EnginesN54 N55 S55 B58

Head gasket and TTY head bolts: stage tables, the retorque answer, machining limits

Factory head-bolt torque stages for N54 and B58 (both bolt grades), the torque-to-yield law, the retorque question answered honestly, and the machining and flatness limits for these heads.

5 min readUpdated 2026-10-19Rapid Racing

The head gasket job looks like a cleaning exercise with a torque wrench at the end. It is — except the torque tables have four stages, the bolts are one-time-use, and the factory flatness numbers decide whether the head goes back on or goes to the machine shop. Here is the complete data set for the N54 and B58, plus the answer to the question everyone asks.

The TTY law

Torque-to-yield bolts are stretched deliberately past their elastic limit when installed. The angle stages after the torque stage are not extra clamping you can skip — they are the stretch that makes the bolt behave like a spring at exactly the clamp load the gasket needs. Three consequences:

**One use.** A bolt that has been stretched to yield will not return to its original length when removed. Reused, it stretches further at lower clamp load, or snaps. The factory marks every head bolt "renew" on all four platforms.
**No retorque.** Ever. There is no factory retorque stage in any of these procedures, and a TTY joint cannot be usefully retorqued — the bolt is already at yield. If the gasket weeps, the fix is a new gasket done right, not a wrench on stretched bolts. This is the honest answer to the forum's favorite question.
**Clean, dry-ish holes.** The N54 doc's warning is explicit: no fluids or contaminants in the head-bolt threaded holes. Oil in the hole hydrolocks under the angle stage — the bolt reads "torqued" while the joint is loose, or the block cracks. If a bolt bottomed on oil, stop.

N54 head bolt stages

The N54 head uses mixed bolts — M11 in the high-load positions, M9 elsewhere — all replaced on assembly.

Fastener	Thread	Spec	Torque
Cylinder head bolt	M11 x 135	Renew	30 Nm + 90° + 90° + 45°
Cylinder head bolt	M9 x 95 / M9 x 125	Renew	30 Nm + 90° + 90° (omitted per factory table for these lengths) + 45°
Cylinder head bolt	M9 x 30 / M9 x 70	—	22 Nm
Cylinder head cover to head	M6	Tighten crosswise, inside to outside	8.5 Nm

ISTA · factory documentN54 cylinder head bolts — factory torque stagesOpens in your account's service knowledge — sign-in required.

B58 head bolt stages

The B58 went to a uniform M11 pattern — 14 bolts — with two bolt grades that torque differently. The grade is identified by screw head height.

Fastener	Thread	Spec	Torque
Head bolt, grade 13.9 (head height 13 mm)	M11 x 1.5 x 188	Renew	30 Nm + 50 Nm + 90° + 90° + 90° + 90°
Head bolt, grade 11.9 (head height 11 mm)	M11 x 1.5 x 188	Renew	30 Nm + 90° + 90° + 90°
Head bolt to timing case cover	M8 x 40	Renew	19 Nm

ISTA · factory documentB58 head bolt stages by grade — factory procedureOpens in your account's service knowledge — sign-in required.

The factory procedure has you feed all 14 bolts in the numbered sequence, mark each bolt head with a line after the jointing torque (before the angles), then run the angle stages — the paint line makes the angle visually verifiable. Bolts 1–5 by the timing case cover get their own M8x40 renew-and-19-Nm note.

The gasket laws (N54)

The factory replacement procedure (11 12 101) is short and strict:

The N54 gasket is a beaded metal gasket with rubber coating — check the identification mark on the new gasket against the engine before it goes on.
Adapter sleeves in the block must be checked for damage and firm seating.
Work the sealing surfaces with the special tool (11 4 470) only — no metal-cutting tools, no Scotch-Brite on a drill, no "just scuff it with sandpaper."
Before the head goes back: check the head for flatness and pressure-test it (our block-off guide covers the factory watertightness procedure).

ISTA · factory documentN54 head gasket replacement — factory sealing lawsOpens in your account's service knowledge — sign-in required.

Machining and flatness: the go/no-go numbers

Measurement	Factory value
Head height, new	112.00 ± 0.05 mm
Machining limit (minimum height)	111.70 ± 0.05 mm
Max material removal in one resurfacing	0.3 mm
Flatness deviation, longitudinal	0.10 mm
Flatness deviation, transverse	0.05 mm

The height and machining-limit numbers are identical across N54, N55 and S55 — the heads share the dimension book. The flatness numbers come from the N54 milling procedure: straightedge on the sealing face, feeler checks both directions. Past the limits, the head gets milled (0.3 mm max, to the 111.70 limit) or replaced — a milled head changes the effective squish and, on these engines, eats into the head gasket's designed crush zone.

ISTA · factory documentN54 head milling — flatness limits and 0.3 mm maximumOpens in your account's service knowledge — sign-in required.

Proving the job: compression

After the head is back on and the engine has run and cooled once, the factory compression spec is the pass/fail: N54 builds 14–16 bar with a maximum cylinder-to-cylinder deviation of 2 bar. Low or uneven numbers mean the joint or the valvetrain under it needs attention — not another pass with the torque wrench.

ISTA · factory documentN54 compression pressures — factory acceptance valuesOpens in your account's service knowledge — sign-in required.

Sequencing with the rest of the rebuild

The head gasket job shares disassembly with the timing refresh — chain, tensioner, VANOS all come off the front. Do the valvetrain guide's checks while the cover is off, torque the chain components per the crankhub guides, and prime the oil system before the first start.

Factory sources · ISTA