Do the rod bearings really need doing, or is that an internet story?
It is real, but the useful version is more precise than the story. The bearing shells in these engines run a tighter clearance than an ordinary engine’s, which is part of how they rev, and that makes them far less forgiving of long oil intervals and high oil temperatures — both of which describe how these cars are used here. What is not true is that every engine needs shells at a fixed distance. The right answer is measurement: an oil sample reports the bearing metals in parts per million, and two samples a few thousand kilometres apart show whether they are rising. That turns the most expensive decision an owner of one of these faces into a planned job or a clean bill of health. We are perfectly willing to tell you the engine is fine and take nothing apart.
My F80 M3 stored a timing correlation fault. Is that the chain?
On most BMWs that code means a chain or a guide. On this engine it usually does not, and mistaking the two is an expensive error. The timing sprocket on the S55 is clamped to the nose of the crankshaft by friction rather than located by a key, and under high load — particularly on a car that has been remapped — that clamp can slip, at which point the engine’s idea of where the crankshaft is no longer matches reality. The code is the same; the cause and the repair are not. So before anything is taken apart we read the freeze-frame data behind the fault and establish whether the car has ever been remapped, because that answer changes the diagnosis. If you are holding a quote for a timing job on an S55, it is worth asking which of the two they have established.
My M5 smokes when I start it in the morning. How bad is that?
If it is a cloud at start-up that clears within a few seconds and then never returns while you drive, that pattern points at valve stem seals — oil draining past a valve while the car sits, burning off in one go. On this engine family that is a known item and a cylinder head job, not an engine. What changes the answer entirely is smoke that carries on under load or that appears when you lift off the throttle, because that points at rings or at the turbochargers instead. Those two look similar to an owner and are nothing alike in cost, so we start the car from cold ourselves rather than work from a description, and run a leak-down test to see whether the cylinders hold pressure. You will get the actual answer before you get a price.
I have been quoted for a new SMG gearbox. Is that likely to be right?
It might be, but it is quoted far more often than it is true, and there is one thing to establish first. SMG is not a gearbox of its own — it is an ordinary manual gearbox and clutch, operated by hydraulics. A pump raises pressure, an accumulator stores it, and the system uses that pressure to select gears and work the clutch. When the accumulator loses its charge the pump runs constantly, selection goes slow, and the car puts a warning on the dash: the exact presentation of a failed gearbox, caused by a part. That should be checked, and the system pressures read, before anyone discusses a gearbox. Ask whoever quoted you whether they measured the pressure.
What should I check before buying an E46 M3?
Two things above everything else, and both need the car on a lift. The first is the rear subframe mounting points in the floor, which can crack on these cars and which nobody can assess from a driveway — the symptom is a clunk from the back, and it is very often sold to owners as worn bushes, so new bushes get fitted into a cracked floor and change nothing. The second is the condition of the rod bearings, which on an S54 is established by oil analysis rather than by listening. Everything else about the car — rust, service history, clutch, cooling system — matters in the ordinary way. Those two decide whether it is a car or a project, and both are exactly what a pre-purchase inspection is for.
