M Power servicing and performance

What is different about servicing an M car?

Almost all of it. The engine, cooling system, brakes, dampers and driveline on an M car are different components from the standard model's, they sit on their own service intervals, and the electronics around them are calibrated to expect exactly those parts.

Fitting the standard-model equivalent because it physically fits is where the expensive problems start, and they are usually discovered later, by somebody else, after the symptom has become something larger. An M car serviced to a standard schedule with standard parts is not a serviced M car.

What should be checked before a track day?

Track use compresses a service interval into a weekend. The things that cope on the road are the things that stop coping first under sustained load, which is why a pre-track inspection concentrates on heat, fluid and friction rather than on a general once-over:

• Brake fluid condition, because fluid that has absorbed moisture boils, and boiled fluid gives you a long pedal at the end of a straight
• Pad and disc material and thickness, with the honest conversation about whether road pads are the right choice for what you are about to do
• Cooling system condition and coolant level, which is the system most likely to be the limiting factor on a hot day
• Oil level and condition, checked for the way the car is about to be used rather than the way it has been
• Tyres, including age and condition rather than just tread depth
• Suspension and bushes, and anything with play in it that will get worse quickly

Afterwards is worth a look too. A car that has done a track day has had a harder life than the mileage suggests.

Can you do performance work, and should I?

We do software and hardware work, and we specify it around what the rest of the car can take. More power asks more of the clutch, the cooling system, the brakes and the driveline, and an upgrade that outruns those turns a fast car into an unreliable one.

So the conversation starts with what the car is for. A car that does occasional track days needs different decisions from one that is a daily drive, and the right answer is sometimes to spend the money on brakes and cooling rather than on power. If the car does not need the work, we will say so.

What can you do about a noisy valve train?

We carry out exhaust cam alignment, which is the usual answer when an M engine develops a noisy valve train. It is a measurement and correction job rather than a parts job, and it is the kind of noise that gets quoted as a top end rebuild by somebody who has not checked the timing first.

We also do crank hub upgrades. The standard hub holds its position by clamping force rather than by a key, and on an engine making more than it left the factory with it can move, which throws the timing out and takes the engine with it. An upgraded hub pins it mechanically. If the car is tuned, or you are about to tune it, this is the job that comes first.

What goes wrong on each M engine?

Each M engine has its own known weak points, and working out which one applies to the car in front of you is most of the diagnosis. The list below is what these engines are actually known for, rather than what a generic fault code reader will tell you.

S55 — F80 M3, F82 and F83 M4, F87 M2 Competition

The crank hub is the one everybody has heard of. The hub holds its position by clamping force rather than by a key, and it can move, which shifts the crank timing and can put pistons into valves. It gives no warning before it happens, and it shows up far more often on cars making more than standard power. The fix is a capture plate or a keyed hub, and it is cheap next to an engine.

Less dramatic and far more common: the factory charge pipeis plastic and splits or blows off under boost, thecharge cooler is a known failure, and oil leaks from the valve cover, sump and filter housing turn up at higher mileages. Rod bearing clearances on the S55 are argued about; opinions differ and we will tell you what we actually find rather than what the internet says.

S63 — F10 M5, M6, X5 M and X6 M

The valve stem seals are the classic one. The hot-V layout puts the turbos between the cylinder banks, the seals harden in that heat, and oil gets past them into the combustion chamber. You see it as blue smoke on a cold start or on the overrun, and as oil disappearing between services. It is a heavy job because of how tightly the engine is packaged, which is exactly why it gets quoted as something else.

Rod bearings are the other watch item, and preventive replacement is widely done in the M world rather than waiting for a noise. Copper in the oil is often the only sign before a knock. Turbo oil seals, ignition coils and the cooling system are the rest of the list.

S58 — G80 M3, G82 M4, X3 M and X4 M

The S58 has no single catastrophic flaw, and that is the honest summary. What it does have is carbon build-up on the intake valves, because it is direct injected and no fuel ever washes over the back of the valve. It arrives as a gradual loss of throttle response, a rough idle or misfires, and it is cleaned by walnut blasting. Cars doing short trips build it up faster.

Beyond that it is cooling system plastics ageing faster than they would on a standard car, and the occasional fault that turns out to be software or a sensor rather than anything mechanical. Worth knowing before somebody sells you a repair.

S65 — E90, E92 and E93 M3

Rod bearings. The S65 runs tight tolerances on relatively small bearings, and preventive replacement is treated as routine maintenance on these cars rather than as a repair. It is done on condition and history, not on a date.

The other one is the throttle actuators, one per bank. The gears inside are plastic, they wear, and the car drops into limp mode with the revs capped. It reads like something far worse than it is.

There is nothing on that list we have not done. Most of it we did inside BMW, and the hard ones are the reason other technicians used to bring us theirs. If your car is doing one of these things, tell us what it is doing and when: half of this is identifiable before the car is on the ramp.

Why bring an M car to an independent?

Because the people working on it trained on these cars inside BMW, and because we read them on BMW's own system rather than a generic tool. The things an M owner tends to want, which are someone who knows the model, the right parts rather than the nearest ones, and a straight answer about what is actually needed, are not things that require a main dealer's price list.

We are at Unit B2, Fram Enterprise Centre, Heol-Y-Sarn, Edwards Business Parc, CF72 8QZ, within reach of Cardiff, Bridgend, Pontypridd, Talbot Green and Llantrisant.