Fuel pump clicking

[D. Jones]

Just back from a test run to check for leaks after replacing my water pumps and thermostats. Everything looks good with that. I parked in the garage and went in and had a cup of coffee and when I went back out to the garage I heard a clicking noise coming from the engine compartment. I open the hood and used my stethoscope to locate the noise. It was my mechanical fuel pump making a medium rate rhythmic low tone series of clicks. Four or five clicks a very short break then four or five more. It kept this up for a few minutes. Never heard this before and I'm not sure what it means. Any ideas?

 

[WestCoast]

my guess is either the fuel pump rod is to short and causing the click as it hits the fuel pump arm, or the shaft pin holding the arm to the pump is worn and causing the click as the fuel pump lobe raises the arm on pump

 

[B-O-B]

I'm assuming the engine is off so that is probably the fuel leaking back into the tank.

 

[WestCoast]

LOL, B.O.B. that never occurred to me, leave it to me to do things the hard way, don't think about the easy explanations

 

[D. Jones]

I'm assuming the engine is off so that is probably the fuel leaking back into the tank.

Could be, and that was my first thought but then I remembered that there are two check valves in the pump that should keep fuel from going either way unless the pump is operating. My next thought was how much pressure would it take for that to happen and is it possible/probable. I need to think about the fuel circuit in the pump a bit to see if I come to any conclusions. Just a new puzzle to solve.

Thanks for your input.

 

[ford38v8]

From your clues, I have deduced the logical answer to your puzzle. You went on a test run, came back and shut down. Without air flow through the engine compartment, and without a constant flow of fuel cooling the pump, heat soak began vaporizing the highly volatile fuel causing an intermittent release of vapor pressure from the outlet valve, much like steam in a boiling pot will vibrate the lid. With pressures equalized, the tick of the valve is momentarily silenced until pressure builds once again to the level required to release once more. As all conditions must be correct to produce this entertaining phenomenon, the elusive ticking sound quickly ends the performance until next it finds those precise conditions present.
Elementary, my dear Watson.

 

[D. Jones]

From your clues, I have deduced the logical answer to your puzzle. You went on a test run, came back and shut down. Without air flow through the engine compartment, and without a constant flow of fuel cooling the pump, heat soak began vaporizing the highly volatile fuel causing an intermittent release of vapor pressure from the outlet valve, much like steam in a boiling pot will vibrate the lid. With pressures equalized, the tick of the valve is momentarily silenced until pressure builds once again to the level required to release once more. As all conditions must be correct to produce this entertaining phenomenon, the elusive ticking sound quickly ends the performance until next it finds those precise conditions present.
Elementary, my dear Watson.

Alan or should I say Holmes THANKS, I believe you may be on to something there. Hadn't thought about vapor pressure although I should have as I do have a small vapor lock problem on hot days when I shut the engine off and don't open the hood.

While it is not a major problem, just a minor irritation, I'm still looking for a solution to the vapor lock problem other than leaving the hood open when stopped.

Who has more fun than flathead owners. Answer no one!!!

 

[COE Dan]

I had to add a thermal spacer (I think I got mine from Dick Spadaro) between my carb and manifold on my '39 as the fuel in the carb bowl would boil when I shut the engine down. I could hear the bubbling and the increase in pressure would force the expanding fuel out through the idle jets. As the engine cooled down, the fuel would stop boiling but this would leave the carb bowl near empty and I could see fuel pooling on top of the throttle plates. This would cause problems starting (low fuel bowl supply and flooded cylinders).

The spacer eliminated this problem and minimized carb-related vaopr lock but I still have vapor lock issues in the lines/pump. When able, I use non-ethanol fuel. The ethanol in the fuel has a lower boiling point than gasoline is likely a contributor to this boiling fuel phenomenon.

Dan