N62 Extreme Cylinder Wall Damage - Causes?
 

Hello,

I am writing here as this seems to be one of the more knowledgeable forums regarding the N62 engine. This is not in my E53, but is an N62 none the less... specifically a 4.4 originally installed in an E60 manual and now at home in a Z3 roadster.

I have had the car running over 2 years now and the car still runs very well. No misfires, passes compression tests although leakdown tests do indicate something is off.
The only issue is inconsistent smoking out of the tailpipe and spark plugs on 7, and to a lesser extent 8, were always oily. I did the valve stem seals when I had the engine out on a stand, re-did them later on 7 & 8 just to be sure, I replaced the CCV diaphragms then when that didn't change anything I bypassed the CCV system completely with a catch can vented to atmosphere just for diagnostic purposes. None had any effect.

I looked inside the engine with a borescope yesterday, and this is what I found:

Cylinder 8

https://static.wixstatic.com/media/d...abcd73~mv2.jpg

Cylinder 7

https://static.wixstatic.com/media/d...7cad78~mv2.jpg

https://static.wixstatic.com/media/d...93ea2b~mv2.jpg

I did not have a borescope when I originally rebuilt the engine so there is a chance it was like this before I ever installed it. I am going to be replacing it with a 4.8, but am curious if anyone here has a solid idea on what could cause these issues as I would like to do what I can to prevent it in the future.

My main thoughts are the previous owner overheated it (it never overheated in my ownership) or there was, or is, a leaking injector on 7 washing the walls out. I won't be able to dig too deep into it for a little bit but this failure is new to me and I am curious what others think.

Thanks for any input

Middle picture almost looks like the rings are/were lined up, but that bottom photo has a good chance of a broken electrode had been in there.[emoji848]

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Looks like foreign item damage to me for that degree of cylinder wall gouging.

I just inspected the piston top and valves and they show no signs whatsoever of any sort of damage so I do struggle to see how this could be caused by an object inside the cylinder. The damage occurs on two sides of the cylinder wall and if the object moved to both sides, it should also have left signs elsewhere. I've seen engines after objects were dropped inside and it looks awful inside...

After thinking on it and looking at it more, it seems to me more likely to be from piston slap or something along those lines - the location of the damage is consistent with this, being directly perpendicular to the crankshaft and occurring 180 degrees from each other within the cylinder - right where the piston skirts are.
And it's hard to tell for sure but it looks like there are deposits above the surface, not just gouging below the surface.

My current leading theory is something like a leaking injector washed the oil off the alusil coating, allowing the rings to damage the cylinder bore or the friction of the rings dragging caused slap.

It definitely looks like the damage from skirts but probably from being too tight, not from slap. If the engine was rebuilt then for sure the pistons weren't fit properly and/or the bores where not machined properly. You would be hard pressed to find a re-builder that can come anywhere even close to BMW tolerances. Possibly the engine was overheated or run hard cold. Aren't some of the V-8s infamous for cylinder material issues ??

I've been wondering if it has been overheated as well - the previous owner didn't really have great reasoning for removing it to sell and I didn't press him too much, it was a good deal even if the engine is trashed and I knew that going in (came with manual transmission for the cost of just a little bit more than the transmission were going for at the time). I bought it to mock up the swap and always planned on 4.8 swapping but it ran so well I've kept it in for 2 years.

https://static.wixstatic.com/media/d...102f61~mv2.jpg

I think the V8's that you are referring to that had cylinder material issues were the Nikasil M60's.

Make sure to use a minimum 40 weight oil. A lot of the times, lower weights are only for fuel economy only. Thicker is better for used engines.

Initially, I would have said a stuck ring or piston slap from worn rod bearings but that would explain the random gouging. By chance, did an electrode detach from your spark plug in that cylinder? I have seen that happen before. The only other thing it could be is if the engine was rebuilt and steel liners were used with aluminum pistons. They expand at different rates and the piston would expand more quickly than steel and bee too tight.

