Cylinder #4 Dead. Please Help.

My driver side exhaust was pouring out burning oil smoke so I decided to pull the engine and transmission. This is a 2002 C2 with manual transmission. I scoped cylinders 4,5, and 6 from the spark plug holes. 5 and 6 were in pretty decent condition. The spark plug from 4 was covered with oil and oil was pooled in the cylinder. The pictures show plugs 4 and 6. The two different oil pooling pictures shows how much oil was added after I rotated the piston one revolution. The last picture is a strange marking on the cylinder but not really the same as typical bore scoring. Do you guys think I have a broken ring in cylinder 4 or could it be a valve leaking? Should I start tearing down that side? Thanks in advance.

I wouldnt start tearing the engine down just yet. Is there any oil in the intake manifold? How old is the AOS? Did the exhaust smoking happen all of a sudden or gradual over time? If it's pure oil, that means the head or the cylinder sleeves likely have not cracked.

Yep , sound like your AOS failed and you narrowly escaped hydrolock!!! Cut the AOS diaphragm open and see it has split before you dive into the engine..

Same happened to my 02...AOS Failure!

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Wow. Extreme.

The AOS is supposedly brand new(dealer repair) from the paperwork that I got with the car. I believe it�s considered a sport version and costs almost $1000. If It�s bad why would it dump oil right into cylinder #4 only? It seems to be gathering more oil in the cylinder just by one rotation of that piston without even running the engine.

Do a compression test.

2nd gear is shot also or I wouldn�t have pulled the engine and transmission.

What happens with hydro lock?

This is the reason I designed the UAOS and the blow-by test procedure. Hydrolock happens when over 60cc of oil enters cylinder #4 and locks it bending the Rod or cracking the cylinder!!!

Can you point me to more information on UAOS and the blow-by test procedure? Thanks.

I found the information on the UAOS. Will it work with this AOS? The engine is out with no oil in it. Is there any way at this point to determine if this is what�s going on for sure? I could connect the starter to power to do a compression test but I think doing it without oil is risky. I could also put oil back in it. I didn�t really want to cut a $1000 AOS apart in it wasn�t necessary.

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First thing is to see if the $1000 AOS has failed. The Porsche Motorsport AOS has a diaphragm in it that can fail just like all the others. Send it to me and I can test it without damaging it or cut it open. The reason oil goes to #4 cylinder is oil is heavier than air, the plenum behind the throttle body is biased toward bank 2 and #4 is the first cylinder of bank 2. In the meantime you can do a leak-down test of the cylinders instead of a compression test, and you wont have to "spin" the engine.

BTW, AOS's have been known to fail brand new out of the box, just sayin. I agree with Prelude Guy and PorscheTech's diagnosis, and if it is a failed AOS its a stroke of luck for you because that's the easiest and cheapest (unless you go with another $1K AOS) fix for you, and you caught it before you hydrolocked the engine. Best of luck.

Fyi, the uaos is designed to work with a $79 aos if u have to replace it. i know it doesnt make sence but several here have been through this so take the friendly advice and wisdom and determine the state of your aos before spending a lot of time and money.

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Yes, also the UAOS warning system ( watchdog ) would have alerted about this condition..

So after getting into the intake and not finding much oil I scoped the cylinder again and the marks on just cylinder 4 look really strange. After looking at some piston oil rings I realized I had just seen that pattern before. If you look at the last picture of my original post you will see it on the cylinder wall. The leak down test showed the same as the other cylinders but I think that mark shows the oil ring broke. What do you think? Thanks.

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Looks like carbon streaks to me, from carbon breaking off and getting stuck between the piston and cylinder wall. Similar to these pics except worse. Does your black streaks go all the to the top of the cylinder??

I�m not sure if they go all the way to the top of the cylinder or not. There are 8 or 9 perfectly straight marks that look like the same spacing as the oil piston ring grooves. I assume the only way to know for sure would be to rule out the AOS and then disassemble the engine. Unless there�s a trick I don�t know about to inspect the piston rings.

If your intake is not full of oil inside it is not your AOS that has failed. A thin layer of oil is normal inside.

Bad news for me. That�s a picture of cylinder number 4 broken off at the bottom. Do you think I�m better off trying to find a used engine or replacing 4,5,6 engine block? Would a sleeve for cylinder 4 be an option? Thanks.

