Valve cover and gasket: the N54/N55 oil leak job, breather membrane included

Oil smell at the back of the engine, a slick on the trans tunnel, and spark-plug wells full of brown — that is the N54/N55 valve cover gasket announcing itself. The cover is more than a lid: it carries the crankcase-breather system inside it, which is why this leak always gets diagnosed alongside a rough idle. Here is the factory procedure, the torque numbers our ISTA extract can prove, and the one torque it cannot.

What the factory job looks like (N54)

The procedure is 11 12 000. Its preliminary list is the real time budget: battery negative off, rod-type ignition coils out, injector wiring unclipped, and — on the N54 document — injectors out and the right tension strut removed to make room. The vacuum lines to the brake servo unclip and move aside before a single cover bolt turns.

Two installation notes from the factory document are the difference between a fix and a comeback:

• **The slotted sleeves that guide the ignition coils must be replaced** when the cover comes off — they are a wear item in this procedure, not hardware you inspect and reuse.
• **The gasket presses into the cover**, not onto the head — fit it into the cover's groove before the cover goes anywhere near the engine, and replace it, always.

The N54 document releases the cover screws with special tool 11 8 620 (the deep socket for the recessed fasteners) and points the cover screws' torque to the 11 12 4AZ table — see the honest-gap note below.

Torque specs — what we can prove, and the one we cannot

The breather membrane: why this job fixes rough idles

The cover is the top half of the crankcase ventilation system — the breather membrane lives under it, and the N54/N55 cover with a torn membrane mimics half the fault codes in the book: rough idle, lean trims, oil in the intake, whistling oil cap test. The factory data covers the plumbing around it (11 12 030 for the ventilation line; the vent connection and its sealing ring in the torque table above), but the membrane itself is not a serviceable part in ISTA — it is part of the cover assembly, which is the factory's quiet way of saying the fix is a cover.

The honest diagnosis sequence when the cover is off anyway:

1. 01Check the gasket groove and sealing faces for the actual leak path — old rubber goes hard and takes a set.
2. 02Inspect the ventilation connection and its sealing ring — it is a listed replace-item in the torque table.
3. 03If the symptoms were breathing-related rather than oil-related, the membrane is the prime suspect — and it ships inside the new cover.

B58: same job, different fastener discipline

On the B58 the cover bolt pattern uses two-stage torquing (8 Nm, then 11 Nm) — a mini TTY ritual on M6 fasteners. The procedure document also runs through the coil-cover and wiring preliminary work in G-chassis order. The failure folklore is quieter here — younger fleet, better elastomers — but the job logic is identical: new gasket seated in the cover, new sealing rings on every disturbed connection, torque in stages.

Coverage notes

What the data carries: full R&R procedures for N54 and the multi-engine families, the sleeve-replacement and gasket-into-cover notes, N55 and B58 cover torques with per-row engine validity verified, and the attachment torques (non-return valve, vent connection, filler neck). What it does not carry: the N54 cover-screw torque in any table our extract includes, a membrane test procedure, or a mileage-when-it-leaks number. Any "they all leak by X miles" claim is folklore — treat the leak path and the elastomer's condition as the evidence.

Every number above traces to the ISTA document ids in the sources; the one number we could not trace is flagged as such instead of invented.

FAQ

• **Do I need the special socket for the N54 cover screws?** The factory document releases them with tool `11 8 620`. A quality thin-wall equivalent works — the fasteners are recessed more than they are exotic.
• **Gasket alone, or cover?** Oil leak with intact breather behavior: gasket. Breathing symptoms (rough idle, lean codes, oil cap vacuum test gone weird): the membrane rides in the cover — that is the factory parts logic.
• **Why does my new gasket leak again?** The two factory answers: gasket not pressed fully into the cover's groove, or slotted sleeves reused. The third is over-torque on a cover the extract cannot give you an N54 number for — which is exactly why you look it up.
• **Does the walnut-blasting job need the cover off?** The N54 walnut procedure lists the cover as preliminary work — if both jobs are due, one teardown covers both. See our walnut guide.