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Eccentric Wear?

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  • Fuel System: Eccentric Wear?

    I have a 259 cu in engine in a 60 Lark that I purchased about a year ago. The previous owner had absolutely no knowledge of what, if any, mechanical work may or may not have been done. When I test drove the vehicle it started, idled and drove around the block. However after going around the block and trying to accelerate in traffic it stalled, restarted, idled and stalled again. We chalked it up to either vapor lock (the car was in Nevada) or the fuel pump. The fuel pump was replaced and I purchased the car without test driving it again. Fast forward a year and I'm still having the same issues. I've drained the tank, blown the fuel line, replaced the pump (measuring vacuum and pressure before installing) replaced all hoses and made sure when the tank was drained it was clean inside. There is no screen on the inlet to the carb and I've replaced/removed the clear fuel filter the previous owner put on. I've borrowed a pump from a friend (1 new pump, one that came off the car (nearly new) and one from a friend who says it came off a running driving 259 and assures me it works. All three pumps provide a little fuel into the carb so the car starts and drives around the block but not enough for hard acceleration or higher speeds without stalling.

    I've decided to hold off removing the radiator, fan, water pump, etc. to measure the eccentric, which I read is supposed to have 0.485" of lift. I can see the eccentric with a mirror and well it looks like an eccentric but I haven't tried to measure it with the pump off. Any suggestions for how to measure the lift of the eccentric through the fuel pump arm inlet hole?

    I've fashioned another solution using the cover bracket on the end of the pump arm (see pics) and with two spacers the pump is bottoming out, one spacer improves flow but pressure is still below specification.

    My theory is that pump arm travel is reduced due to wear on the eccentric causing fuel starvation under load. With the two spacers added the pump is bottoming out, the question is what is the right thickness for the spacers to achieve correct vacuum and pressure?

    I'm guessing but I think the eccentric lift has been reduced to somewhere between 0.36" and 0.235" from 0.485" if each spacer is 0.125" thick. This seems like a lot of wear to me but I don't know if it is.

    The other two solutions as I see them are to pull off the radiator, fan, water pump, timing cover and valve covers and attempt to replace the eccentric. Or move to an electric fuel pump.

    With the spacers I'm concerned about additional wear to the eccentric or potential breakage. I don't know how long the spacers/pump would last and if they wouldn't accelerate the eccentric wear further. I don't relish the thought of tearing apart the the engine and I'm not sure if the cam would not have to be pulled in order to replace the eccentric.

    Questions: does anyone see any downside to temporarily using the spacer solution? How much work is it to replace the eccentric and does it require a part that is hard to source? Or does it require a new cam?

    Thanks for the advice!!

    Mike Click image for larger version

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  • #2
    The spacers will likely over stroke the Pump and damage the Diaphragm.
    The Fuel Pump Lobe unbolts from the Cam so not too bad of a job to replace it.

    I think I would test the Fuel System and Carb. with a temporary Electric Fuel Pump before going to the trouble of changing something that is not likely to be the fault.

    I have never heard a number for fuel pump arm lift, where did you get this 0.485"?
    Second Generation Stude Driver,
    Proud '54 Starliner Owner


    • #3
      It is far more likely that you have a pinhole in the fuel line from the tank to the pump. I have encountered this symptom many times : the tiniest pinhole, usually under a frame clamp, will let in a lot of air. You can plug one end and draw the other end down with a hand held vac pump to check. At the age of these cars, unless they came from the high desert, it is imperative to replace all tubing on the car.


      • #4
        Hi Rich, The lift number was posted in the thread, "Avanti fuel pump eccentric" along with several part numbers. Perhaps I misinterpreted that thread or mis-read it.
        You are correct, without grinding down the spacers from their current width in the picture I posted, the pump currently over strokes.
        I am trying to understand the benefit of installing a temporary electric pump and I'm probably missing your point. If the car runs and drives fine with the electric pump then I've eliminated all the other possibilities and it has to be the eccentric?


