Onan (Onan Division of Studebaker Corporation, Minneapolis, Minnesota) Spec T Generator Set

⚠ If the screw is tightened more than one turn, the exhaust valve could hit the piston

Tools: Feeler gauge

1. Set valves for correct clearance first.
2. Leave flywheel at 10 to 45 degrees ATC with piston on power stroke.
3. Set arm in decompression position; turn setscrew until it just touches exhaust rocker arm.
4. Turn the screw exactly one revolution clockwise.
5. Hold setscrew and tighten lock nut 1/4 to 1/2 turn past finger tightness.

Tools: Screwdriver

1. Hold the sensitivity stud in place with a screwdriver.
2. Change spring tension with the speed adjusting nut.
3. More tension gives more speed.
4. To adjust high speed of solenoid two-speed governors, change solenoid rod length.

⚠ Check valve clearance when the engine is at room temperature about 70 F

Tools: Feeler gauge, Socket wrench, Rocker arm wrench

1. Turn the flywheel until the cylinder is on its compression stroke.
2. Turn the flywheel clockwise an additional 10 to 45 degrees.
3. Loosen the rocker arm locknut to increase clearance, tighten to reduce clearance.
4. Check clearance with a feeler gauge between rocker arm and valve.
5. Set clearance to 0.011 inch intake and 0.008 inch exhaust.

⚠ Injection pump must be timed on the compression stroke, not the exhaust stroke

Tools: Depth micrometer

1. Install pump tappet in its recess and position flywheel on port closing mark of compression stroke.
2. Measure distance from pump mounting pad to tappet center with a depth micrometer.
3. Subtract that depth from the pump port closing dimension of 1.670 inch.
4. Result is the shim thickness required; shims vary from 0.006 to 0.052 inch.
5. Select the correct shims and install the pump.

⚠ Injection pump must be timed on the compression stroke, not the exhaust stroke

1. Install pump with 0.006-inch shims between pump and pad.
2. Loosen the delivery valve holder to relieve pressure on the spring.
3. Rotate the flywheel to about 15 degrees before the port closing point.
4. Blow in the pump inlet and rotate flywheel clockwise until air stops leaving the outlet.
5. Measure the distance to the PC mark and select shims from the chart.
6. Install the pump.

1. Open the air bleed screw on top of the secondary filter.
2. Operate the hand priming lever on the transfer pump.
3. Continue until no air bubbles flow from the bleed screw hole.
4. Tighten the bleed screw and return the priming lever to its original position.
5. If the transfer pump cam lobe is on the high side, turn engine one revolution before priming.

1. Place a pan under the old filter and remove it by turning counterclockwise.
2. Clean the filter mounting area.
3. Oil the new filter gasket and screw the filter on clockwise until the gasket touches the base.
4. Tighten 1/2 turn more.

⚠ Always replace cap tightly or oil leakage may occur

1. Remove hose clamp, breather hose, insulator clamp, insulator halves and breather cap clamp.
2. Wash cap, valve assembly and baffle in suitable solvent.
3. Reinstall.

⚠ Do not use ether starting aids; ether is extremely explosive

1. Check the engine has been filled with oil and fuel.
2. Prime a dry fuel system and return the priming lever to the disengaged position.
3. Preheat for 20 seconds in ambients above 55 F.
4. Hold preheat switch, push fuel solenoid ON, press START.
5. Release start switch after engine starts and reaches speed.
6. Oil pressure should read at least 20 psi.

⚠ Do not pry the body apart; this would damage the diaphragm

Tools: Screwdriver, File

1. Remove pump inlet and outlet lines and the two cap screws; lift the pump off.
2. Notch the pump cover and body with a file for correct reassembly.
3. Remove the six screws and tap the body with a screwdriver to separate.
4. Lift out the diaphragm assembly and diaphragm spring.

Tools: Torque wrench

1. Install the head assembly and gasket to the cylinder block.
2. Tighten head bolts clockwise starting with the 12 o'clock position.
3. Follow the order around the clockface, finishing at the 10 o'clock position.
4. Torque the bolts evenly to 44-46 ft-lbs.
5. After the first 50 hours, retighten the cylinder head bolts and check valve clearance.

⚠ A dirty mounting surface could permit blow-by causing nozzle failure and power loss

1. Install a new heat shield to head gasket in the cylinder head recess.
2. Install the heat shield, a new nozzle gasket and the nozzle adapter.
3. Insert the nozzle assembly into the recess; do not strike the tip.
4. Install the nozzle flange and two cap screws, tightening alternately to 20-21 ft-lbs.