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LNE can fix it if the crack is not extended beyond the cylinder and into the case, they machine out the complete cylinder and even have a procedure to repair the lower cylinder support area. The cases are a matched set and can't just get one side case..Sorry for the bad news.. They would machine out all 6 cylinders plus machine out the lower support for cylinder 4, as long as the crack is not propagated into the main case area. Don't know what the cost would be but it's 5k for all 6 cylinders with pistons then the additional $1k or so for the lower support repair for cyl 4, but you'd have a good reliable repair with new pistons. I had a feeling if those marks were from the oil ring something would have to gone way wrong to break an oil ring, now we know the chain of events..

If it were my car, I would spend money on a factory short block.

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I'd ship it to LN Engineer for nikasil bores. Personally, I wouldn't go the Porsche short block route. You end up with another engine with Lokasil. Just my 2 cents.

Does anyone know if the stock pistons are forged? Thanks.

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Manual says they are cast aluminium. Might be cam ground as well. Iron coated for sure.

I may have spoke too soon about you "narrowly escaping hydrolock". That may have been what set off the chain of events on this engine. A failing AOS that caused a mild hydrolock that bent the rod, then the bent rod broke the lower cylinder on #4 which caused the oil ring failure. You will know for sure when you get the pistons/rods out and inspect for straightness.

The rod seems straight but the piston is damaged. Does anyone have a stock piston they would sell that would work in this 02 3.6? Thanks.

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is that a serious question? Its not really how it works with these motors.

Yes. That is a serious question. I am having the block repaired and sleeved. I need a decent piston to work with. The other 5 are in good shape.

U r not having any work done to the other bores? There r a lot of things that need to be checked on these cyls because ovaling is a big issue. I guess u might have got lucky and randonly only had one bad bore, but thats usually not the case. Also pistons r usually a matched set. not trying to be a dick or anything and there is a lot of doom and gloom on the board but there r also more then a few threads on failed rebuids due to quick fixes. I guess fo your research, form your own opinons and make the decision that best fits your situation. Good luck.

I am definitely going to have the machine shop check my other bores and pistons. They are visually in really good shape(175k miles). If I get lucky and it�s just the one sleeve I only need to get another decent stock piston. The sleeve will actually get bored according to the actual measurements taken from the replacement piston. So at this point I�m hoping someone has a piston laying around and is willing to help me out. I can only go one step at a time from what the machine shop is telling me. The guy there has been doing excellent work for me for the past 25 years.

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Like De Jeeper, no intent to criticize or offend. $900 gets you a new set of matching pistons and rods from LN Engineering (I wouldn't even think of reusing rod #4 or an unmatched set of pistons) and with 175k miles, you'll be dealing with other cylinder issues sooner than later. Think about going the Nickies route for $5,100 and never worry about bore scoring or d-chunk again. Heck, even take a look at Hartech cylinder replacements that Alpine Autowerks can do (Calgary, AB). At the end of the day, it's your car and $$. Just trying to give some friendly advice from experience.

Also one thing to point out it steel cylinder replacement in these motors may not be the best idea. There r several theories/opinions and even rebuilders with a lot of evidence that supports steel in this aluminum block is a bad idea. Again, be informed and make the right decision based in facts and your budget. Ultimately and unfortunately there r not a lot of reliable low costs solutions to this problem.

Thanks for the warnings but I�m willing to give this a shot if someone has a piston they are willing to sell. I do trust my machinist and if it doesn�t work out I�m not against dropping the engine to start over. Either way I will post what happens and how it turns out.

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whether you trust your machinist or not is totally irrelevant - he may be the best machinist in the world, but if he�s willing to put 1 steel sleeve in a M96.02 motor he clearly knows little to nothing about them... Good Luck

My machinist did say if the press fit sleeve from cylinder 4 effects 5 then I would have to sleeve all three on that side. I was just being optimistic with one sleeve. Most likely I will sleeve 4, 5, and 6. Still hoping someone will help me out finding a piston. Thanks.

