Audi Broken Oil Control Rings - Why???

[SonofJoe]

JHogan,

Thanks for sharing your insights as to what happens inside Audi.

Whatever the root causes of this issue, I reckon the problem must be rather complicated. I find it hard to comprehend how the Audi engineers and designers could get this engine so wrong and all I can think of is that several individual things coincided to create one huge, intractable problem.

From what I've seen, there are two distinct phases to the problem. From new, these engines used a higher than usual amount of oil. In this phase, you see oil moving out of the crankcase, through the PCV and into the intake system. There, over time, it would cause very bad inlet value deposits. Ultimately most of the oil gets burnt in the cylinder. Unlike gasoline, engine oil is very difficult to burn. Some of the deposits from partially burnt oil goes out with exhaust but equally some stays in the cylinder, on the top of the piston and down past the piston.

The second phase kicks in at around 50,000-ish miles when oil consumption, which was already high, goes completely off the scale. I suspect this the point at which the oil rings be either stuck solid or break. These are the engines Audi are still fixing.

 

[SonofJoe]

Originally Posted By: edwardh1
again, what changed from the year before?


I think the Audi 2.0L TFSI was a wholly new engine introduced in 2008 and reports of high oil consumption emerged quite quicky. I think I'm right in saying that this was the first high performance production engine to feature both a turbo and direct gasoline injection so it was pioneering stuff.

 

[funflyer]

Hard to tell from the video but it appears that the oil rings have excessive side clearance, noted from when he shows #4 which is not broken and still installed in the piston. Couple that with a thin, weak cast rings and you'll have problems. Wide clearance means the ring dwell time is greater than the piston dwell at both TDC and BDC. Once dirt starts to build between a ring and land that ring dwell time becomes less, not around the entire ring but just where the dirt lessens the gap. When the entire ring doesn't change direction at the same rate the stress will break the ring. Of course, without being able to inspect things hands on, it's just my theory.

 

[SonofJoe]

Originally Posted By: funflyer
Hard to tell from the video but it appears that the oil rings have excessive side clearance, noted from when he shows #4 which is not broken and still installed in the piston. Couple that with a thin, weak cast rings and you'll have problems. Wide clearance means the ring dwell time is greater than the piston dwell at both TDC and BDC. Once dirt starts to build between a ring and land that ring dwell time becomes less, not around the entire ring but just where the dirt lessens the gap. When the entire ring doesn't change direction at the same rate the stress will break the ring. Of course, without being able to inspect things hands on, it's just my theory.


I too had another good look at piston 4 on the video and thanks to you, I now understand things a bit better. Looking at the oil control ring, what I see is a one thin ring and a spring/spacer with a lot of play in the groove. What I was expecting to see was TWO rings, one either side of the spring/spacer, with the total assembly having very little play in the groove. It begs the question was this deliberate design or did they just 'forget' to add on the rings??? There does appear to be space enough for another ring. If they deliberately just went for one thin ring (to minimise friction and maximise power/FE), it explains more or less everything; the poor oil control from the get-go and the fundamental lack of bottom end cylinder sealing. It explains the breakage because of repeated flexing (probably inducing metal fatigue). It also probably explains what Audi finally did to fix things ie put in a three piece oil ring, probably somewhat thicker than the original one.

Thanks to everyone who has contributed to this post. This has been bugging me for ages. For a long time I thought something must be wrong with the oil itself or some strange interaction with fuel dilution. Looks like it was a simple mechanical thing all along!

 

[wemay]

Originally Posted By: SonofJoe

For a long time I thought something must be wrong with the oil itself or some strange interaction with fuel dilution. Looks like it was a simple mechanical thing all along!


I too have serious doubt this is a Noack issue since Audi specs a very stringent oil for their applications. In the video, that engine is clean and appears to have been well taken care of. It strikes me as a design problem.

 

[ryanm8]

Didn't the VW cars (GTI, Tiguan, CC, etc.) of those years have the same engine? I never seem to hear about them having the same issues that the Audi's did.

 

[SonofJoe]

Since my last post, I think I have watched that few seconds of the video where he focusses on Piston 4 about twenty times. I now think I was seeing the wrong thing. Silk had it absolutely right earlier in this thread. This is a one piece oil ring! If you look real hard, you can see the tiny drain holes in it. The serrated thing which I thought was an expanded/spacer for two (or one) rails is actually the tensioner spring that sits behind the one piece ring.

FunFlyer, if you're still reading this thread, can you please flesh out what you said about dirt impacting on dwell angle. I'm absolutely positive you have the answer to this mystery. I just want to sure I have this clear in my mind. Please feel free to assume I'm an idiot in these matters!!

