BMW M3 Engine Teardown Shows The Consequences Of Suspected Over-Revving

Engine teardown videos are like a mystery story because you slowly learn more about the cause of the failure as the clips proceed. This particular video, however, is like an Agatha Christie tale because there are so many red herrings. Watch the pieces come off a BMW S55 twin-turbo 3.0-liter inline-six from a 2016 M3, and see how many failures you can spot throughout the video.

Whenever you see a BMW engine with the prefix S, it means that the powerplant comes from the M division. We don’t know whether this 2016 M3 has the Competition package or not, so the mill’s original output is either 425 horsepower or 444 hp.

Gallery: 2016 BMW M3: Review

The exterior of this M3’s engine has some immediate red flags. Portions of the block and oil pan have silver spray paint covering them. There’s a tag from a rebuilder. Worst of all, there’s a waterfall of dried coolant down the back. A melted heat tab indicates the mill overheating at some point. All bad news.

Stripping off pieces doesn’t reveal too many problems, but there’s something odd. The plastic timing chain guides have a 2015 date code, which suggests they’re original to this engine. These aren’t generally pieces you’d keep when rebuilding a motor like this one.

Taking off the cylinder head reveals another surprise. The exhaust valves show contact with all six piston faces. Eric, the channel’s host, doesn’t take apart the head in this video, but he suspects these strikes probably caused the valves to bend. He thinks this damage is from over-revving the engine, as this would explain the uniform markings across the cylinders.

While there’s no definitive explanation for this engine’s failure, Eric has a theory. Since the powerplant has the original chain guides and bearings, he wonders whether this is actually a rebuilt engine. These pieces usually receive replacements if someone performs an extensive service, but they’re still here. So, it’s possible an unscrupulous company sold this mill as a rebuild without actually doing all the work. We hope the owner of this car wasn’t burned too badly on the deal. 

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