E60: Engine Autopsy Verdict.

Well, contrary to my earlier verdict of no damage to the head, a bit of informed explanation reveals the corroded surfaces in cyl. 6 are in fact battered metal from the where bits of my swirl flap were bouncing around inside it. Not good!

After having my photos pored over by the engine diagnosis experts on BMW Land, the best version of events of that fateful Tuesday are below:

1. Swirl flap no. 4 breaks up and bits enter cyl. 4.

2. Inlet valves jamming open on cyl. 4 cause a backfire and blasts the loose remains of the swirl flap into the intake plenum.

3. The turbo forces the swirl flap remains along the plenum, with bits ending up in cyl. 5 and the majority entering cyl. 6.

4. Cylinders 4 and 5 continue to fire with slight lack of compression.

5. Trapped debris in cyl. 6 begins to ricochet around, causing damage to the alloy piston-crown and the top of the combustion-chamber in the head until the inlet valves cannot close fully and compression is lost entirely.

Worst bits:

• Cylinder-head is finished. Valve-ports on cyl. 4, 5 and 6 need regrinding and fitting with some new valves. The top of the combustion chamber in cyl. 6 needs completely regrinding into shape.

Best bit:

• The engine still turns freely, cyl. 4 and 5 are virtually damage free and do not need replacing.
• Piston 6 compresses in the block still, so no damage to piston-rings.
• There is no damage or scoring to the cylinder walls.

THE REPAIR [in theory...]

• Repairing the head will cost ~£350, the cheapest Birkenhead-Engines can do and may still need further work, so a replacement is needed. Birkenhead-Engines say they have one such in stock, removed from another E60 530d, though what year they are unsure. It is not re-con and they say I can take my chances for a mere £200, but at least they know the valves etc. all work so it looks like this is the way to go.
• As long as I remove any tiny debris from cyls. 4 and 5, I am happy that they are working 99% as well as they should and do not need any repair.
• Cyl. 6 is battered and, although it is compressing in the block, the jagged metal crown will mess up proper combustion even if it fires ok. Worse, bits of the jagged alloy will probably break off during combustion and ping around the cylinder some more, potentially messing up the valves again so really the piston needs replacing.
• Not only is finding a single replacement piston very difficult, the job to replace it requires removal of the sump and big-end shell. This, with all the under-trays and cross-members is a colossal task in itself and, with the car parked on loose gravel, it's looking like a no-go.
• The short-cut solution to piston-6 looks like it's going to be a jenky regrind with the piston still in the engine. I will turn the crank by hand so that piston-6 is in its topmost position and get in there with a die-grinder, removing all the proud bits of metal and re-shaping the 'swirl-pot' and piston-crown as well can be. This ultimate bodge could be the end of a relatively unscathed engine. It could also be the only way to get the E60 back on the road quickly and with a minimum of fuss... Fingers crossed.

COST:

• Replacement cylinder-head: £225. [Birkenhead Engines]
• New head-gasket: £85.55. [Euro Car Parts]
• New head-bolts: £37.48. [eBay: dusty789blue]
• Swirl-Flap Blanking Plates: £20.99. [eBay: myldanautodesignltd]
• New thermostat: £33.99. [I broke the housing - Ebay: carpartssaver]
• Oil: £85.98. [Halfords, own-brand BMW Fully Syn. 5w30]
• Coolant: £22.99. [Halfords, Comma G48]

TOTAL: £511.98.