[RobotHamster]

2014 220i N20B20U0 Engine with Stage 1 Map to ~250 with air intake and exhaust modded.

My first mistake was buying a car that was already mapped and modded. Had it for 6 weeks, no issues, then it all went haywire.

I'm getting a misfire in cylinder #2.

Garage said they did a compression test getting 0psi on #2, plus a leakdown test claiming that

"Inlet and exhaust valves sealed, but large escape of air from oil filler cap/dipstick."

Then

"Carry out bore inspection with camera and found cylinder wall in very poor condition in cylinder 2, with large section of bore showing signs of scoring. Suspected broken piston ring land. Requires engine removal and full strip down to confirm."

Ultimately they've said it's needing either a new (remanufactured) block and pistons from BMW or a new (remanufactured) engine from BMW.

The block and pistons quote comes with a new timing chain, new gasket seals, new crankshaft and conrod bearings, plus labour and their effort to return it to a stock map coming out at around £6700.

New engine isn't worth thinking about imo (13K)

Quotes and investigation was done by a "German Car Specialist" who only use BMW supplied parts.

I've been quoted anywhere from 1500 to 5000 for a for a 2nd hand or reconditioned engine plus fitting.

I eventually got my own camera, and the bore mostly looks clean, nice cross hatch pattern is visible all round, with a darker ring up top that I've been told is about TDC for Cylinder 2.

Its in this ring that scoring is visible, in the attached picture (oriented and cropped to have the valves up top)

I'll try and get a better picture after work, and the current error codes, because I've lost my obd2 screenshot.

Please correct me if I'm wrong, but this doesn't seem to me to be a piston ring, or main cylinder bore issue.

Current suggestions, beyond the engine being completely shagged by a bad remap/bad injector/bad fuel, are either a VANOS or Valvetronic issue.

The area of timing chain which you can check through the oil filler cap is tight and not , but could potentially have jumped a link elsewhere - but if it were general timing issues, I'd expect issues in more than just a single cylinder.

I've got a mate than can start taking the engine apart in a couple of weeks to properly diagnose things, but I'm just wondering if I should cut my losses and try to sneak it through a webuyanycar trade in.

[Coupsoup]

If your chain skipped a tooth you'd 100% have a timing code.

The n20 is notoriously bad if the timing and oiling aren't meticulously taken care of. I'd highly recommend against a used unit.

They likely wont warranty any repair as long as you have a tune, especially if they're thinking the increased boost (and cylinder pressure) is the cause of the ring breaking.

Honestly, as a professional technician, it sounds like they've done a good job on the diagnosis and they have high standards for their repairs.

If you can afford it I'd let them take care of it.

You've been lucky the damage is above the piston rings so far, make sure you park that car.