The Mysterious BMW N52 Engine Failure

This story doesn’t really have a point—just thought it was interesting and weird. Never seen anything like it and can’t explain it.

I purchased a scrap LCI E83 a few weeks ago and finally got around to tearing into it. Being an N52 with no compression, I figured it was likely VANOS-related. The engine isn’t known for piston ring issues, so I was hopeful.

The engine had the VANOS recall completed about 6 months prior, so I didn’t know what to think. I’ve seen VANOS bolts fail after they were supposedly replaced in the past, so I thought that was a possibility, though unlikely given the recency.

The previous owner brought it in for a no-start condition. I got the paperwork from them and it had some notations about the work done:

I got my borescope and checked the intake cam—all bolts were intact. Unable to see the exhaust cam due to the valve cover design, I had to pull it off. To my surprise, all exhaust cam bolts were intact as well. But yeah, there was a broken head bolt. Wild.

At this point I didn’t know what to think. When scanning codes earlier, I noticed the temp gauge was pegged high even with the engine off (just ignition power). The previous owner mentioned it was overheating before it died.

Now I’m thinking the head was ridiculously warped — further supported by the fact that the head bolt broke — and that the head gasket had somehow blown across all cylinders. Far-fetched, I know, but I don’t have any other explanation.

I tested compression once more for my own sanity—still 0-20 PSI across the board.

Now I’m invested. I don’t care about fixing it; I just want to know what happened. So I pulled the head (not easy, by the way). The broken bolt being a stud meant I had to bring the head straight up. The configuration of the engine bay makes it impossible to pull the exhaust manifold back enough to clear the head without being able to move the head itself. Yeah, not fun. The engine wasn’t designed for this car, so most of its setup was an afterthought.

The head came off. The gasket was intact. No signs of failure.

Beyond confused, I called it a night—it was dark out and I was tired.

There was easily a millimeter-thick coating of carbon on all surfaces, including the seat.

Honestly, I can’t explain how that even happens. It doesn’t matter the amount of carbon or oil accumulating—that seat should always be shiny. The force of the valves opening and closing should keep it clean.

I’ll include pictures of the valves below. For reference, I’ve also included a valve from my N55 that has tons more buildup but still maintains a shiny ring where it should.

This remains one of the most bizarre engine failures I’ve encountered. The complete loss of compression across all cylinders with an intact head gasket and no visible damage is perplexing enough, but the carbon buildup on the valve seats defies explanation.

Here’s a few other pictures from the teardown process. I didn’t take many. The photos tell the story of one of the most unusual failures I’ve come across.

Still can’t explain it. If you’ve seen anything like this before or have theories about how carbon can accumulate to this extent around the valve seats — to the point of zero compression — I’d love to hear from you.