Hey all, thought I would drop some information here about the progress, pretty cool to see so many responses.
After BMW Seattle told me 3700 to take the valve cover off, I called a couple of indy shops which both told me that if they did do the work to diagnose the issue, that if it was engine related they wouldn't work on it. I ended up towing the vehicle home again to see what I could do.
I did a bit of research and discovered that this engine, the n20, has a fatal flaw that impacts customers around 70k-100k miles, where the timing chains slaps against the guide enough that the guide cracks, possibly leading to catastrophic engine failure.
I removed the valve cover in about 3 hours (again, bmw seattle charges 3700 for this) and quickly discovered that the chain guard had broken, a large piece of it is visible in the chain well, though the chain tension still seems ok.
I've separately tested the compression on all of the cylinders and it seems ok (just manually cranking the engine and feeling it compress a good deal), and have also scoped the engine out and did not notice anything obviously shredded in the cylinders.
The plugs were all carbon scorched which I thought was odd, but other than this and the broken guard nothing else looked off to me. I drained the oil and it was clean, and the filter was clean too. I plugged a computer into the ODP port and, besides it being upset about the car being jacked, nothing else was reported as wrong except the valvetronic sensors, which I believe was due to me having it unplugged when I ran the initial ODP scan.
At this point, I've positioned an engine support bar above the n20 and jacked it up about an inch to give me clearance on the underside to remove the pan for deeper inspection. Removing the CV joints was surprisingly easy, which was required first.
My hope is that once I pull the pan, I can visually determine whether or not the engine is possibly salvageable. This would mean reassembling the chain guide to see that none of the parts are missing, and replacing the cog/chain/guide with the updated n20 parts that were released to overcome the fatal flaw in the engine.
If you have an n20 from 2013 or around that time, please be aware that you might be sitting on a ticking timebomb. There was a class action lawsuit for this that has sadly already been settled.
Attached are a few pictures showing what I'm working with, a shot of the broken guide, and shot of me pulling on the center of the chain (I didn't try to find top dead center or anything), and another of the engine being hoisted. Appreciate all the points dropped in this thread so far and any others that folks can provide. I've never worked on engines before so am especially eager to here about gotchas and things to look out for (for example, making sure to mark the joints and drive shaft before removing). Thanks!
