Cummins/Onan GTA50 Engine

⚠ Never adjust the power valve screw more than 1/4 turn (90 degrees) at a time.

⚠ Do not exceed 20 inches of water to the on-engine gas flow regulator.

Tools: Water manometers, Pyrometer, Oxygen meter, Timing light

1. Install water manometers at on-engine gas regulator and carburetor.
2. Set gas pressure to on-engine regulator 10-20 in H2O at full load.
3. Set carburetor gas pressure 4-6 in H2O at full load.
4. Set initial timing: GTA38 20-24 DBTDC, GTA50 19-21 DBTDC.
5. Install pyrometer below turbo flange, 0-30 psi gauge on manifold, oxygen meter in turbo outlet.
6. Connect timing light to #1 cylinder.
7. At full load, adjust both carburetor power valves for lowest exhaust temperature.
8. Retard/advance timing in 2 degree increments to find lowest EGT and boost without RPM loss.

⚠ Read the entire overhead adjustment procedure before starting.

⚠ Using wrong flywheel index marks (A or C) will damage push rods.

Tools: Feeler gauges, Inch-pound torque wrench 3376592, Torque wrench adapter ST-669

1. Disconnect battery; remove valve covers (gaskets reusable if undamaged).
2. Tighten rocker lever shaft cap-screws to 156 Nm [115 ft-lb].
3. Make cross-head adjustment before valve adjustment.
4. Loosen cross-head lock-nuts; turn adjusting screw out one turn.
5. Hold cross-head against guide; turn screw in until it touches valve stem.
6. Tighten cross-head lock-nut: 35 Nm [25 ft-lb] with ST-669, 40 Nm [30 ft-lb] without.
7. Set exhaust lash 0.89 mm [0.035 in]; intake lash 0.36 mm [0.014 in].
8. Tighten adjusting screw to 0.68 Nm [6 in-lb] or to slight feeler drag.
9. Tighten valve lock-nut: 45 Nm [35 ft-lb] with ST-669, 60 Nm [45 ft-lb] without.
10. Recheck feeler drag; recheck all lock-nuts; install valve covers.

⚠ Cylinder pressure between engines may vary by as much as 40 psi.

Tools: Compression gauge, Spark plug removal tool

1. Verify batteries are fully charged; shut off and tag the gas fuel valve.
2. Ground the ignition G lead to prevent ignition spark.
3. Remove spark plug probes; clean any oil/water contamination.
4. Remove spark plugs from all cylinders using a proper tool.
5. Block throttle wide open; install compression gauge in #1 cylinder.
6. Crank engine until it has rotated 6 to 8 revolutions and gauge is stable.
7. Record the reading in pounds per square inch.
8. Repeat for each cylinder.
9. Average all cylinder pressures; all cylinders must be within +/-5% of average.

⚠ CNGE does not recommend cleaning paper type air cleaner elements.

⚠ Never operate the engine without an air cleaner.

1. Remove wing nut securing the air cleaner element cover.
2. Remove the cover.
3. Pull the element out without damaging it.
4. Remove gasket or O-ring seal from outlet end of housing.
5. Inspect seal and replace if necessary.
6. Remove inner safety element and replace if required.
7. Install new element.
8. Assemble cover to housing.

⚠ Do not remove the radiator cap from a hot engine.

⚠ Severe engine damage will result if the valve is left closed.

1. Turn the coolant filter head shutoff valve to the Off (horizontal) position.
2. Remove and discard coolant filter; clean gasket surface on filter head.
3. Apply light film of Lubriplate 105 to coolant filter gasket.
4. Install filter as specified by the manufacturer.
5. Open the shut-off valve and install the pressure cap.
6. Operate engine until coolant is above 82C [180F]; check for leaks.
7. Check coolant level after air is purged.

⚠ Avoid direct contact of hot oil with your skin.

⚠ Pre-lube the engine or crank with manual fuel valve off until oil pressure appears.

Tools: Oil filter wrench 1 1/8-1 3/16 in, 1 1/4 in wrench or socket, Pipe cutter or hacksaw

1. Operate engine until coolant reaches 60C [140F], then shut off and remove oil drain plug.
2. Clean around oil filter head; remove filter with 1 1/8 to 1 3/16 in wrench.
3. Make sure correct full-flow filter is installed (1 1/2-16 in threads).
4. Fill new filter with clean lubricating oil.
5. Coat gasket sealing surface with a light film of oil.
6. Install filter as specified by the filter manufacturer.
7. Install oil drain plug; torque 100 Nm [75 ft-lb].
8. Fill engine to proper level with recommended oil.
9. Operate at idle and inspect for leaks.
10. Stop engine, wait 5 minutes, check level and add to H mark.

