Uh Oh, Bore Picture and Question

[nuvolari]

I posted pics of my engine bores when I first disassembled it and was reassured that all was completely normal but today I noticed that the mark in the bottom middle of the photo feels rough. It feels like a raised abrasion and not necessarily a recessed or scored roughness but it is tough to tell for certain. However, the rest of the cylinder is completely smooth and then this roughness is quite noticeable.

So, is this the dreaded bore scoring? Or could it be where the oil ring gap has caused a roughness? And is there a solution short of throwing the entire engine in the garbage for either problem? Or is it something else entirely.

Arghhhh....

Second pic is the markings I'm asking about, circled and magnified for clarity.

Engine is a 2000 3.2L, cylinder #2.

[nuvolari]

Better pics added:

[JFP in PA]

Looks like the early stages of it:



Could be time to re-sleeve the case..............

[elgyqc]

I only know what I have read... but I have read more than once that bore scoring starts at the bottom of the cylinder.

[husker boxster]

Originally Posted by elgyqc

I only know what I have read... but I have read more than once that bore scoring starts at the bottom of the cylinder.

It did on my CSS. The thought is the cyl is too short at the bottom and too much of the piston is exposed below the cyl at BDC. When it heads back up for the compression cycle, it rattles a bit before it fits back into the cyl. The rattling means the piston and cyl are scraping against ea other, which wears the coating off each and starts the scratching effect that worsens with more cycles because it's alum on alum now.

I thought I had some pics of my #6 cyl but I couldn't find any. The shop that confirmed my BS said there was a thin crack developing in the cyl and would have eventually chipped off a section if I'd ignored it. And this was on the bottom of the cyl, so I couldn't see that from on top with my scope. The scratching had gotten so long I could see them with the piston down, but you don't see the worst part from above since it's hidden by the piston.

[The Radium King]

are there multiple mechanisms that induce bore scoring? i understand the concept of lateral thrust on piston walls due to the overboring and longer stroke used to increase displacement. in these cases the lateral force would be greatest at the bottom of the stroke. and also why scoring typically presents in the higher displacement m96/m97 variants.

but what about cylinders going out of round due to high temps/oil failure?

https://www.rpmspecialistcars.co.uk/porsche-bore-scoring/

presume less common as this would be an o&m issue vs design issue, but might be the cause of scoring on the lower displacement boxster engines? in this case the scoring would happen where the out of round is the highest which would be top of cylinder where oil distribution was lowest/heating the highest?

[JFP in PA]

We are dancing around the semantics of how many angels will fit on the head of pin here; the simple fact is that the bore in the photo is scored, and in a very bad place near the top of the bore where it will impact ring sealing. So whether it is "classic" bore scoring, foreign object scoring, ring land failure scoring, or dark side of the moon scoring; the fact is the bore is scored and damaged.

The larger question is what is the OP going to do about it?

[The Radium King]

Originally Posted by JFP in PA

We are dancing around the semantics of how many angels will fit on the head of pin here; the simple fact is that the bore in the photo is scored, and in a very bad place near the top of the bore where it will impact ring sealing. So whether it is "classic" bore scoring, foreign object scoring, ring land failure scoring, or dark side of the moon scoring; the fact is the bore is scored and damaged.

The larger question is what is the OP going to do about it?

not sure if we are dancing around anything? your first response wasn't very definitive - "looks like it". so, with only some pictures to go by, as well as a few dissenting opinions, i don't think a discussion on potential causes is out of line. it is certainly not a semantic discussion.

if you want a discussion more 'semantic' in nature, how about the difference between scoring and bore polishing:

https://www.rpmspecialistcars.co.uk/app/uploads/2020/03/M96_M97_GTPorsche-Cylinder-Bore-Scoring.pdf

[The Radium King]

here's the hartech take that shows the difference between polishing and scoring ...

911uk.com - Porsche Forum : View topic - Identifying bore scoring - with photos

[nuvolari]

And the plot thickens....

This is the other side of cylinder #2, the same cylinder.

All of the other cylinders except for the 2 with the pistons at TDC are perfect with no problems whatsoever. The mark in the pics below is rough, so I'm assuming a gouge.

What's the cause? Is this a broken ring?

Argh, only one way to find out, unfortunately and expensively, so I guess I'm tearing the crankcase down and looking to find out if the piston is damaged and the condition of the rings.
Of course, my main question here is if I could use this block as is with the other parts replaced or if once scored, will it only continue to self destruct? And of course I can already guess the answer to that question but all opinions appreciated.

[nuvolari]

And now wondering if a better sounding and much more reliable engine (Alfa Romeo 24 valve V6) will fit in there.....?

[The Radium King]

busso!!!

probably too tall.

