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In this forum chat, we’re talking about a post I’ve seen from Facebook which asks, why does the V12 engine always seem to blow up the cylinders and 11 and 12.
Very easy answer for this. That particular type of failure where it’s 11 and 12. It’s normally 12 and 6. These are the rear cylinders, the last two share a big end crankshaft journal. And this type of failure normally arises from the oil level dropping low, normally because the breather circuit is failed and the engine is consuming its own oil to the point where it drops so low that the oil system struggles to get enough oil. It’s pretty much the last journal in the circuit which is the rear of the crankshaft, which is spinning some of the 6 on the 12, and then okay, so there are 11. It’s still at the back but a different journal of one from the rear.
Due to a lack of oil flow, oil feed to the big M bearing fails and then there’s quite a clearance between the con rod and the crankshaft. That movement causes the rod to fail, causes the piston to become detached and normally bury itself in the cylinder head. So, when you take the engine apart, all you see is a few cylinders normally 6 and 12, could be 11, with failed pistons.
And someone might not be able to piece together all the bits of information to realize that failure occurred due to oil starvation and it was a bearing stroke, rod breakup. Very rarely, even DB9 from 450 horsepower up to 510 derivative engines do not detonate. No matter how much you advance the spark on those particular engines there’s no detonation. So, it’s not going to be a top end failure, it’s not going to be overpressure above the piston, cracked rings, cracked land and a piston combustion related failure. Liners, these never crack, never drop. So, any chats detached piston, any failure of the combustion chamber is normally a big M bearing and connecting rod associated due to low oil flow.