BMW crankhub and timing: the six-cylinder turbo field guide

Five engines, two crankhub designs, one chain-drive redesign, and a pile of torque-plus-angle fasteners that all share a rule: the bolt you took out does not go back in. This is the map. Each engine has its own page with the full tables; this one is the "which car, what is it, what's the job" layer.

Which engine, which design

The one table that matters most

Central fastener at the nose of the crank, per engine, straight from the ISTA torque documents:

What fails, per the factory — and what doesn't get claimed

The honest core of this whole subject: ISTA documents design and renewal law, not failure statistics. There is no mileage table for crankhub slip, no wear limit for grip discs, no chain-stretch service interval in this data — and we won't print one. What the documents do establish:

• **N54:** the friction plates between the friction surfaces are mandatory and damage-critical — "the engine will incur damage if the friction plates are damaged or are not fitted." That's the factory's own crankhub statement.
• **N55:** the chain procedure split at **March 2012** production — different tensioner handling, an added oil-pump chain tensioner sealing-cap step. A build date, not a folklore mileage, decides your procedure.
• **S55:** the strictest renewal list in the family — after each central-bolt release, the bolt, the Eka grip disc, and both camshaft sprockets (grip discs welded on) are renewed "without fail." Breakaway torque on the central bolt exceeds 600 Nm.
• **B58/B58TU:** the TU's one-piece chain drive (no intermediate shaft, no second chain, 8 mm sleeve-type chains, 23/46-tooth counts) is the factory's documented redesign of the timing drive — the closest thing to an official "we changed it" in the whole corpus.
• **S58:** belt drive adapted around the damper (extra tensioning pulley), chain housing and VANOS mounts are S58-specific; repair data reaches it through B58TU-validity documents.

What the job looks like, honestly

• **Damper-only R&R** is accessible on every engine here. N55's document is the one that says it out loud: do not release the central bolt; if you do, the timing gets readjusted.
• **Chain tensioner replacement** is a real, small job on N54/N55/S55 (55 Nm, new ring, drain the chamber on reuse) and on B58/S58 (20 Nm + 40°, new sleeve).
• **Timing chain replacement** on N54/N55/S55 is an in-car, front-of-engine job with the crank locked at TDC and the camshafts pinned. On B58/S58 the factory document is engine-out on the assembly stand — that's not us being cautious, that's the procedure as written.
• **S55 hub replacement** is engine-out, full stop.

Costs

Here the data runs out and so do we, deliberately: ISTA carries no parts pricing or book-time rates, and repair costs move with platform, shop, and parts source. What we can say from the documents: the renewal lists above are the parts lists. An S55 hub job isn't one bolt — it's bolt, grip disc, and both sprockets. Budget from the factory's own mandatory-parts language, not from a forum's "while you're in there."

Where to go next

Each engine page carries the full torque tables (crankhub, chain drive, VANOS), the special-tool lists, and the honest step summaries:

• N54 — the original friction-plate crankhub
• N55 — the March 2012 split and the aluminium VANOS screws
• S55 — the grip-disc law and the 600 Nm bolt
• B58 — no hub, TTY damper bolts, and the TU chain redesign
• S58 — B58TU architecture, coverage stated exactly as the data provides it

Every number on every page in this series traces to an ISTA document id listed in that page's sources. If a number isn't there, we didn't print it.