[nuvolari]

Originally Posted by The Radium King

busso!!!

probably too tall.

https://youtu.be/WqPyF_BtV64

have you seen this series? Audi 4.2 V8 into a 986! And straight bolt on to the 986 tranny!

[The Radium King]

nice to dream about but packaging and mechanical connections are just the start (presume custom bellhousing or adaptor, even if you went with the more modern holden v6 they put in the brera ...). gotta get the ecu to talk or running a whole new dash, abs, fuel controls, etc.

it looks like a little piece of your engine (ring?) did a tour through the cylinder on the way out. dunno if that is something you can ignore or if you are on the rebuild/replace decision journey ...

[Gilles]

Originally Posted by nuvolari

And the plot thickens.... This is the other side of cylinder #2, the same cylinder.

Nuvolari, have you tried to clean this with a rag with acetone?

[Radman]

This seems like the perfect opportunity to put a rebuilt 911 engine in. All depends on how much you love the car itself. You could also rebuild this motor and make it a little bigger.

I've looked at the audi or chevy conversions but those are still a ton of $ to do it right and most do seem to have some trade-offs.

JMO. The second my 99 motor shows signs of issues it's gone and we'll save up to put something more fun in it lol!

[Newsguy]

Originally Posted by Radman

JMO. The second my 99 motor shows signs of issues it's gone and we'll save up to put something more fun in it lol!

My thoughts exactly! 3.8 here we come!

[elgyqc]

For me the question is... is it going to get worse and destroy the engine? That scratch looks to me like it happened as an isolated event, something was in the cylinder, made a scratch and left. If it had been there for more than one stroke it seems to me it would have made multiple marks, in straight lines. As for the other marks... who knows. If someone has taken apart engines, noted minor anomalies, put them back together and run them I would love to know the results.
If it was my engine I would likely put it back together, forget what I saw and keep a close eye on the oil filter for metal shavings. But then I tend to be a shade tree mechanic.

[husker boxster]

Originally Posted by elgyqc

For me the question is... is it going to get worse and destroy the engine? .

"You can't stop him, you can only hope to contain him!" - Dan Patrick from his ESPN days.

Bore scoring starts because the coatings on the cyl and piston skirt have been worn off and you're left with alum on alum, and that doesn't go well. Once it starts, you can't stop it but if caught early you may be able to slow it down (see Jake's video series). But chances are you'll be unaware of the coatings wearing off until it's too late. It doesn't take long for it to get so bad it's drinking oil like a drunken sailor and finally the knocking noise arrives. By then it's too late.

[nuvolari]

Originally Posted by JFP in PA

The larger question is what is the OP going to do about it?

Yes, that is the question....

Still trying to decide and figuring the additional cost for disassembling the crankcase. And that's without touching the actual damage to the cylinder. But I am sure about that problem meaning that I'm not going to resleeve or buy an LN block simply because it is just not worth it. If I decide not to risk the block, then this car is probably going in the trash. However, seeing as I already have almost all of the parts needed to reassemble it as is but with new and refreshed IMSB, AOS, tensioner pads and the usual gaskets and seals, I guess I'll do that.

I have posted this same question on Facebook M96 Engine Gurus and Lee Jenkins of Hartech seemed to think it's not so bad and just put it back together and drive it. (I suppose the best thing to do would be to put it back together and NOT drive it! Ha, sorry, M96 joke....) However, it's almost hard for me to type that solution as I really feel like it's a ticking time bomb. Yes, I know, all M96's are time bombs but in this case, it's ticking faster!

I really want to see what shape that piston is in but don't want to pay for ARP con rod bolts, more gaskets and seals and probably the internal tensioner pads and arm and whatever else I'm forgetting like rings, etc. Is it dumb to open a case and not replace all the rings? I suppose it is but what do you guys think?

Of course, the problem with new ARP parts and rings is that if I then use the same block, there is still a great deal of worry about whether it will be ok or not. Although, maybe by seeing the piston, I will be reassured or possibly enlightened by the damage. In other words, if the piston skirt is fine, then it may be worth risking a reassembly. However, if the piston shows damage and scoring of the coating, then this engine is finished.

Is it possible to see the piston skirts at all with the cylinder at BDC? Do they hang out the bottom of the cylinder at all? Probably not enough to see anything, especially on the part of the piston I want to see.

So I guess the question to me becomes, "Do you feel lucky, punk?" And, no, I do not! Luck does not work with these cars and I have to say, with the other cars I have, it does! Probably due to the year of production as my other cars are 70's and 80's and not meant as another M96 slam, but these engines do need more precision and don't appreciate cutting corners which is fair.

So what do you guys think? If you had a couple thousand more dollars budget, what would you do?