Secondary Air System Carbon Build Up Removal Pictures - BMW M5 Forum and M6 Forums
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post #1 of 327 Old 11th November 2008, 10:39 AM Thread Starter
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Secondary Air System Carbon Build Up Removal Pictures

Hello everyone. My name is Mert. I'm a fellow board member (recently posted pictures of my car), enthusiast, and also a BMW Master technician. Thought I would share some pictures I took at the dealer concerning the SECONDARY AIR SYSTEM CARBON BUILD UP. This is not a DIY thread, but more of an understanding of the procedure. I cannot give out any information about this vehicle but to let you know this is a E39 M5.

carbon build up does not affect just the secondary air system but also the combustion chamber

exhaust valvetrain

secondary air entry port

rear of the cylinder head with the secondary air port freeze plug drilled out and ready for removal. there are three freeze plugs for the secondary air passages that need to be removed and ports cleaned out

rear freeze plug (#1) removed. pictures show cylinder head upside down on cylinder head stand to perform procedure

special cleaning tool (looks like a rifle barrel cleanng rod). Tool is used with a drill and passed through the secondary air main port.

halfway through the secondary air main port, we hit solid carbon. Let me be the one to tell you, it's like hitting solid metal. Took some time to get though it but we did

after cleaning out main port

this is the front of the cylinder head showing the entry of the main port and also the front main port freeze plug (#2). When looking at the front of the cylinder head, the secondary air pump pumps air into the main port entry of the head then immediately makes a 90 degree turn through a short passage way in the front of the head then makes another 90 degree turn and through to the back of the cylinder head into smaller individual ports to each exhaust valve port

this is the freeze plug (#3) that goes from the entry port through the short passage port to the main port

side view of head showing route of air passage

the smaller individual secondary air ports to each exahaust valve port. the right port in the picture looks to be unclogged, but is clogged about halfway through

removal of carbon with reaming tool and then bristle tool

left port after procedure. you can see the difference in diameter

both ports after procedure

all exhaust valve air ports cleaned out

both cylinder heads are being sent out for further cleaning and inspection. this would be the perfect time to get any cylinder head performance work done.

Hope this helps out.

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post #2 of 327 Old 11th November 2008, 10:55 AM
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Excellent pics! Do you have any idea what the dealer charged the customer for this work? That carbon build up is really bad! I have the same problem and I shudder at the thought of what my engine looks like! BMW really screwed up on this design big time.
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post #3 of 327 Old 11th November 2008, 10:59 AM Thread Starter
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post #4 of 327 Old 11th November 2008, 11:28 AM
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Wow, what pictures!
What a job!
In a nutshell, what causes this problem? bad fuel? Excessive idling? What?


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post #5 of 327 Old 11th November 2008, 11:52 AM
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Are all e39 M5's affected or just the US spec ones ?

Must be very satisfying when you put it all back together and start the engine
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post #6 of 327 Old 11th November 2008, 12:00 PM
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Fantastic post! Thanks for the clear pictures of the secondary air issue as it is much easier to understand now. Given that the ONLY purpose for the secondary air system is cold start emissions, I'm guessing Powerchip is going to be reeling in some income as E39 M5s age.

Thanks again for such great pictures and description.


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post #7 of 327 Old 11th November 2008, 12:25 PM
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Great post, thanks for this..

That build-up looks hideous..

**** it, let's do it - Australian proverb

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post #8 of 327 Old 11th November 2008, 12:28 PM
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post #9 of 327 Old 11th November 2008, 02:29 PM
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Great pics, always wanted to know what it looked like, I hope I never get that carbon build up problem.
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post #10 of 327 Old 11th November 2008, 04:17 PM
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Great post.

Gustav - could you consider adding this to the CBU FAQ?

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