2001 996 3.4 Bore Ovality vs Scoring

Options, Options, Options�. I have an engine that came with a car I purchased; it looked a little worn, but nothing major that would raise it to the level of a �bore score� based on the pictures I�d seen online. What I did find after measuring the cylinder bores to the best of my abilities at .0001 is that upper ovality is more of an issue than any bore �score�. It caught me by surprise, as most people don�t seem to talk much about this when discussing the risks of these motors. I�ll see pictures of people asking if X amount of scoring is okay when it�s similar stages to mine, and the response is that it�s normal wear, when in fact it�s likely quite out of round like mine. Another interesting note is that they are all like this. All those cars running around 75k+ miles running fine also have ovality. I also have watched many rebuilds online that don�t bring this up, possibly because they knew it was running fine before, they just want to avoid the discussion, or just don�t know to even bother measuring it. I was looking at getting my pistons recoated as they looked a little worn, so I started measuring everything. Unfortunately, I got the motor as part of a project, so I have no idea how it was running before I got it. It had an IMS failure that impacted the heads/cams, which is what I focused on tackling (and did tackle in another thread). What I�m looking for is some opinions/options other than dropping 10k on Nikkie�s. I grew up around restorations, and I can�t say I have the emotional connection to the car to warrant going upside down in it. It was more a project to scratch the itch of wanting to work on a Porsche over the summer here in AZ, and I thought I�d gotten a pretty good deal on it. Options I�m aware of LN Engineering Nickies / pistons ~7-8k + tax Second-hand short block/motor (likely has same exact ovaling wear issue, but rings and pistons are untouched and hopefully still sealing better than mine that has been taken apart) Hone and re-plate, not sure where this is done / if it�s a decent option Steel or Iron Sleeves - not really a bit fan based on what I�ve seen online PS, the massive zoomed-in nature does make the cylinder look a bit worse than it actually is. There's nothing to catch a nail on or anything like that. Thanks!

How many miles does the car have? Is it stick or auto? Is it original paint with no accident history? I assume it doesnt have any rare options like sport seats or X51? Im just trying to assess what the car is really worth and whether or how much upside down you would actually be.

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Manual with no accidents and 68k miles on the car. Interior overall is in great condition, except the bottom of the sports seats is dried out / cracking. Exterior is in decent condition; it needs the front bumper resprayed due to just discoloring at a different rate, and it came with a black rear bumper as it went MIA when the car was abandoned. I currently have a quote for $1050 to paint both, but I may need to also add those little plastic rails on the roof if I want to really finish off the exterior perfectly. It is not the original engine or trans, as it was abandoned in ~2021; I sourced a trans from an acquaintance that had similar mileage. Engine I have no background on, other than it came with the car, but didn't belong to the car. Thanks

Sounds like you are looking or a cheapo way to rebuild an M96 with "out of round cylinders".. About 7 years ago Hartech in the UK used to offer a "support ring" for the top of the cylinders...You would "jack" the cylinders back round and machine and install a support ring to keep the cylinders round ( within a 0.001 OOR ) ...Then recoat the pistons skirts and hone the cylinders with a special procedure for AL/SI.....I have heard there are hundreds of M96 running in the UK with this but they have since started replacing the entire cylinders with Nikasil lined Cylinders ( like Nikies ) and new pistons..... Note::: Nikasil doesn't even require a coated piston skirt .. Also be aware you may not find a machine shop to do such a repair...I'm sure I could convince a machine shop to do this by taking all responsibility on myself and double checking their work, but you may not be able to convince a machine shop to do this.. I really wouldn't recommend this procedure but is just a FYI if you want a Cheapo way to get your car on the road ( assuming you are keeping it and not passing it on without full disclosure )...but like I said I have heard there are hundreds in the UK running with this type repare .. The " proper " way to repair is to replace all 6 cylinders with a Nikasil or more robust liner so OOR is not an issue ..

This has some info on the OOR numbers. https://rennlist.com/forums/996-foru...ml#post8847349 Not sure if repaired cilinders with relevant mileage have been opened up and info shared to confirm that also OOR wear is solved with them but LN/Flat six undoubtedly will have made sure that is the case.

I believe Porsche still sells short blocks. Costly up front but the core exchange will get the price back to a decent level. Do you know anything about the cylinder head condition? That would be a go/nogo for doing a shortblock. You also still have the while-you're-in-there stuff. (WYIT -- I think that's an acronym...)

Throw it together and run the hell out of it until it actually stops running then trash it. That car isn't worth dumping money into, but it's still worth beating the **** out of.

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And that is also the proper way to repair bore-scoring. Really, if you do not want spend money on it, put it together and go tracking with it. If you want "working on a Porsche" experience (you mentioned this somewhere), nikasil it and sell it to get your money back out. I don't have the feeling that you are attached to this car emotionally enough to keep it long term.

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His journey started with a head rebuild! The low cost option is getting it back together as is. I saw Jake Raby�s reply to this post of FB, recommending reusing old rings if the bores aren�t fixed. That jives with the �drive and enjoy� you are finding in here. Jake also issues a bit of a warning that you faced an uphill odds without heavy work. I think trying a coating only and reassembling with old rings and bores, or coating bores with Millenium Tech or similar and doing piston coating and new rings are probably the lowest cost solutions available. MT coating might be the best cost/risk, while Nickies would be better technically, but at higher cost. If you do old rings and bores and get it back together, if it runs well and you put 10k miles and a few oil changes on it with no ill effects I think you could sell it in clear conscience. But if it eats itself you will be headed to MT or LN and another pricy gasket set, and a month of weekends or more. That�s my 0.02, but I have less experience than you pulling these apart, just a lot of research. My car is high miles, 195k, and needs engine out service, but I would prefer to enjoy it further as a recent purchase before sinking more money into it. No doubt I would be in the same boat as you if I pulled the pistons out� so I�ll do what I can to keep everything around them healthy (timing, UAOS, oil sump, etc) and running as long as I can, and when the time comes, hopefully I can reuse all the fancy bits with a more reliable core� either re&re�d on the cheap or punched out to something exotic, depending on when that time comes! If you are trying not to be upside down on it and enjoy the work, try out some of the simpler options and see what works. Just don�t pretend it works if you learn that it hasn�t. But in the meantime, you might be able to withdraw some �good-times� equity. These are a riot even just in fair health.

