Cummins/Onan — Flow Timing Injection Pump
Adjustments
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Do not permit any flame, cigarette or other igniter near the fuel system.
Procedure
- Install No. 12 timing button in new injection pump; remove delivery valve cap nut and holder, take out spring and replace valve holder and cap nut.
- Install new injection pump.
- Remove No. 1 injection line; install line with top end in pump outlet and place open container under open end.
- Disconnect governor linkage at ball joint and hold control arm up at maximum fuel position.
- Rotate flywheel clockwise to point where PC mark is about 15 degrees before timing pointer (compression stroke of No. 1 cylinder).
- Manually operate transfer pump until fuel free of air flows from open end of No. 1 injection line.
- Continue operating transfer pump while rotating flywheel slowly clockwise; stop at exact point fuel stops flowing (one drop in 2 to 5 seconds allowed).
- Mark flywheel in 0.1 inch graduations from PC mark if timing is incorrect.
- Multiply distance measured times .003 inch (0.76 mm) to determine new button thickness difference.
- Install correct button and reinstall injection pump.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- One degree of crankshaft rotation equals 0.1 inch graduation or .003 inch button thickness
Source: Cummins/Onan service 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.