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Technical SBC fuel pump knock??

Discussion in 'The Hokey Ass Message Board' started by scrap metal 48, Jul 28, 2020.

  1. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 5,984

    scrap metal 48
    Member

    Loud knocking noise at fuel pump.. Removed new pump and the rocker arm has a soft resistance for about a 1/4" to 3/8" travel and then a lot of resistance the rest of the way.. I put the pump back up to the motor and very little effort to re install the bolts.. My question is, should the rocker arm have the same resistance through its entire travel?? The pump works fine and I have about 30 miles on the car and the knock is louder after warm up.. I pulled plug wires and the knock didn't go away.. Less noise if revved up(I think).. Any help or suggestions would be greatly appreciated...
     
  2. From memory, resistance should be same or similar through it's stroke. I had one SBC pump spring break a loop, and it provided a knock for me to diagnose. That little extra "slap" while bouncing off the pump pushrod and lobe, created the knock.
     
  3. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 989

    wheeltramp brian
    Member

    I had 2 do the same thing on a customer car.cheap junk parts.third one,a Carter fixed it
     
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  4. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 5,984

    scrap metal 48
    Member

    I will have to say I used a used push rod and a cheap new pump... I'll buy a better pump and new rod.. Just curious about the different resistance through out the pump rocker arm... As I remember, The pump arm was hard to push buy hand.. I can push the start of this pump's arm fairly easy and after about 3/8" of travel I can no longer push it in by hand and wonder if that is where the knock might be happening...
     
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  5. Wanderlust
    Joined: Oct 27, 2019
    Posts: 133

    Wanderlust

    Winner winner chicken dinner, cheap pump with a broken spring
     
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  6. nunattax
    Joined: Jan 10, 2011
    Posts: 2,290

    nunattax
    Member

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  7. bill gruendeman
    Joined: Jun 18, 2019
    Posts: 331

    bill gruendeman
    Member

    Aren't all sbc fuel pumps inexpensive? Haha Years Ago I had a rod knock on a Ford fe motor replaced the short block and still had the rod knock until I replaced the fuel pump. Live and learn.
     
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  8. Russco
    Joined: Nov 27, 2005
    Posts: 4,131

    Russco
    Member
    from Central IL

    I went through a spell where I was breaking the fulcrum arm pin loose in the pumps if I ran it real hard. Even on the Carter pumps, I could still drive home from the HAMB drags or Meltdowns on the broken pump but it would’nt get a full pump stroke in. The arms were just laid in a channel and “ peened ” over to hold them in place. Finally had to go with a expense Holley or Edelbrock that still ran the pin through an actual hole. Like they all used to.
     
  9. Dennis D
    Joined: May 2, 2009
    Posts: 620

    Dennis D
    Member

    Resistance should be the same throughout the stroke. D
     
  10. Put in a Nice Electric Rotor Fuel Pump in & you wont have any more
    problems.!

    Just my 3.5 cents

    Live Learn & Die a Fool
     
  11. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 5,984

    scrap metal 48
    Member

    Just put a new fuel pump and rod in and still has the knock.. SHIT.. I still here it the loudest at the pump.. I'm not sure what to do next.. I just drove it 25 miles and it runs fine, but has the knock at idle.. My oil light flickered once at a red light but went out when the light changed.. I'm running 10W30 Penn Grade oil... Would a straight 30W or 20W50 be better... I was hoping to have a beer this morning after what I thought was going to be the fix but just had another cup of coffee instead....
     
  12. I would be running 20w-50 myself anyway, but that's just me. Good luck, Milo. Hope it's nothing serious.
     
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  13. Dennis D
    Joined: May 2, 2009
    Posts: 620

    Dennis D
    Member

    I hate to even say this, but could the pump lobe on the cam be going away? D
     
  14. jaracer
    Joined: Oct 4, 2008
    Posts: 377

    jaracer
    Member

    The oil light it troubling. Most of those senders switch on at below 5 psi. My old 350 with 10W30 still has between 10 and 15 psi at idle after an extended highway run. I have a mechanical gauge.
     
