This particular engine came to us with a rap or clatter. That often signals a timing chain problem, but it can point to other things, like bearing failure. We started by draining the engine oil, where we found some troubling evidence:
The bits you see in the photo came out with the oil, and are shown with my finger for size perspective.
Looking closely at the debris in the oil we noted a couple things. Most of the chips are aluminum or plastic. None are bearing metal. There is no sign of the bearing substrate either. It is a distinctive coppery color. But there was no question the engine had to come out of the car, and come apart. We could not assemble it without ensuring all the debris had been cleaned and any damage found and fixed.
The timing chain and gears looked good for 80,000 miles, though they are ready for replacement. We have seen these with the gear teeth worn to nubs and we've see chains strutted so much they won't sit tight on the gear anymore. We've also pulled front covers and found the engine so full of sludge that the motor needed complete overhaul. This motor didn't have any of those problems. But Daniel Ferrari, the tech working on this car, spotted something unusual when handing the timing chain and gears. The balance shafts did not turn smoothly. When he pulled them out this is what he found:
The shafts and bearings were badly torn up. Clearly they had run out of oil at high rpm, and the strong steady pull of the timing chain was all that kept them going, enough that they melted the housings. What could cause a loss of oil?
The balance shafts are supplied with oil through holes in the housing. The holes contain plastic rings and screens, as shown. Those screens had come apart, meaning they ingested sediment that then push through from the system oil pressure. That's more evidence of high rpm failure.
Examination of the bearings and crank showed only light scoring. The inside of the sump was largely free of sludge.
The rest of the engine appeared free of damage, but the debris from the balance shafts made a fully teardown and cleaning essential. We don't know what blocked the tiny balance shaft screens. It may be they are designed wrong, and the screen was too small, so it got pushed into the bearing area. Or the oil may have broken down at some point, and chunks of sludge started the failure. We may never get an answer. Problems like these are really becoming ubiquitous on these high performance, long service interval Euro engines. In the photo below Danny is replacing the very same pieces - balance shafts and gears and chains - on a Mercedes E350 engine of the same vintage:
Here are photos of the old and new balance shaft gears. See if you can identify the wear that constitutes failure:
If you hear noises inside one of these newer engines you can expect a repair cost in the $5k+ price range, in most parts of the country. I've heard reports of these jobs running $15k in big city dealerships with high labor costs.
The moral of the story (in my opinion, car makers don't always agree) is: Change your oil a bit more often than specified. Never deviate from the manufacturer spec for oil. Don't use oil that says "recommended for." Use oil that says "approved for." And when buying a used car, walk away from any ex-lease car that had the oil done at 20,000 mile intervals. You'd be shocked how common that is.
John Elder Robison
John Robison is the founder of J E Robison Service Co of Springfield, MA. His company specializes in the repair and restoration of Audi, Porsche, BMW, Mercedes, Land Rover, Rolls Royce and Bentley motorcars. John is also known as an author and advocate for people with autism and neurological differences. His books include Look Me in the Eye, Be Different,and Raising Cubby. John has also written numerous articles on European car service and repair, and he’s a frequent contributor to the RROC technical forums. He’s always available to advise owners about the care and feeding of their fine motorcars. www.robisonservice.com 413-785-1665
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