Giovanni Giovino 6.0+6.0TT

[QUOTE=born_slippy;24930871]Hooooly crap that Bentley rebuild must have taken you all weekend. QUOTE]



"Weekend" , I wish, many weekends and late nights, still at it, getting close !!

03_AR_CO

One hell of an undertaking, my hat is off to you sir. Let me know if you have any advise on changing the head gaskets on the A8 W12, looks like I am heading that way. Coolant may not have been up to the task for a cold snap we had here in CO. The car sat for about 6o days out in the cold. When I started it up, I fogged the neighborhood, and and was losing coolant, although nothing on the ground, nor under the car after putting it on the lift, no visual evidence of a leak. My car was originally an AZ owned car, never checked the coolant capabilities. Think it slightly froze past the head gaskets. I have a misfire on cylinders 2 and 11, can't be cleared for long. I'll be doing a leak-down test in the next week or so to try to zero in on the trouble.

Giovanni Giovino 6.0+6.0TT

Hello 03 AR CO,
I understand what you are thinking, but may I ask have you yet to check the coolant mixture, because regardless of cold or hot climate, you would still have anti-freeze/anti-boil coolant in the system, you hopefully have a coincidence going on, when I received my 05 A8L W12 from the west coast it was a gallon and a half low on coolant, turned out it was all the pin holes in the small black plastic coolant tubing, I also had some misfires and did the coils, plugs, coolant sensor, hoses, filters, brakes in that weekend as seen in my old thread.

Hopefully you do not have a head gasket problem, but if by chance you do, the head gaskets are available, but that is it, there are no torque specifications available for the W12, BUT Jason Giannetti in West Babylon NY has his shop and specializes in Lamborghini, Ferrari, Porsche, Bentley, so if and when you do have the unfortunate failure of a head gasket, Jason has rebuilt Bentley W12's from the bottom up, and I am sure he would share he secrets of torque specs he devised himself and have been proven tried and true.

See my link for W12 coils, plugs, coolant hoses and plastic tubing..

https://www.audiworld.com/forums/a8-...t-day-2852419/


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03_AR_CO

After reading low on coolant, I filled it up again, ran the car and coolant level ran low again after 20 minutes of run time. I do appear to have steam coming from the exhaust. Believe me if it just the head gaskets I would be happy at this point. Hoping no bent valves or other damage. The leakdown test will tell me a lot about what is going on. We were close to 20 below for a while while it sat, hope nothing cracked, but really does seem like the head gaskets at the very least.

MP4.2+6.0

Too bad to hear. From having dealt with many a head gasket on the C1 that used to eat them about every 50-70K just for kicks, the shade tree diagnostic I learned after many a head pull was just to start by just pulling plugs. If you are doing compression/ leak down they are coming out anyway so use them for visual diagnostics. There is the old look for milky oil one too--which I had only once--but then there is the basic gasket blow out from combustion chamber to water jacket. In that case when you pull head, you find the steam cleaned combustion chamber. But along the way, you also find...the steam cleaned spark plug. Sounds like your first suspects are 2 and 11 from the codes. Many of my combustion chamber to water jacket ones also meant the coolant overflow bottle would constantly bubble, and sometimes blow up from pressure if cap couldn't handle it. Thus water went into cylinder(s) on motor shut off with pressurized system, restarting motor pushed it out exhaust (assuming no hydro lock...) and then it would be the steam cloud for 20 minutes or more evaporating it off. You could smell the antifreeze in the cloud vapor too BTW, though the Audi stuff doesn't have a strong smell out of bottle.

I have to believe any head pull on a W12 is probably a motor pull anyway, but maybe GG knows. Seems like it to get at the timing chains on back--to free up the cam drives to pull the head. I did many a head gasket in vehicle, including front belt driven C5 4.2, but probably not to be here. Would be helpful though to get some comfort only on one side and hopefully confined to gasket. Plug pull might inform some there. Ultimately probably still guesswork if coolant really froze in motor without a complete teardown. Even then not sure you would even find some inside the head type cracks given modern lost sand and other casting techniques, plus the W12 heads are so wide and complex with the VR6 siamese cylinder layout.

Amiko Tsanava

Hello.

I have pulled out W12 6.0 engine from my 2005 Audi A8 and conducting some repairs.

Does anyone know measurements and specifications of the piston rings?
I'd like to replace them and need to know precise original measurements to find new ones and compare them to the factory data before doing anything.

Any help would be appreciated so much.

Thank you in advance.

Giovanni Giovino 6.0+6.0TT

​​​​​​Hello @Amiko Tsanava,
I am on holiday at the moment, but when I return 1-15-21 I will look up the buyer of a Bentley W12 block that I sold not to long ago, he used the block for his 2005 A8L W12, and he purchased new pistons and rings from a company in Germany, iirc.

Johnny

Amiko Tsanava

Many thanks!

I have measured the pistons and they are okay.
I'll have to replace the rings only.
your help would be appreciated!