Cummins/Onan GTA38 / GTA50 — Intake & Exhaust Valve Adjustment
Adjustments · Cylinder head / valve train
For the Cummins/Onan GTA38 / GTA50, from the Cummins/Onan owner's manual.
Applies to: Cummins/Onan GTA38 engine, Cummins/Onan GTA50 engine
Before you start
- Read the entire overhead adjustment procedure before starting.
- Using wrong flywheel index marks (A or C) will damage push rods.
Procedure
- Disconnect battery; remove valve covers (gaskets reusable if undamaged).
- Tighten rocker lever shaft cap-screws to 156 Nm [115 ft-lb].
- Make cross-head adjustment before valve adjustment.
- Loosen cross-head lock-nuts; turn adjusting screw out one turn.
- Hold cross-head against guide; turn screw in until it touches valve stem.
- Tighten cross-head lock-nut: 35 Nm [25 ft-lb] with ST-669, 40 Nm [30 ft-lb] without.
- Set exhaust lash 0.89 mm [0.035 in]; intake lash 0.36 mm [0.014 in].
- Tighten adjusting screw to 0.68 Nm [6 in-lb] or to slight feeler drag.
- Tighten valve lock-nut: 45 Nm [35 ft-lb] with ST-669, 60 Nm [45 ft-lb] without.
- Recheck feeler drag; recheck all lock-nuts; install valve covers.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Exhaust 0.89 mm [0.035 in]
- Intake 0.36 mm [0.014 in]
- Rocker shaft 156 Nm [115 ft-lb]
Source: Cummins/Onan owner's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.