't look that bad in my view, however I'm not a pro mechanic - just an over thinking anxious old guy.

The cross hatch pattern in the photos indicate steel sleeves have been installed. The factory bores do not have cross hatch marks. Without knowing what work was done previously it's impossible to say what method was used (steel sleeves pressed in or complete machining to remove the old bores then replaced with steel liners), but those pictures look typical for steel bores. Bore scoring was likely the cause of the rebuild in the first place.

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Thanks that confirms my thoughts. Liners were apparently installed in 2013 (about 20k miles ago)following a strip down due to snapped Intermediate Shaft. Work was done by Tower Porsche so I’d assumed steel liners rather than some Hartech type replacement. I don’t know if steel is likely to deteriorate faster/slower than the originals, I assume dechunking is not likely though?

Some owners have reported issues with steel liners moving after a rebuild, a quick seach will show the details. D-Chunking is a different failure, it could still happen after steel liner inserts installation but unlikely now given the age of the engine. A steel bore surface would be considered more durable than the factory Lokasil as long as the mating parts (pistons, rings) are compatable.

They don't look scored to me. What oil are you running and how long since it was changed? Do you know if the AOS has been changed? How full is it? Try and keep it around 3/4 on the dipstick, just in case it is at max and you are getting some oil getting sucked into the aos. My car is rebuilt using ductile liners and I can get a bit of oil in my cylinders, seems to be less as the miles rack up on it. My rebuild used a low tension piston ring, so I will get a bit of blow by (oil passing the piston rings and getting burnt). But I don't get any smoking. I just change my oil every 4-5k miles or so, to keep it nice and fresh. It looks like you might have a bit of glazing in those cylinders. Maybe it was not run in properly using a running in oil, or not for long enough? I wouldn't worry too much. I would put in a nice 5w50 or 10w50 and take it for a few good blasts and see how you get on.

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Thanks for taking the time to respond. I’ve only had it 3 weeks but it looks like it’s had regular annual oil changes the last few years. It is still on Mobil 0W40 though so I will be taking your’s and Jed’s advice and going for something thicker though can’t decide on 5w50 or 10w50 yet. I’ve no evidence of the AOS being done but I’ve checked filler cap for vacuum and whilst not with a manometer it didn’t feel like much vacuum on it. I also took the air box off and had a look inside the throttle housing, there was a fine mist of oil on the inside surfaces but did not seem too much. I’ll probably do it soon anyway though. Oil level was full when I picked it up but it has since dropped a little so I’ll keep an eye on that.

You might just have some oil getting past the piston rings if yours is rebuild, they often use a low tension ring with a slightly higher tolerance when using ductile liners. Just top up the oil every few months. 0W40 is probably too thin for a rebuilt engine, I run 5w40 in the winter, but as the ambient air temps start to rise I move to a 10w50. I have really liked the Motul oil, but the 5w50 Power is a sort of hybrid between the race oil and street oil, and my car was consuming that quite quickly. The 5w40 much much less. I have got 10l of the Motul 8100 5w40 sat here and 5 litres of the Motul 8100 10w60, when the ambient temps start to pick up I will put 5 litres of the 5w50 in and 3.5 litres of the 10w60 and see how I get on. What is your oil pressure when the oil gets hot, like 100ºc hot? If it drops below about 1 bar I would be going to a thicker oil. And does it get to 5 bar when 90ºc plus when you get to 3500rpm? If not definitely go a bit thicker.

Piston's by Capricorn. BTW Capricorn at their Basingstoke facility can also re-nikasil plate cylinder bored that are not too scored. I don't know if you knew that. They can do it to alusil liners too to avoid the necessity of replacing should you wish to. Enabling you to retain std size bore and pistons. The caveat is that the damage is not too deep.Their plating is to Motorsport spec, not production car spec.