The S55 is the twin-turbo six in the F80 M3, F82 M4 and F87 M2 Competition. A used one is expensive because the cars are, and because a short block failure is a workshop job measured in days. Buying the wrong ancillaries, or an engine with a known bearing noise, wastes that money twice.
What the S55 is
It is not a tuned N55. The block, the crank, the turbos and the sump are S55 parts. An M2 Competition, an M3 and an M4 share the family, but the oil pan and the engine mounts still have to match the car on the ramp. S55B30 and S55B30A both appear on listings. Match the full code to the VIN.
Bearings and the hub
Ask two plain questions. Have the rod bearings been inspected or replaced, and has the crank hub bolt been upgraded? Early S55 engines had a crank hub bolt that could loosen. Bearing wear shows up as a knock once the engine is hot and under load, which you cannot hear on a pallet. If there is no history, say so in the order and budget a bearing inspection when the sump is off for fitting. That is cheaper than finding out after the first track day.
Turbos and the sump
The two turbos should spin freely and the housings should be dry. Oil pooled in a compressor housing is a reason to ask for another photo before you pay. The sump on these cars is shaped around the front axle. An engine from a different chassis can be the right block and the wrong pan.
We photograph the stamp and the pan in Hamburg. If you want the bearing history and there is none, we will tell you that too.
Full S55 guide · S55B30A from an F80 M3
The first hours
Fill with the oil grade specified for the S55, not a generic 5W-30 from the diesel bay. The cooling system on the F80 and F82 needs a proper vacuum fill. A low coolant level on this engine is not a small top-up. It is how heads get cooked.
If the bearings were not documented, the sensible time to inspect them is before the car is handed back, with the sump already accessible. A road test that includes one hard pull is enough to hear a knock. It is not a substitute for looking.
The yard is at Andreas Meyer Straße 38, 22113 Hamburg. Call or WhatsApp +49 15510 030835, or email autowerkeengines@gmail.com, Monday to Friday, 9:00 to 16:00 CET. Shipping is 249 € per order. We are an independent seller, not BMW AG.