 

[funflyer]

Originally Posted By: SonofJoe
Since my last post, I think I have watched that few seconds of the video where he focusses on Piston 4 about twenty times. I now think I was seeing the wrong thing. Silk had it absolutely right earlier in this thread. This is a one piece oil ring! If you look real hard, you can see the tiny drain holes in it. The serrated thing which I thought was an expanded/spacer for two (or one) rails is actually the tensioner spring that sits behind the one piece ring.

FunFlyer, if you're still reading this thread, can you please flesh out what you said about dirt impacting on dwell angle. I'm absolutely positive you have the answer to this mystery. I just want to sure I have this clear in my mind. Please feel free to assume I'm an idiot in these matters!!


Assuming the ring to land clearance is too loose, which it appears to be from the video, the rings will not change direction as fast as the piston, i.e. upstroke changing to downstroke and vise versa. As the piston drives the rings to top dead center, or the uppermost piston travel, the wide gap between the land and ring is at the top of the ring. As the piston starts on the down stroke the gap is now changed to the bottom of the ring as the ring land makes contact with the top of the ring. The exact opposite will happen as the piston reaches bottom dead center.

Now, when everything is new and clean we can assume that the rings and lands are making contact around the entire circumference which means the entire ring will change direction and start to move at the same time and will have little to no stress induced on them, however, when dirt and debris start to fill the excessive gap between the ring and land, the ring in those areas will start to change direction sooner, just in those areas, due to the gap being reduced. Now the entire ring circumference is changing direction at different rates and subsequently causing more stress on the ring and eventually causing failure.

The oil control rings in the OPs engine appear to be either ductile iron or cast iron which we know are not as strong as the old school steel oil control rings so the ring side clearance becomes that much more critical.

As for the repliers that say the ring end gap is too tight, we should have seen an oil consumption problem early in the life of the engine along with severe scoring of the cylinder walls.

 

[crazyoildude]

these engines are well known in the engine business.

 

[crazyoildude]

JHogan How is Audi about covering this under warranty? Just curious.

 

[Silk]

Originally Posted By: funflyer

The oil control rings in the OPs engine appear to be either ductile iron or cast iron which we know are not as strong as the old school steel oil control rings so the ring side clearance becomes that much more critical.


The cast iron ring is the old school ring, 3 and 4 piece rings replaced them. I've got a BMW V8 apart at work, I was snapping the rings to see if they were steel or cast iron, didn't take much notice of the oil rings...I'll check tomorrow.

 

[SonofJoe]

Originally Posted By: funflyer
Originally Posted By: SonofJoe
Since my last post, I think I have watched that few seconds of the video where he focusses on Piston 4 about twenty times. I now think I was seeing the wrong thing. Silk had it absolutely right earlier in this thread. This is a one piece oil ring! If you look real hard, you can see the tiny drain holes in it. The serrated thing which I thought was an expanded/spacer for two (or one) rails is actually the tensioner spring that sits behind the one piece ring.

FunFlyer, if you're still reading this thread, can you please flesh out what you said about dirt impacting on dwell angle. I'm absolutely positive you have the answer to this mystery. I just want to sure I have this clear in my mind. Please feel free to assume I'm an idiot in these matters!!


Assuming the ring to land clearance is too loose, which it appears to be from the video, the rings will not change direction as fast as the piston, i.e. upstroke changing to downstroke and vise versa. As the piston drives the rings to top dead center, or the uppermost piston travel, the wide gap between the land and ring is at the top of the ring. As the piston starts on the down stroke the gap is now changed to the bottom of the ring as the ring land makes contact with the top of the ring. The exact opposite will happen as the piston reaches bottom dead center.

Now, when everything is new and clean we can assume that the rings and lands are making contact around the entire circumference which means the entire ring will change direction and start to move at the same time and will have little to no stress induced on them, however, when dirt and debris start to fill the excessive gap between the ring and land, the ring in those areas will start to change direction sooner, just in those areas, due to the gap being reduced. Now the entire ring circumference is changing direction at different rates and subsequently causing more stress on the ring and eventually causing failure.

The oil control rings in the OPs engine appear to be either ductile iron or cast iron which we know are not as strong as the old school steel oil control rings so the ring side clearance becomes that much more critical.

As for the repliers that say the ring end gap is too tight, we should have seen an oil consumption problem early in the life of the engine along with severe scoring of the cylinder walls.


