While working on my fuel tank replacement project I've been finding
some other issues. While replacing the tank I've cleaned/rebuilt the
Racor 500FG, replaced all fuel lines with new (except HP fuel lines on
the engine), cleaned the bilge, and was going to inspect the Yanmar fuel pump.
Here's where the fun starts. When I took the fuel pump off I found the
casing to be cracked severely. It was cracked on the flange that mates
to the engine block. The pump has an arm that goes from that flange
area into the engine block and rides on a cam. As the cam rotates the
arm moves up and down, this is what causes the pumps diaphragm to move
up and down.
Pump Lower Casing Cracked
View of Crack From Fuel Pumps Operating Arm Flange
The good thing was that the marina next door had two replacement pumps
and associated gaskets in stock, and they were 70% off on top of that.
I got two $80 pumps for about $20 each the very day I needed them! One
went on the engine and the other in my spares stock.
With the new one on I decided to see just how this puppy works and
took apart the old damaged pump. What I found inside was scary. The
upper casing of the pump has an inlet valve, an outlet valve, a
fitting that keeps them in place, and two little screws to attach the
valve keeper. I found the valve keeper had failed and broken in two
pieces, the outlet valve was almost fallen out of place, and one of
the valve keeper screws out. The screw and broken piece were "floating
around" inside the pump beating the hell out of the diaphragm. If they
had broken the diaphragm, it would have filled the lube oil sump with
fuel oil by flowing down through the valves operating arm flange.
Pump Internal Damage
Loose Pieces Inside Pump, Damaging Diaphragm
That was a close one. The engine has run like this for who knows how
long. Give your engine a good look over.
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