Owners ask for a B58 when they have an N55, and the other way around, because both are turbo straight sixes and the power figures overlap. The blocks, the sumps, the turbos and the engine computers do not overlap. The engine in the car is the one you replace, unless a specialist is building a full conversion with a stand-alone loom. We sell the engine that matches the VIN.
They do not swap
The N55 is the single-turbo six in the F30 335i, F22 M235i, E90 late 335i and similar cars. The B58 is the modular six in the G20 M340i, G30 540i, G05 X5 40i and the later 440i. A B58 will not bolt to an N55 gearbox and loom. Budget for the engine your chassis was built with.
Checking a used N55
On an N55, ask about the valve cover and the oil filter housing. Both weep, and a housing leak drips onto the belt. The electric water pump and the charge pipe are wear parts you can transfer or renew at fitting. The turbo wastegate rattle on early N55s is worth a note if the engine can still be heard. On a pallet engine, the photos of the turbo housing and the oil pan tell you more than a sales line.
Checking a used B58
A B58 should be bought by the full code: B58B30A, B58B30B, B58B30M1 or B58B30C are not the same tune, and the oil pan changes with xDrive and with the chassis. Check the high-pressure fuel pump area and the coolant pipes for staining. Direct injection means the intake valves will have some carbon. That is normal. Heavy oil smoke on a running engine, or metal in the oil, is not.
Mileage on its own is a weak filter. A 140,000 km B58 with a clean service record and the right pan is a better buy than a low-mile engine of the wrong code.
Do not mix the loom
The engine computer, the injectors and the turbo actuator are a set. An N55 loom on a B58, or a B58 pump on an N55 rail, will crank and then refuse to run, and the fault codes will look like a bad engine. Label every connector you move, and keep the wiring that came with the engine you bought if the car's loom is damaged.
Use new coolant and bleed the electric pump properly. An air lock on these sixes overheats one bank or the head and the engine is blamed for a hose.
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.