Replacing a broken fuel pump

leaking Yanmar fuel pump

From a Small Leak to Major Repair

While adjusting the engine idle, a small leak was noticed near the fuel pump.  All fuel lines and fittings seemed to check out fine.   The leak initial appeared to be coming from the gasket within the fuel pump (see photo).  The area was cleaned well and dry paper towels were wrapped around the pump and fuel fittings.   After running the engine for several minutes, the leak was discovered to be engine oil leaking from the fuel pump engine mounting gasket.  An easy fix.


The fuel pump was immediately removed, but it came off without the pump lever arm which had apparently broken off inside the gear case cover.  Below is a photo of the broken fuel pump, next to it is a photo of what the fuel pump should look like.

Yanmar fuel pump with missing lever

image a new Yanmar fuel pump

Yanmar 3QM30 gear case schematic.  

Cracking the Case

 The front gear case is not directly connected to oil sump of the engine block.  So this meant that when the broken lever dropped down it remained within the front part of the engine gear case.  Looking at the schematic from the 3QM30 parts manual reveals that broken part was likely sitting under the gear for the oil pump.  See diagram.  With there being some possibility of the broken lever getting caught into the gears and creating a big problem, the broken lever had to be removed before installing a new fuel pump and starting the engine.

First,  retrieving the broken lever by fishing with a telescoping magnet pickup was attempted.  But after many attempts and modifications to the telescoping magnet setup, trying to retrieve the pump lever with a magnet failed.

harmonic balancer pulley

Next, was the removal of the gear case cover.  This involved removing the alternator, the lift muffler, oil filter, and water pump hoses.  Pulling the harmonic balancer pulley was a challenge as there was only a few inches between the fuel tank and the pulley.  The gear case cover was only partially separated/removed  as to fully remove it would requires disconnecting the governor arm (which is a greater challenge by several, several orders of magnitude).

Once all the case bolts were loosened, the case lifted away from the block releasing about 1/4 cup of oil and the broken lever.  Fortunately, the case gasket was not broken, and after a quick clean, the case cover was reinstalled.

fuel pump mounting location on gear case

gear case shown from the oil filter side  

fuel pump with broken lever

front of gear case

Finishing up

 At this point, a new fuel pump and gasket were installed, and the fuel lines bled.  Reinstalling the harmonic pulley was a challenge due to the confined space.  Normally, the pulley is hammered onto the crank shaft and then bolted with a cap bolt.   The crank shaft has about 1" of tapped M12x1.25pitch threads but the collar of the pulley is approximately 2" long.    To aid in the installation of the harmonic pulley, a M12x1.25x70mm cap screw was purchased from Fastenal.

To install, the shaft key was aligned to the harmonic pulley and the cap screw was slowly tightened to pull the harmonic pulley onto the shaft.  A photo was taken to check the shaft key alignment to the harmonic pulley(see photo below).  The cap screw was longer than needed, so washers were used to fill extra space.   A lead mallet was used to tap on the harmonic pulley in combination with tightening the end cap screw.   The last 1/2" of installation was done using the original cap bolt.

aligning the pulley to the crank

measuring pulley/case distance