GC996

Does anyone remember the early on discussions 20 years ago about how the early 996.1s were prone to "D Chunking" due to how the cylinders were held by a clamp during the assembly process. The ideas of "hydralock" or "broken water pump fan" wasnt something we ever discussed.

Then the issues with the frailty and limitations of the oem AOS processing oil flow took center stage. Porsche developed the Motorsports AOS as a more robust but expensive solution to the oem AOS. In Porsche's infinite wisdom, they also recommended running less oil to protect the factory aos. At that same time, solutions for on track oil starvation were also developed, imsb solutions were developed and Porsche finally found a RMS that worked after replacing countless engines.

Today, the next round of improved AOS and oil starvation solutions have been developed with more iterations on the way.

It became common knowledge back in the mid 2000s that you didnt want a factory AOS if you were canyon carving or tracking your car because you not only ran the annoyance of blowing smoke and oil consumption, but you also ran the risk of intermix and yes, cracking your cyclinders which also includes "D Chunking" from hyralocking. Seems that D-chunking in the early 3.4s may have had nothing to do with the clamps used in the assembly process and instead, it may have been caused by AOS failure (hydralocking) and a broken water pump blade that gets lodged in the engines causing cracking. Same for the 3.6. Go figure.

I agree with those that say the 3.4 and 3.6 are very durable engines. Mjne has shown this to be the case. But history shows they can be easily improved upon and be made even more durable with just a couple of relatively inexpensive parts and procedures.

If you are a talented DIY guy, you have alot more flexibility and willingness to judge the fix/don't fix decision point due to your skillset.

But if you are not a DIY guy, you have to make a decision on what to upgrade or replace and when, depending on your philosophy of "proactive" vs "reactive". But let's face it, there are three parts that can go in the blink of an eye that can lead to catastrophic engine failure. (1) IMSB, (2) AOS, (3) broken water pump blade.

It's everybody's call on whether they want to do something about it or not.

Haalex

You mean nothing better than spending 25 grand on an engine that runs well?

GC996

Unless you don't mind it being 50 hp low and always on parked on the side of the road.

zbomb

What do you mean 50 hp low ?

You're just making that up based on your vast non existent experience, right…

I gotta give you credit, I have never seen anyone on a forum speak so conclusively about what to do and not to do with so little actual experience, remarkable.

Your experience begins and ends with writing dudes checks to work on your car changing stuff they tell you to or what you read people talk about on the internet and somehow that makes you an expert in all things M96.

I think what it really makes you is an Indy mechanics wet dream.

GC996

Karen, time to take a nap. You are getting a little over excited again.

Haalex

I started by saying he should dyno it, so....

hkovalcik

gc do u think I could poop-a-lock my car if I blew a sh*t into my throttle body?

GC996

I haven't tried that one yet.

brontosaurus

If you can accurately poop one teaspoon I will uhh

I am not sure what the correct reward is for this

Icelia

Thank you everyone for your passionate advice.

I would of course prefer to not put any money into the engine and drive forever... But we all know that is a pipe dream.

Next oil change (a couple of weeks from now) I will get in there with a camera and take some good imagery of the crank to IMS chain tensioner and wear pad. That will answer the question of if I need to split the block.

If I do have to split it, then I would carefully ensure that the rings don't rotate on the piston when the piston is out of the cylinder, so I can get them back in their exact position again.

As long as it isn't burning oil or have any scoring, I see no reason to re-sleeve. If I felt that way, I might just buy a blown engine and do it all while still driving this car, and then there would be minimal down-time.

I have every confidence that the car will keep going to just fine past 200k if I do nothing... Im not looking for an excuse to spend money, but I have some plans for some very long cross country trips, and I want reliability above all else.

So I think investing a few thousand $ now will extend the life of the engine and keep me from worrying about reliability in the middle of 6,000 mile trip.

Thank you. I will update the thread again when I get some imagery of that tensioner.

allcool

While it sounds feasible, once you pull the piston out of the cylinder, past the normal travel of the rings, the ring expands past ring groove/leyland. Most older piston grooves get a wear 'step' the ring seats into. Once ring expands it will never go back to how it was in the piston or cylinder. Rings normally rotate on the piston when running unless they have locator pins.

Is there a chance rings will reseat once you pull them from the cylinders, yes. But its a big gamble thats up to you to bet on. Just go in knowing you might have to rip it apart again in a few thousand miles....

jmo

Marv

You could always do an oil analysis and leak-down tests if you want more information on current condition, but I would not be too worried about high mileage, especially if the previous owner was fastidious about maintenance..

As a general rule of thumb I would keep driving the car if it is running well. You wouldn't get an organ transplant if you are healthy, even at an advanced age.

The exception might be if you are planning something like a long trip or other event where you absolutely need to mitigate and reduce risk.

hardtailer

If rings normally rotate when the engine is running wouldn't that mean that they will continue to do so once put back into the same cilinder on the same piston?

I believe only the oil control rings have a pin on the M96 to never have the ring gap end up at the low side of the cilinder where oil invariably would collect when sitting. However, the 1st and 2nd compression rings can rotate AFAIK.

allcool

Ya, you'd think so...

Just not sure ring rotation has much to do with re-seating old rings/pistons in out of round tapered cylinders. Even when matched up to same cylinders they came out of.
Never really heard a good explanation of the 'why' this never seems to work out well.

My guess is it has to do with the ring groove in the piston and the old ring getting relaxed and then re-compressed in a worn stepped piston groove. Thus not being able to cope with/seal oor cylinders. Seems to be a very fragile relationship good sealing old oor cylinders have with their pistons/rings. Any disturbing of this 'relationship usually proves to be not satisfactory.

But thats just a guess... I know In the distant past (never on a m96) have tried at least a dozen times to seat new/old rings/pistons in worn out of round/tapered cylinders with no longevity ever. Finally, even at a tender young age, determined must be a good reason manufactures have a max out of round taper spec....

Icelia

If the bores are out of round, then the rings can't rotate.

All this is making me want to open it up less and less. Damn the design which does not allow the tensioner wear pad to be replaced without disassembling the entire engine!

I don't want to drive to catastrophic failure though,

If the tensioner is on the verge of failing, then maybe I will end up just doing a full rebuild.

I'll know in a few weeks.