One thing to note not yet mentioned on this thread... When excess OOR/Taper are found in the m96 its not from normal wear and tear like most all other engines that develop OOR/taper. Its from cylinder structure failure. The cylinder in simple terms is collapsing into itself. The binders in the Lokasil are failing and the silicone particles are coming out of structure. This problem can and does manifest itself not only in very excessive OOR, but in cracked cylinders & D-Chunk'd cylinders. All cylinder structure problems discussed by the m96 experts in detail. Excess OOR/TaPER is possibly the cause or at least 1 cause of piston slap/rocking in the bore that leads to/accelerates bore score. From what I've read/seen, bad bore score is always part of excess oor/taper. Some over .010"+ OOR/Taper. Kind of like a houses failing sinking foundation. Until its fixed the house will never be right... Until cylinder structure is fixed no band-aide will fix the 'foundations' problems... That being said, sure you can clean it all up best as possible, reassemble it all, and it will no doubt still run, maybe acceptable to some at least for a little while. Hey, I've taken apart other type engines with both top rings busted in pieces, cylinders worn badly, but engine still runs. Maybe not a quite, no oil use powerhouse, but its amazing at what an engine can withstand and still run. I've heard/seen boxster m96 engine run for months with the loudest rod knock I've ever heard.... That just goes to show how beefy the reciprocating parts are built on the m96. Guess the bean counters didn't get to the rod/piston/crank R+D dept... jmho

There is no 'binder' in the Lokasil. It is the aluminium alloy of which both engine case halves are made of (cast), that the silicon is embedded in. Another train of thought regarding the cause for cracked cylinders & D-Chunk'd cylinders is a failed AOS, where full vacuum (high revs, throttle butterfly closed) is inside the engine and oil is sucked into the cilinders in such an amount that cilinders hydrolock and crack or even d-chunk. @OP how much OOR are cilinders 2 and 4 at the top, at upper compression ring level?

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You mean like this ?? VVVVVV ... Multiple cylinders D-Chunking at the same time ( hydrolock from weak AOS ) ...

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Dumb question, but where exactly would that land? I measured about here for the top:

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I'm definitely leaning towards either MT with cylinders or just coating the pistons if possible. Debating the cost benefit, I'm not really worried about my time; I think it's more if I get it together and it has **** compression, I have to pull it all apart again, and what cost does that incur? I would love to do Nickies via LN, but I don't think I would recoup that and would end up upside down. I have a company that I think does a similar process to MT over here called EBS Racing, with similar prices. I've only seen them suggested once, though; vs MT, I've seen them all over. Someone on Facebook responded that they recently got a quote for about $1k per side of the case, so $2k-ish for the honing and plating. If they can also do the pistons at the same time, that seems like a reasonable option, and I may also recoup some of it when I go to sell, vs just doing the pistons. My other worry is that I've not assembled one of these together before, and if I mess it up, I'll be extra peeved I blew the money on cylinders. I'm sure shipping isn't cheap, though. I was just in Oshkosh for the air show right by them, and would have packed two extra suitcases with the case halves on my trip if I'd have known I needed them at the time.

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It's closer to the 2nd ring but no reason to repeat measurements (although that is always a good idea as it improves accuracy). The upper ring goes to where you see the carbon (the little bit that is left) reaching down into the cilinder.

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Keep in mind I'm not a metallurgical engineer, and am just repeating IIRR, what I've read in 100's of papers out of the UK on this subject years ago. Written by m96/lokasil experts Harteck and Kolbenschmidt. By all means do your own research, as I might have not fully or accurately described below the full Lokasil story... but it is to the best of my old memory... Even lake Speed has some interesting articles on Lokasil. IIRR he explains why Lokasil is "localized Alusil." vs true Alusil fully cast hypereutectic aluminum. lokasil's uses a silicon-rich 'preform sleeve' only placed 'around the cylinder bores' with a binder holding it in place. Lokasil = "localized" hypereutectic aluminum technology. A resin binder is used to hold silicon particles together in a temporary, 'freeze-cast' sleeve pre-form. Then molten aluminum is injected into the casting, the heat supposedly burns away and replaces the resin. Thus leaving behind only a high concentration of silicon particles embedded directly into the aluminum cylinder wall. In many m96 cylinder walls, the binder didn't 100% burn off, leaving microscopic voids and remnants creating a non uniform matrix. Then over time and use, with added mechanical and thermal degradation of the resulting metal matrix, leads to cylinder failure. And most diffidently yes to AOS doing the finishing touches on cylinder walls that are already weak and defective. On most any other NA engine, when engine hydrolocks it bends rods, shatters pistons, not busts off a D-Chunk piece of cylinder wall. That seems to mostly be a problem of our weak cast localized hypereutectic aluminum cylinders . jmho

If I do MT, does it make sense to bore it out to a larger size than the stock size? I'm not sure what other costs I'd incur if I did that other than the pistons. Do I need reprogramming, beefed-up anything else, etc? What is a reasonable size to go up to? I'm going to give MT a call this afternoon. Thanks, Taylor

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That is a lot more accurate. Thanks for taking the time to respond.