Failure mode - 6.6L V8 Gasoline (GM HD, L8T 2020+)

Valvetrain hardware failures: lifters, valves (no AFM - attribution guard)

Reliability tier: aggregated - verify before ordering, see /disclosure/

Symptoms

persistent ticking, misfire on one cylinder, low compression on a bore (lifter/valve hardware)
owner reports of dropped/broken valves and lifter replacements (GM-Trucks HD forum); some early-engine 'improperly torqued cylinder head' anecdotes

Compare with the other causes of the same sign on this engine: ticking, knocking, rattle or whine · misfire, rough idle, hesitation or surging (4 causes)

Root cause

The L8T has NO AFM/DFM cylinder deactivation - it runs the full V8 at all times - so the famous Gen V 'AFM lifter collapse' pattern of the light-duty 5.3/6.2 does not mechanically apply. Valvetrain hardware failures reported on HD forums are therefore standard hydraulic-lifter/valve-spring/valve failures (or misattributed LD experience), and no root-cause pattern is settled in the open record.

Diagnosis

cylinder-contribution test and compression/leak-down to separate lifter, valve and injector causes (DI misfires overlap)
inspect the valvetrain via valve cover before ordering heads or long blocks

Fixes

replace failed lifter/valve hardware; cylinder head service or replacement where a valve dropped ()

Prevalence

occasional