Initially I thought foreign object damage, and that’s definitely a possibility, especially if those aren’t the original heads. But you’re right about not seeing damage in the head.

Overheating can cause damage like that, but I doubt it would be as localized. As stated earlier, piston slap/skirt are also possibilities. Maybe from sudden engine torque changes since it’s a manual.

https://www.ms-motorservice.com/int/...nd-causes-233/

You covered all the normal oil burning causes and I’d say the gouges are most likely the source of the oil. As to the cause of the gouges, it will probably take a tear down and inspection of the pistons to make that determination. If you do that, please post pics.

Thanks for sharing.

I will definitely share once I get the engine torn down but before then I need to source a replacement.

I went to look at an N62 4.8 yesterday and saw this in cylinder 1. This cylinder also had oil on the plug...

https://static.wixstatic.com/media/d...208d0e~mv2.jpg

It looks to me like this is the beginning stages of the failure that happened to my engine. This was at a local car breaker, so not really sure the history of this engine either.

I do have a 200,000+ mile N62 that doesn't smoke at all so I don't think it affects all N62's, but I am wondering if it affects more than most people realize.

I found this online when researching the topic (page 6 https://lnengineering.com/files/2019...er-Systems.pdf)
The N62 technical manual states the pistons have three rings:
First piston ring groove = square ring
Second piston ring groove = taperface ring
Third piston ring groove = three-part oil control ring

I am wondering if incorrect geometry rings (square vs barrel face) are a contributor to the problem. BMW did use Alusil in other applications prior to the N62 (including the M62 which this issue has not been documented on afaik) - but most the Alusil I6's had iron sleeves...


Still trying to figure out the root cause as best as possible in order to avoid buying a replacement engine with the same problem.

Yeah, my guess would still be something to do with the cylinder bore material. I don't have the patience to read the article but probably some good info. You actually have pitting of the cylinder material, not just scoring.

I recently had a discussion about bore scoring with a an Indy Porsche guy (his shop did a leak down and compression test on the m62 that came out of my x5). It’s very common on some model-year aluminum Porsche motors and their advice is to scrap the block unfortunately.

Has anyone contacted Melling in Iowa?
They used to be good helpful guys and were one of the go to places for sleeving...

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Good call on checking the potential replacement engine! ;)

You said this came out of a manual e60... could that have been initiated by a non-catastrophic money shift? Would have thought that would be more along the lines of scoring than gouging... but I'm a noob to engine internals by any reasonable standard.

A money shift and the resulting burning oil might explain it getting sold. Though I would have imagined he'd keep the 6spd trans unless he scrapped the car altogether.

I have exactly the same wear on my N62B44 on No-8, I can see it from below when I had the sump off for a gasket change

I would say 99.9% this is due to overheating, mine has been overheated on at least 2 known occasions, the previous owner left it running on his drive and found out the electric cooling fan had given up, the tell tale sign was steam coming through the bonnet vents!!

I bought the car with several known faults, it has covered well over 50,000 miles since it developed piston slap because the bore/piston are so worn, it runs on 10W60 and hardly uses any oil, if I run it on 5W40 it smokes like crazy

Im sure ive read about your car on one of the facebook groups, im also doing a Z3 V8 but with an M62, do you have a more detailed write up on it? Would love to read more :cool:

Still looking for a 4.8, but not having any luck so far. Not super urgent either, the humidity this year has made working outside brutal. Normally I cool my garage with an evaporative cooler but those don't work when it's humid...

Generally speaking when an Alusil block is damaged it is time to scrap the block (and usually just replace the whole engine). Alusil blocks can be treated, if scratching is minimal, with the honing paste and felt pads. On my 4.4 I may experiment further, by first boring it via traditional methods, then going to a high grit paste, then the Alusil honing paste. I've read about some guys doing it themselves at home it this way (though never really seen a followup afterwards so idk if it works or not). I don't necessarily plan on running the engine after the work - I just want to see how it looks after for my own curiosity.

