There are thousands of reported cases online of “spun crank hubs” in stock and modified cars with the S55 engine. The keyed crank hub upgrade is a replacement of your stock crank hub unit with a unit that has four “keys” or “pins” for which 4 holes are drilled into the S55 crankshaft so that upon installation of the crankshaft bolt, the new keyed crank hub can be locked into place permanently without a chance of relative rotation to the crankshaft.

This allows further insurance against the chance of the crank hub “slipping” or “spinning” and un‑syncing the relative angles between the crankshaft and camshafts (this can mean engine failure, which will cost upwards of $20,000 to replace, or at the very least leave you stranded and un‑driveable until the crank hub is replaced and the engine is retimed). This SCH failure has been seen on both modified and stock S55 engines. If you are modifying your car, tracking your car, or even driving spiritedly, then upgrading your crank hub is highly recommended.