I just had the head rebuilt for the second time this year. I have a Frankenturbo on it with a tune from eTuners. Bone stock otherwise. I drove the car 27K with this setup before the first failure including a few track days and autocross days.
A valve disintegrated in cylinder 3 the first time, spark plug too. I was told there were signs across the bank of lean running. They fully rebuilt the head, all new everything. A month and 2K miles later, very mellow driving, the same thing happens again. This time in cylinder 2. Again full rebuild. They inspected all mechanical elements including function and condition of the injectors. They did a smoke test looking for air leaks. They assure me that everything is in tip top shape, as it was last build. They did take nearly 2 weeks with it vs about 4 days the first time to go thru it as much as possible.
They suggested maybe the tune was at fault. I logged it running on the road, a mix of driving around town, highway speed, and a hard pull or two. Both the installer of tune and owner of the company don't see anything suspect. Saying the results were safe across the board.
I did inquire about larger injectors. The info from both tuner and turbo maker was that there was no need. It is just not that aggressive of a setup.
I'm at a loss, I'm afraid to drive it. Being able to go 27K of occasionally hard driving without a hiccup and then it blows, and then again 2K later? It makes me have to believe there is something going on that someone is missing.

https://www.etuners.gr
http://www.frankenturbo.com/new/F21M.html

 

Intake or exhaust valve? How about the first time? I have an issue with the #3 piston. Funny how it is very often the #3 cylinder.

 

#3 cylinder on my 2008 N14
Oil delivery issue perhaps....when oil is low.

 

Exhaust valves both times.
timski....ouch! I'm def on top of the oil with this thing.

 

Started another thread under R56 to tally up a count on good ole #3 cylinder if you don't mind sounding off on it. Thanks.

 

To the OP:

Do you have any pictures of the chamber?

Were new valves used for both builds? If so, OEM or aftermarket?

What seat width was used?

Where was the seat positioned with respect to the OD of the valve?

How much oil are you burning?

 

I don't have pictures. The dealer did the work, all OEM parts of course. I don't know about any of those specs. It's been a while since I've checked oil use, maybe ½-¾ per 1K? I've been driving monitoring real time AF mixture and it is right on. Mid 14s under regular driving and it gets a little richer if I accelerate hard.

 

Plug in the photo doesnt look like it was getting to proper temp.. there is not 'color' on the insulator at all.

Q - whos gapping your plugs?

 

Extreme heat caused a meltdown, a part of the valve broke off. I was told there was a severe lean condition across all cylinders. Here are what the plugs look like now after a few hundred miles.

 

those look better!

*If you are running a bit on the hot side, may be time for a colder plug to help remove more heat from the spark plugs/combustion area.

 

I'm baffled by the whole thing. Engine temp def not hot and AF mix looks spot on in the logging and observing real time. There's no way it could log correctly, but somehow not be getting the right mix right?

 

any ideas, I'm driving this thing like a little old lady waiting for it to blow up again?

 

Hard acceleration should yield an A/F of 12.5 - 11.8 or so.

There is such a death of information here, one can only guess at the cause of the second valve failure, but guess I will....

First build: Only the busted valve was replaced, its anyone's guess if the seat was recut or not. None of the other valves were replaced or evaluated because the dealer's technician's skill's are limited to replacing parts the diagnostic machines tells them are bad. There is no machine to tell a tech the valve or seat needs replacing/recutting unless there is a big hole in it!. Further guess; none of the other valves were removed from the head for inspection.

Second build: It is possible the head was properly rebuilt with all new valves (intake and exhaust) and the seats were correctly recut and the guides evaluated for wear. Given they failed head rebuilding 101 the first time, my money is that they also F'ed up the second time. Ask the dealer who did the head rebuild (they won't tell you) and what parts were replaced (they may tell you). But you still will have no idea about the quality of the workmanship involved, which is really, really important for head work. You have empirical evidence of this.

Your choices:

1) Pull the head off and take it to a shop with an established reputation for head work (Ask Porsche shops for a recommendation). Con: expensive and may not be needed.

2) Drive until it fails again. This seems like the low risk, low cost option but I am going to take the position that it is not. You got really lucky that the valve chunk did not drop into the chamber or that the valve head did not drop off.
If that does happen there is a very good chance that you'll need a new engine next time. Con: high likelihood of a bigger hit to the wallet than #1

3) Sell the car to someone else. Nasty of course, but real. Con: bad karma....

Wish I could give you a sunnier outlook,but I can't. Best of luck and I hope the above is of some value to you.

 

I'm baffled why it happened in the first place, and more so the second. I couldn't get a viable explanation, just speculation. I've never had this happen in almost 40 years of driving a lot of different types of vehicles. Second could def be due to not a good job the first time I suppose. Log shows A/F getting as low as 11.49 on hard acceleration, if I let off the gas fully and coast in gear it shows 29.9, otherwise mid 14s.

I've attached the invoices with work detail, there are some differences. The first one with lines crossed out is the first time, the other two are from the second.

 

I'm not baffled, but I am disgusted. BMW has a long history of of trying to save some modest sum per car and as a result causing some significant F'up. I don't have time to enumerate all the ones I've observed in close to forty years of driving BMW cars and bikes.

What is clear to me, is that due to the apparently small number of failures, this is almost certainly due to manufacturing defects either in the seat or the valve, or due to using cheap material to save a buck or so per valve. If there were a fundamental design flaw in the head the failure rate would be far higher.

Takeaway from your invoices:

First time:They did no refurbishing of the valve seats at all. Using a new valve on a old seat is bad practice without reconditioning the seat to new condition. It's bad practice anyway, but apparently worse than usual on the N14. The failure to properly recondition the seat affirms my previous statements regarding technician competence.

Second time: They used some lapping paste on the exhaust seats/valves. This is amateur hour. Lapping can never replace seat cutting to restore worn/pitted surfaces. I suggest you confirm that this is the case, and if it is, it is a near certainty that another burned valve is in your future.

The reason seat width, concentricity and angle are so important is because the valves use the seat contact area to cool the valve. If the seat/valve contact is poor, the valve overheats and will eventually burn.

If you do decide to pull the head preemptively, shop around with care to find a cylinder head shop with a very solid reputation. Make sure they have the full picture of the previous work. I would also consider having the exhaust seats replaced as added insurance. And, since you upgraded the tune and turbo, find better exhaust valves than Mini's. I'm not sure what aftermarket options are available, Supertech's seem to get some mixed reviews, and as far as I can tell Ferrea does not make N14 valves at all.

I'm out of time - gotta do a dump run...

Best of luck with it!

 

That's a lot to chew on, thanks for taking the time.

 

I went to see an independent shop yesterday that I found through a listing here. He said it was not that uncommon to see this on a higher mile engine, but... Definitely felt that if the head wasn't sent out to a proper shop to have the seats prepped, in all likelihood that caused the second failure. I'm going to have to go back to the dealer and try to find out if the job was done differently the second go round. They definitely had it much longer.

 

Here's a follow up plug pull. 2400 miles from the last job, and about 2000 from the last plug pictures. Doesn't look encouraging to me?