There are risks of sleeving, and the even more simple truth is for what a good N62 costs this level of machine work would never be financially justified.

It is very possible it's been overheated, it seems to be the thing most often suggested as the cause. It hasn't been overheated in my ownership, but it makes me think it happened for the previous owner and as it was still running he decided to sell it as-is...

I do have a very thorough, probably annoying thorough and overly wordy, build thread here: https://www.ascfabrics.com/z3v8
I've been meaning to distill the critical information down into a single post but haven't had time. The swap was a lot of work than I had envisioned at first. By the time I knew how much work it was going to be, I was already in too deep to back out :rofl:

M62 swap is much, much easier though - they make swap kits for oil pan fitment and wiring harness adapters - if you gathered all the parts and had everything ready, you could do it in a weekend.

https://static.wixstatic.com/media/d...950290~mv2.jpg

https://static.wixstatic.com/media/d...50843c~mv2.jpg

The sections that look "raised" (circled in green) here are actually flush with the bore material, they look raised because the surrounding material is worn away

https://static.wixstatic.com/media/d...bb5563~mv2.jpg

I didn't learn a whole lot from having it torn down to be honest. I suspect the initial cause was overheating, piston expanding too much and scraping into the cylinder wall.

I'm going to be removing the crankshaft and pistons and I think seeing what the piston on that cylinder looks like will provide a little more information.

Will a 4.8 N62B48(?) work? There's one in Austin for $1000. Seller says working perfectly. It's listed on MP, user Alex Mzhinskii. It has a video and pics. It's on pallet ready to go! Listed from an E70 X5.

You've already seen Sreten's project Chicago episodes?

Seems my earlier suspicions of this being a result of the piston dragging against the cylinder wall was correct

https://static.wixstatic.com/media/d...3360f3~mv2.jpg

And my thoughts that it likely happened due to overheating is also probably correct. All cylinders showed some signs of this occurring

https://static.wixstatic.com/media/d...fcef8e~mv2.jpg

I think what happened is the engine overheated and all of the piston skirts started dragging against the cylinder walls. On most it wasn't bad enough to damage the cylinder wall dramatically, but cylinder 7 - maybe because it was the hottest, or maybe for... who knows why - started gouging into the cylinder. This certainly made some sort of scary noise, at which point I presume the previous owner shut it off. Then they removed the engine and sold it to me, lol


It is annoying that this happened. I rebuilt pretty much the whole engine (sans taking the heads off) and it had no leaks and ran great... it just smoked a lot. It really is quite odd how well it ran given the condition inside here. I think the N62 is a fairly durable engine, even if not always reliable...

But there is a silver lining because I had always planned on putting a 4.8 in there but at some point along the line I convinced myself I was ok with the 4.4 ...now that this happened, 4.8 was the only option. An extra ~30hp and ~50 N-m of torque :D

I will also be working on installing upgraded M62 headers or S65 headers. Once they got here I started to seriously doubt the S65 headers could be made to fit due to chassis clearance, but the M62 ones ... maybe. I'll be using the 4.4 to mock up header fitment and see how it fits in the engine bay

I think M62 headers could be good to get the N62 to ~370-375 and 510-520n-m which is spitting distance to an S62. The stock headers are awful

I already have a 4.8 here

https://static.wixstatic.com/media/d...b69b37~mv2.jpg

If the price was right I'd consider buying a spare but I think shipping would make it cost prohibitive...

But yes 4.8 fitment is the same as 4.4, and can be run on stock 4.4 engine management. Fuel injectors even seem to be the same per realoem

No I have not

Project Chicago. It's about the Alpina supercharged version of N62 but very interesting to see all episodes. Actually this is the other of the only two Youtube channels I follow.

https://www.youtube.com/watch?v=SVM3xeCWuY8&t=1056s