        • #5
          Hi Ross,
          Thanks, I believe I can perform that test and I will. Others have also suggested this. I want to believe it's not the cause as the car lived it's entire life in east central California and within a hundred miles or so of Reno in Nevada. It is a remarkably rust free Lark. When I show people they can't believe how clean it is. This is a simple test to run. Thank you.


          • #6
            It is always better to determine the actual cause of the problem before tearing into the car. Test, theorize, test, then test some more. Then attempt a repair.
            RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.

            17A-S2 - 50 Commander convertible
            10G-C1 - 51 Champion starlight coupe
            10G-Q4 - 51 Champion business coupe
            4H-K5 - 53 Commander starliner hardtop
            5H-D5 - 54 Commander Conestoga wagon
            56B-D4 - 56 Commander station wagon
            60V-L6 - 60 Lark convertible


            • #7
              I think the advice in post#3 is correct.
              Buy a 6 ft length of rubber fuel line and hook the tank directly to the fuel pump.
              This would be temporary , just to see if your gas line is the culprit.
              The pinhole is sometimes so small that gas does not leak out but air will be sucked in.


              • #8
                I second (or third) the pin hole theory. It could be a new hole or one that has grown bigger recently. I had exactly that symptom with a 59 Lark 259. It initially only was a problem going up hill with <1/4 of a tank, but slowly became more and more of a problem. The car always restarted and would sometimes get home without further problems. It was a pin hole in the fuel line under one of the clamps. Blowing air through the fuel line did NOT eject enough liquid gas to be seen, but did create enough odor to alert me to the problem.
                Skip Lackie


                • #9
                  I had some pin holes in my fuel line and I disconnected the metal line at the fuel pump and connected a long length of rubber hose and blew into it and sprayed soapy water over the line, there were bubbles at about three clasps. I replaced the entire fuel line.


                  • #10
                    Originally posted by Studenewbe View Post
                    /Cut/I am trying to understand the benefit of installing a temporary electric pump and I'm probably missing your point. If the car runs and drives fine with the electric pump then I've eliminated all the other possibilities and it has to be the eccentric?

                    OR... if it runs just as terrible as it did, it could be a steel Line, Flex Hose or Tank pick-up Tube obstruction.
                    Second Generation Stude Driver,
                    Proud '54 Starliner Owner


                    • #11
                      Thanks everyone for all the great suggestions and help. It has been frustrating running this to ground. Below is the list of what I've done. These are not in order (lesson learned: be more systematic when troubleshooting):

                      Bought a new fuel pump, borrowed a working pump, the Lark had a fuel pump in it that is less then two years old.
                      Tested output pressure while cranking engine of new and borrowed working pump, both were 2-3 psi.
                      Blew compressed air from inlet side of the pump to inlet side of tank, removing hoses so air blew through only hard line.
                      Changed all rubber hoses.
                      Drained gas tank, twice, and replaced fuel. No particulates or potential obstruction material was found.
                      Measured vacuum of new and borrowed pump on bench, 9" for both.
                      Installed rubber hose from gas tank to inlet of pump tying it off to the hard line running along the car. The Lark still acted as if it was starved for fuel when driven. No change.
                      Tested fuel flow on new and borrowed pump while cranking engine. Turning engine over for ten seconds filled an 8 oz. cup about 3/8 full for both pumps.
                      Retrofitted original pump with two 1/16" two spacers (see pictures), reinstalled and connected pump to the existing fuel lines (used existing hard line). Car ran and drove well with no fuel starvation. The pump was bottoming out however so one spaced was removed. Car continued to run well and pump bottoming out seemed to stop, i.e. no noise heard.

                      Conclusion: I've ordered an eccentric, lock washer and the associated gaskets required to change it.
                      When I have both eccentrics in hand I'll post pictures of the new one and the one pulled from the vehicle. I'll also attempt to take some measurements of both eccentics and post those.

                      Thanks again.


                      • #12
                        Jon Meyer told me that the problem with replacement fuel pumps is that the angle on the arm is wrong and it doesn't engage the cam correctly -too short a stroke=poor output-- I'm sure you could call him with your problem.