We tune the S55 — the twin-turbo six in the F80 M3, F82/F83 M4, and F87 M2 Competition — and we're going to be straight about it, because this engine has two reputations: a genuine performance weapon, and the one F8x owners lie awake worrying about. Both are earned. Here's the honest version.
What is the BMW S55 engine?
The S55 is M division's 3.0-liter twin-turbocharged inline-six — the engine that powered the F80 M3, F82 and F83 M4, and the F87 M2 Competition. From the factory it makes roughly 425 to 444 horsepower. It's a highly-strung, track-bred motor — tremendously capable, and demanding in proportion.
How reliable is the S55?
Reliable when it's maintained properly — emphasis on properly. This is not a B48 you can be lazy with. The S55 runs hot, works hard, and rewards diligent, thorough maintenance while punishing neglect faster than a softer engine would. Treat it like the performance engine it is and it does well; treat it like an economy car and you find the weak points.
Common S55 problems — including the two everyone asks about
- The crank hub. The infamous one. The factory crank hub is a press-fit, non-pinned design that can slip under high load — throwing off engine timing and, in the worst case, causing serious damage. It's most discussed on tuned, high-boost cars. The fix is well-known: a pinned or upgraded crank hub, which is close to standard practice before chasing big power. Address it and it stops being a worry.
- Rod bearings. The other headline — and worth understanding accurately. Bearing wear is real, more common on pre-2017 cars, but the rods themselves are robust and a bearing failure is rarely a spontaneous defect. It's almost always the downstream result of something else, most often oil starvation. Many owners replace the bearings as preventative maintenance, which is sensible on a hard-used or tuned car.
- High-pressure fuel pump, turbos, overheating, rough idle. The supporting cast — wear items and known issues on a high-output engine that you stay ahead of with maintenance.
We list these openly because pretending they don't exist is how owners get hurt. None of them makes the S55 a bad engine — they make it an engine you build and maintain with your eyes open.
How much power, and is it worth tuning?
Massive potential — the S55 responds hugely to tuning, which is exactly why it's so popular and exactly why the crank hub matters. The more power and boost you ask for, the more the crank hub and oiling become non-negotiable. Done right — pinned crank hub, preventative bearings on a hard car, proper calibration — a tuned S55 is one of the most thrilling builds in the BMW world. When you're ready, build your tune for your car, and our Stage 1 vs Stage 2 vs Stage 3 guide lays out the path. If you want the calmer, more refined successor, that's the S58.
Bottom line
The S55 is a phenomenal, highly-strung M engine with two well-known weak points — the crank hub and rod bearings — both real and both addressable. Maintain it like the performance engine it is, sort the crank hub before you chase big power, and it delivers one of the most rewarding drives BMW has ever built.
Frequently Asked Questions
Is the BMW S55 reliable?
Reliable when maintained diligently — it's a highly-strung M engine, not a low-maintenance daily. The two known weak points are the crank hub and rod bearings, both well-understood and addressable.
What is the S55 crank hub problem?
The factory crank hub is press-fit and non-pinned, and can slip under high load and throw off timing — most often on tuned, high-boost cars. The standard fix is a pinned or upgraded crank hub before pushing serious power.
Do all S55 engines have rod bearing problems?
No — bearing wear is more common pre-2017, and it's usually the result of oil starvation rather than a defective rod. Many owners do preventative bearing replacement on hard-used or tuned cars.
Which cars have the S55?
The F80 M3, F82/F83 M4, and F87 M2 Competition.
Is the S55 worth tuning?
Yes — it responds enormously. Just sort the crank hub and oiling first, because the things that make it fast are the things that make those parts matter.