⚠ Mechanical over-tightening can damage the sparkplug and cylinder head.

⚠ Never lubricate the threads of the sparkplug.

Tools: Magnetic sparkplug socket Snap-On S971KA, Torque wrench

1. Make sure porcelain is clean; do not touch the porcelain area.
2. Thread plug in by hand using extension and magnetic socket S971KA.
3. Turn clockwise to tighten.
4. Torque to 35 to 41 Nm [26 to 30 ft-lb].
5. Apply dielectric grease inside and outside the sparkplug boot.
6. Press boot down until a snap is felt.

Tools: 5/8 in deep-well sparkplug socket

1. Disconnect wire from ignition coil end first, then from sparkplug end.
2. Remove rubber insert from sparkplug socket to prevent contamination.
3. Use 15.875 mm (5/8 in) deep-well rubber insert sparkplug socket to loosen plug.
4. Continue turning counterclockwise until threads disengage.
5. Lift sparkplug out of adapter without dropping it.
6. Mark or tag each sparkplug with its cylinder number.
7. Inspect plug wires, extenders and connections for corrosion or arcing.

⚠ Excess moisture or temperature in the sample will damage the O2 cell.

Tools: Teledyne Model 320P/320P-D oxygen meter, 3/8 in copper or stainless tubing

1. Read manufacturer's manuals for initial startup.
2. Check battery condition before each use; recharge if low (overnight, 14 hours).
3. Check filter material; change if wet or dirty.
4. Calibrate with ambient air (20.9% O2); install flow-through adapter cap.
5. Connect temperature reducing tubing to engine exhaust system.
6. Coil tubing several times or make a dip to act as a water trap.
7. Depress pump button to pull exhaust sample; draw no longer than 5 minutes.
8. Clear the water trap every 10 minutes.
9. After each 5 minutes sampling, purge with clean ambient air to near 20.9%.
10. Turn off unit and reinstall cell saver cap when not in use.

⚠ Cap-screws threaded into aluminum may require torque reductions of 30% or more.

Tools: 3/4 in wrenches, 7/16 in wrench, 9/16 in wrench, 15 in pipe wrench

1. Disconnect battery power; turn off and tag manual gas shut-off valve.
2. Loosen 2 in pipe coupling below RV91 regulator; disconnect ASCO valve.
3. Remove band clamp from turbocharger inlet and carburetor outlet pipe.
4. Remove carburetor air/fuel outlet pipe (six 1/2 in bolts); do not reuse gasket.
5. Remove RV91 regulator from carburetor with a 15 in pipe wrench.
6. Remove 600D carburetor (four 1/4 in and six 3/8 in bolts).
7. Install 600D carburetor; 3/8 in bolts to 24 Nm [18 ft-lb]; 1/4 in bolts to 7 Nm [5 ft-lb].
8. Install 2 in inlet pipe with pipe sealant; tighten one full turn.
9. Install outlet pipe and gasket with silicone sealant; six 1/2 in bolts to 53 Nm [39 ft-lb].
10. Install band clamp on turbocharger inlet hose.
11. Reconnect coupling and battery; open manual gas valve.
12. Check all fittings for gas leaks.

⚠ The fan belt idler is under tension. Do not allow hands between the idler and the belt.

Tools: 8 point socket, Breaker bar

1. Remove the fan idler shock absorber.
2. Use 8-point socket/breaker bar to hold the idler against spring tension.
3. Remove the cap-screw and slowly relieve spring tension.
4. Remove the fan belt.
5. Inspect the belt for cracks, glazing, tears or cuts.
6. Install the belt.
7. Rotate the idler against spring tension until cap-screw holes align.
8. Install cap-screws; torque 45 Nm [85 ft-lb].
9. Turn wrench until the idler is against the belt.
10. Install the shock absorber.

⚠ GTA50 must use the K50 thermostat with vulcanized nitrile rubber seat.

Tools: Seal driver 3375411, Mallet

1. Disconnect the negative battery cable.
2. Drain cooling system to just below the thermostat housing.
3. Remove both upper radiator hoses from the thermostat housing.
4. Remove the twelve cap-screws; remove thermostat housing and gasket.
5. Remove the thermostats and seals.
6. Clean and inspect housing for cracks, pitting or damage.
7. Check thermostat operation; install seal with part number up.
8. Install seal with mallet and driver 3375411 (max 0.51 mm below cast edge).
9. Install thermostat by pushing on the outer rim.
10. Install new gasket, housing and cap-screws; torque 45 Nm [35 ft-lb].
11. Install upper radiator hoses; tighten clamps to 6 Nm [50 in-lb].