This might help , I know ideally you should used a full matched set of rods and pistons but if your budget doesn't allow this , you might be able to do as you are thinking and replace one rod and piston but make sure you weight match the rods and pistons to within , 1 gram tolerance , your machine shop should help, porsche make piston sets and rod sets in weight matched groups and there is variation I.e some sets may be heavier or lighter as a set over a period of time with production tolerances so using a piston from day eBay may come from a different weighted batch and might be out of spec with the set of five you still have but I can't see a problem if they are properly weight matched and material is removed from the correct areas of the piston/rods to make a full matched set, there are areas where weight can be safely removed, we are talking a few grams here! So I would say although in an ideal world where money is no object it would be nice to have a full set of nickies and a set of wossener pistons, I think as long as you make sure everything is in tolerance weight wise and the piston you get has intact skirt coating, which is very important , don't buy a piston with any marks on the skirt or any sign of the skirt coating wearing away , it must be pristine, it's the most important part of the piston to look at plus any obvious signs of damage from an engine failure like where a valve has hit etc, some people may disagree with my reply but I'm trying to help with the road I think your going to take ! Good luck ? https://www.ebay.co.uk/itm/174004633539

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How much are you expecting this sleeve job is going to cost?

In the famous words of the Meineke Man - "You can pay (me) now, or you can pay (me) later..." Paying later is more expensive...

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This is so true, do it right and do it once. My mother's family's motto has always been "if you can't do it half-a$$edly then don't do it at all." I've always hated that mentality. It always costs a lot more in the end if you try to just get by now. I think @Byprodriver has an M96 motor with Nickies for a fair price. Or talk to @Charles Navarro about an RND motor. It'll cost some but you'll have a strong running engine in the end.

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That rod needs to be replaced. Crankshaft also needs to be magnafluxed.

Hey Noz. Thanks for the heads up on the different weights of the pistons. It looks like they came in two different weights. That eBay ad was in the uk and they don�t ship to the us or that would have been perfect. I�m still looking for a used oem piston and I will make sure it�s in the correct weight range. Any other leads on a piston would be appreciated.

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This isn't a small block (Chevy). The M96 engine case is delicate, just to put it mildly. Too much press fit and pop, the block cracks. See it all the time. I've seen plenty of blocks with single holes sleeved or just one bank. Usually something else goes awry sooner than later.

Thanks for the heads up. I will pass it on to my machinist. The value of the car doesn�t justify dumping ridiculous money into it. So sleeving is my best option at this point. Do you think starting a new post looking for a piston is the best way to find someone on this site that might have one?

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Ebay or one of the dismantlers (several sell on ebay). There are different bore size groupings as well, so you will need to make sure the piston is sized the same as your other ones. Ideally you want less than .0005" difference in skirt diameters between the pistons. Although this is for the Cayenne, it applies the same to the M9X engine when evaluating the condition of the pistons and block (see attachment).

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I'd sell it as a roller if you're not willing to rebuild it right, then find another having a proper PPI done. It's going to be a buyers market real soon!

Duke Hartech in the Uk can repair one sleeve , but they are not just any shop they are probably the best in the Uk on the M96 and have developed their own cylinders etc, the cylinders are similar to Nickies so are not ductile iron but proper Nicosil played aluminised sleeves , they will be able so sort you a piston aswel and you will have no worries about them wrecking your block as they are specialists on this engine and highly regarded, they do work on overseas stuff, might be worth a call to speak to Grant , he's a top guy!

After pulling this thing apart and looking at the damage it doesn�t really make sense to me. What could have caused this? There was no impact damage to the chunk of cylinder that broke off. The rod isn�t bent so it didn�t hit it. If it hydro locked it would have bent the rod and damaged the top of the cylinder. Is this just a fluke or something that normally happens to these engines?

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O-M-G... Duke/TJ?whatever your name is... with all due respect, go do some reading dude! You're asking questions that have been covered at least 100 times on this forum as well as others. While there are lots of helpful folks here, it gets really old after a while. Just look up D-Chunk and you'll have a couple hours worth of reading material. The engine doesn't have to hydro-lock to have a d-chunk failure... it seems like you're already having second thoughts about Porsche (at least M96...) ownership. Sorry about your experience - it definitely sucks. Education is your best tool right about now

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I think his problem is quit unique !! D-chunk usually happens at the top of the cylinder (his chunked at the bottom) Bottom cylinder damage is usually from a broken rod smacking the cylinder at the bottom. I still think his rod is slightly bent (even though it "looks" straight) and that is what stressed the cylinder at the bottom. It would only take a few thou bend to cause the piston to overstress the bottom of the cylinder due to the piston acutaully comes half way out of the cylinder at BDC. Need to do precision measurements of the rod straightness. If I interpret Charles Navara's comment correctly, he thinks so too. IF the rod shows a bend of just a few thou, I would say for 100% sure it was caused by hydrolock.