Overhead Set After Head Reseal on a High-Mileage ISX
A 2013 15L engine with 780,000 miles comes in for a leaking head gasket. The shop resurfaces nothing (head is within flatness spec), installs a new gasket, and the tech performs an overhead set with a torque wrench and dial indicator. The engine uses a mechanical injection rocker and an integral Jacobs-style engine brake. After the set, the engine idles rough on cylinders 3 and 5, has a pronounced tick at the rear of the head, and the brake will not fully release on the rear three cylinders. Oil pressure is 22 psi hot idle (spec 18-30). The tech re-checks valve lash cold and finds all exhaust valves at 0.020 in (spec 0.024 in hot-adjusted on this engine family).
1. The tech concludes the rough idle and tick are caused by the exhaust valves being too tight. Evaluate that conclusion and describe the correct adjustment sequence and the most likely actual cause of the brake release problem.
Read the worked answer
The tight-lash conclusion is premature. Lash was checked cold against a hot spec; on this engine family the exhaust lash is set with the engine hot and running (or per the OEM hot procedure), so 0.020 cold does not prove the setting is wrong. Re-set lash per OEM: bring engine to operating temperature, use the injection-timing/valve-set sequence (TDC #1, adjust the intake/exhaust pairs listed for that position, rotate 360°, adjust the remainder), and torque the jam nuts to spec while holding the adjuster.
The brake release fault on the rear cylinders points to the engine brake slave-piston lash (the brake lash is set separately from valve lash) or to a mis-stacked rocker shaft - a rocker pedestal bolt torqued out of sequence, or a rocker installed on the wrong journal during reassembly, will hold the brake slave piston off its seat on the affected cylinders. Verify brake lash per OEM (typically ~0.015-0.025 in, engine-specific) and confirm each rocker is on its correct journal. The tick plus rough idle on 3 and 5 is more consistent with a bent pushrod or a rocker not seated on the pushrod cup after the head work than with lash alone.
2. Oil pressure is 22 psi hot idle. The tech wants to condemn the oil pump because the brake is sluggish. Is that justified, and what would you check first?
Read the worked answer
Not justified. 22 psi hot idle is inside the 18-30 psi spec, and engine-brake actuation is driven by oil pressure but is sensitive to the brake housing control valve, the solenoid, and the master/slave piston condition - not primarily to idle pressure. Condemning the pump on a within-spec reading is a parts-cannon diagnosis.
Check first: (1) brake on/off solenoid operation and control-valve screen for debris from the head work; (2) that the correct rocker shaft and oil feed passages are clear (gasket or RTV blocking a feed orifice is common after a reseal); (3) brake lash and slave-piston free travel; (4) verify oil pressure at the brake feed port, not just at the main gallery. Only after those are eliminated and a hot, loaded pressure test shows a real drop should the pump be considered.