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Discussion Starter #1
Hi everyone, I recently bought my V10 after a long time of consideration and search. I’m already a bimmer guy but this is my first non old schooler (maybe not so new),and for the last couple of months of ownership I’m already dealing with some issues.

Tried to find some similar cases on the forum but nothing popped up (sorry if I missed anything)

Well, I bought a 2007 M5 with low miles (37k). I sent it for a check up as soon as it arrived and it had a leak on the steering rack only. When it was at the mechanic I already changed the oil for precaution.

When ready, went to took it home and a couple of miles on the way I saw a huge amount of smoke coming from the back.
Stopped right away and I was able to see that it was coming from the left exhaust, specially when running (at idle it was almost not coming any smoke out)

Took it to the dealership and they want to disassemble the top of the engine cuz they assume it is the valve stems. I checked the forum after some similar problems but didn’t find any.

It really seems like the valve stems cuz it reminded me of those e90 320i that puffed white smoke, but since I didn’t see any other topics related, I was wondering if anyone had any issues with this?

Besides that, Last week upon startup on the dealer came a loud humming noise (very low pitch), not a ticking sound or like that, is more like a constant “uuuuuuuuu” coming from the engine bay. The dealer wants to disassemble the guide chain and tensioners cuz it suspects its coming from there.

Honestly I’m very confused, I went to the dealer expecting a more direct diagnostic, but since they want to dismantle de engine apart to check what’s happening, I’m trying to find any material on similar cases to avoid any unnecessary services.

Anyways, hope anyone can help me with any insights or experiences on any of the issues.

Tks!!
 

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First, welcome to the board.
It sounds like your shop/dealer/mechanic are confusing their experiences: Unlike the M/N6X series engines, valve stem seals and chain guides are not common failure/wear points on the S85. Furthermore, the symptoms you describe are not typical of valve stem seals: when valve stem seals leak, the smoke tends to be the worst when idling for extended periods, with most smoke produced upon first throttle application after this extended idle. you may be familiar with this depending on what motor you have in your E53.

Where are you located? I would recommend finding someone local to you with a bit more experience with the S85. Dealers tend not to have this experience.
 

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I'd add that depending on what color smoke you had and if the engine was running rough you could have a partial stuck open injector. Now this is a not too common failure but deadly for these engines. Likely due to a failing fuel filter that leads to debris on the injectors. Deadly because it can hydro-lock the engine resulting in bent rods, cat fire, etc.

The 'uuuuuu' noise is likely just the air pump running during a cold start routine.
 

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Discussion Starter #4
Tks for the reply, the car is running great, didn’t had any issues on running or idle expect the smoke.
I couldn’t see very clearly but it appears to be white smoke. The injectors are quite new (only 2k miles), not sure about the filter.

Since I didn’t found any material on this kinda problems anywhere, that’s why I’m not so convinced to let the dealer just open it up to check what’s wrong.

In my area the dealer is the most recommended place, but I have 2 guys couple hundred miles away that already had experience with the s85, probably will ship the car to them. One of them told me it could be piston rings, since some of the cara he worked on had similar issues, but again, couldn’t find any material elsewhere to support this and also since the engine is running smooth and no cylinder pressure loss (at least when scanned) I assume it could be something else.

Tks anyway guys, I’ll keep updating it with more info
 

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Cylinder head gasket failure could be another possibility I suppose but I've not yet heard of one going on the S85 especially on one with such low mileage
 

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Discussion Starter #6
Well after some time we opened the engine and found a head gasket blown but also, and more problematic, cylinder 9 has some deep scoring, probably due to a faulty injector.
Hopefully no harm was done to crank and billets but will check. Now, I’m stuck with a difficult decision ahead: hoon the cylinders to increase bore and use larger pistons or sleeving the block.
I haven’t seen any info about scored engines and solutions, anyone with an ideia?
is there any reliable sleeves to this engine? Hooning the engine block requires any special machine due to its components? I’m really in the dark here.
Also, If hooning, Carrillo pistons are a good choice?
 

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Wow... that's very unfortunate - very sorry to hear! Sounds like one cylinder may have been detonating and overpressuring, causing the failed head gasket and scoring.
Being an Alusil block, yes honing requires a special technique to expose the silica particles:

See if you can get a hold of Jim to get advice on this, as he has experience with boring and honing the S85:

 
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