Cummins/Onan NH-MS/1 / NH-S/1 — Fuel Pump Reconditioning
Repair & overhaul
For the Cummins/Onan NH-MS/1 / NH-S/1, from the Cummins/Onan service manual.
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Before you start
- Do not stretch the diaphragm when installing the cover.
Procedure
- Remove the fuel lines and mounting screws holding the pump to the engine.
- File an indicating mark across the union of the fuel pump bolt and cover; remove the assembly screws and upper pump body.
- Remove the valve plate screw and washer, then the valve retainer, valves, valve springs and valve gasket.
- Clean the pump body thoroughly with solvent and a fine wire brush.
- Place the new valve gasket in the cavity, assemble the valve spring and valves, reassemble the valve retainer and lock the retainer screw.
- Press down on the diaphragm to compress the spring under it, then turn the bracket 90° to unhook the diaphragm.
- Replace the diaphragm, fuel pump rod spring and diaphragm gasket; compress the spring and turn 90° to reconnect.
- Place the pump cover on the bracket with the indicating marks in line, insert the four screws, push the lever to its travel limit and hold while tightening.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
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.