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.