So, its been a while, but I have a sad update...
About 2 months ago I took my car in to work. On the drive in in the morning, about 500m from the office, I noticed a noise come on suddenly - a sort of high pitched whining sound that went up and down with the engine revs. It wasn't a belt, but something more mechanical in sound. I pulled in to work and the engine sound rough, so I turned off the engine and started messaging a friend who's pretty hot on these engines. His thought was a belt had slipped or the chain had gone.
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I had to get home at lunch time, I had something important I couldn't miss so I decided to try the car to see if it was drivable. To my surprise, it started easily and there was no weird sounds or anything, so I decided to risk it and drive it home. Weirdly, exiting the driveway at work, the brakes felt solid and were nearly non-responsive. Not good! I took the approach of driving incredibly cautiously and slowly and gave acres of following distance to any cars ahead on the drive.
I made it most of the way home when I was rolling along slowly on a dual carriageway up a hill and the red oil light came on as the engines started feeling really lumpy and rough. I panicked and limped it about a mile up the road into a lay by where I stopped it and turned it all off and made some phone calls.
My friend who I'd been messaging earlier came along and helped me remove the oil filter cover to check if the oil filter had collapsed (something that had happened to a friend's car previously with similar symptoms). The filter was in tact, but full of swarf!
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We replaced the filter with one he had with him, closed everything up, and called a vehicle recovery truck. They dropped the car at a local mechanic for them to look into it and see what they could do.
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Their verdict was the oil pump had failed and the engine was a write-off. They weren't keen to do the investigative work or any rebuilds, so I shifted the car to a mechanic I've used in the past who was keen to take on the work. It sat around for a while while he cleared out a backlog of jobs, and finally he removed the engine.
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He has reported back that the likely scenario that led to this chain of events was the nut that holds the sprocket on the oil pump stripped or sheared off, getting sucked into the engine. Both the sprocket and the nut are MIA.
Current state:
The engine is being stripped to investigate the extent of the damage and make sure the block can be saved and rebuilt.
If it can't be saved, I'm in the difficult position of needing to source a replacement engine. I've looked into it, and they're not easy to find unfortunately. The engine is a N52B30K, which is an upgraded version of what was the original N52B30 in the Z4 series, and features a host of upgrades. I've found older engines with higher mileage, but that's not exactly ideal. I might end up rebuilding a donor engine by stripping it down to the block and replacing all the components with the upgraded parts from the K engine.
Either way, it's eye-wateringly expensive (yet still less than a brand new block from BMW) and a very sad and unlucky thing to have happened!
Watch this space!