Many thanks for this detailed explanation. I think I understand it better now. I used to think I knew a thing or two about piston ring fouling. Clearly I don't!
One thing that did occur to me is if you have an excessive ring side clearance, at TDC and BDC, is there more of a chance for the one piece ring to 'slam' into the top or bottom face of the groove? I could sort of imagine that the extra gap would create a faster relative contact speed between ring and groove face as the the still accelerating ring hits the piston moving in the opposite direction. I know I'm talking factions of an inch for factions of a second but I could imagine the same process repeated over and over might case harden the ring and make it more brittle?

 

[Whimsey]

Originally Posted By: edwardh1
Does toyota have a lot of this problem? something went wrong.
VW in 1979 put bad valve stem seals in many rabbits.
They wold not change the spec until 5 years later when they sued by some US federal regulatory arm, and forced to repair the engines which burned a qt every 200 miles and locked up on freeways, causing wrecks.
German engineering - not responsive


I had a 1977 Rabbit that used oil at a rate of 200 mi to the quart from day one. While under the warranty period VW refused to acknowledge that it was not normal and refused to fix it. VW finally agreed to pay for the new head and I paid the dealer for labor. They only did this because they wanted the old head and I would not give it to them without them supplying the new head. And yes it did cut down substantially on oil usage. I sold the car at 116,000 miles.

Whimsey

 

[SonofJoe]

Originally Posted By: Silk
Originally Posted By: funflyer

The oil control rings in the OPs engine appear to be either ductile iron or cast iron which we know are not as strong as the old school steel oil control rings so the ring side clearance becomes that much more critical.


The cast iron ring is the old school ring, 3 and 4 piece rings replaced them. I've got a BMW V8 apart at work, I was snapping the rings to see if they were steel or cast iron, didn't take much notice of the oil rings...I'll check tomorrow.


Hi Silk,

Sorry for the late reply but the wife's had me working all day!

Many thanks for your input. With what you know, is there any logical reason you can think of why Audi (and from what you say, possibly BMW?) would put a potentially fragile, not particularly efficient, one-piece cast iron oil ring into a modern high performance engine when it looks like the whole world and his dog moved over to steel rail three piece rings years ago? Audi's and Beemers are eye-wateringly expensive so it can't just be because they're the cheaper option (or can it?). The only thing I could think of (albeit a bit conspiracy theory-ish) is that the Audi oil ring grooves were sized for a conventional three piece ring but at the last minute, they switched to the one-piece (possibly because of a supply problem?). It might explain the excessive side clearance and why this problem seems to have caught Audi on the hop.

 

[Jetronic]

cast iron on steel has a lower coefficient of friction, much lower than steel on steel, and I suppose they could use loads of graphite aswell.

 

[SonofJoe]

Originally Posted By: Jetronic
cast iron on steel has a lower coefficient of friction, much lower than steel on steel, and I suppose they could use loads of graphite aswell.


So maybe the decision was driven by a need to get friction down and fuel economy & power up? In which case, why didn't Audi pick up the oil consumption issue in there pre-launch testing and say to themselves, hey if we go ahead with this duff engine, it's going to cost us an arm and a leg in the long term? Thinking about it, if VAG can launch a car with an emissions defeat device, maybe launching a car that munches through motor oil is an easy decision.

 

[Jetronic]

The longer I work in the car industry, the less I'm convinced there's much thorough testing going on. Most of the testing seems to be computer simulations. the stuff that makes it into production sometimes is scandalous. And then we get recalls and TSB's even before the first car makes it to the dealership.

 

[SonofJoe]

That's really interesting...

If it's any consolation, unless things have changed radically since my day, most major passenger car oil go out into the world without any field testing being done. The attitude is very much that if it's passed all the various API & ACEA sequence tests, then the oil is good to go. In fact I might go as far as to say that until the first can of oil gets sold, the oil won't ever have been run in a normal engine, in a normal car on a normal road by a normal driver!

 

[BrocLuno]

Why would they do that? That's what we're here for ...

 

[Silk]

Originally Posted By: Jetronic
cast iron on steel has a lower coefficient of friction, much lower than steel on steel, and I suppose they could use loads of graphite aswell.


I think this is the reason, steel rail oil ring is quite stiff. Over 30 years ago I did a ring job on a 161 Holden engine, should of had it rebored, but the solo mum was stapped for cash. The bore looked like those corugated baked beans tins, and I used 4 piece oil rings in it...and it turned into a nice runner. A few years later and another owner, and it came back to me with a blown headgasket, and the bores were nice and smooth. So pretty agressive.

I've seen those cast iron oil rings with coil spring expander before, but can't remember which engine - too many engines, and too many years.