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  15. Driver50x
    Joined: May 5, 2014
    Posts: 100

    Driver50x
    Member

    You might want to stick an oil pressure gauge on it and find out what the idle oil pressures actually is......
     
  16. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 5,984

    scrap metal 48
    Member

    Purchased a rebuilt engine off a guy I didn't know but believed to be honest.. Clean shop with clean tools on clean workbench with other engines in the process of being rebuilt.. I suppose the next step is to pull the pan and check the rod and main torques..Bottom end and heads were very clean and looked like a fresh engine... The idle is a little low in drive and the idiot light only flickered that one time.. I'll probably throw some heavier oil in it and drive it for the rest of the summer.. If it stays together I'll look at it this winter... If I find anything between now and then I'll let everyone know...
     
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  17. Okay then. Hate to keep throwing guesses out, but with low oil pressure(flickering light at idle), you might be at a lot of clearance on the front main bearing. Not excessive, just at the high side.
    When I "freshened" the 351W in my coupe, 25 years ago, I used STD bearings, and a high volume pump, on the recommendation of local shop owner. Clearances then, plastigaged at the upper end. I prefer using .001 under bearings to tighten up, but he said it would be okay. Always been lower oil pressure at idle, but okay. I've had a low knock the last couple of years, (at idle and warm) but .....
    It just keeps on going. I do use heavier oil too.
     
  18. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 5,984

    scrap metal 48
    Member

    I like ^^^ the last couple of years part...
     
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  19. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 5,984

    scrap metal 48
    Member

    Algoma56, Always been lower oil pressure at idle, but okay. I've had a low knock the last couple of years, (at idle and warm) but ..... I like this part....
     
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  20. Russco
    Joined: Nov 27, 2005
    Posts: 4,131

    Russco
    Member
    from Central IL

    If you don’t mind the expense take a sample of the oil when you drain it and send it in to have it analyzed. If your losing bearings or cam lobes it will show up. It’s about $30.00 to have it done. And you’ll get an email in a few days with results after they get it.
     
  21. MAD MIKE
    Joined: Aug 1, 2009
    Posts: 539

    MAD MIKE
    Member
    from 94577

    Verify your oil pressure switch is not leaking.
    Beg/Borrow/Steal a proper oil pressure gauge and verify actual pressure.
    Verify your timing chain isn't sloppy.
    • Rotated engine to 0°,
    • Remove distributor cap and watch the rotor,
    • Rotate(by hand) the crank backwards.
    • Once the rotor starts to move, stop.
    • Look down at the timing tab.
    • If you have <5° timing chain is OK.
    • If you have 6-10° timing chain is sloppy.
    • If you have >10° timing chain should be changed.
    A sloppy timing chain can knock against the block/timing cover and cause a knocking sound as well.

    Are there any other components bolted to that side of the block?

    Have you tried removing the belt and seeing if the noise subsides?

    Had an Olds with a knocking/clacking sound, PO had over tightened the belt that it fractured the multi-groove water pump pulley in the valley. It would make a nasty clanking sound. Took a while to figure it out.

    Bud had a slightly too long front engine mount bolt(or not thick enough washer), one that goes into fuel pump rod hole. It would cause the rod to hang up and then snap back and smack the camshaft fuel pump lobe. Pull that bolt and see if it has been self-clearanced.

    More drastic, remove pump/rod, blank off pump hole, start engine and see if the sound is still there.
     
  22. ^^^^^^This. Remove the pump and run it. Might need to rig up a small gravity tank to keep it running for a few minutes.
    Then start eliminating other possibles.
     
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  23. Work In Progress
    Joined: Dec 14, 2010
    Posts: 153

    Work In Progress
    Member

    Does it have a cam button installed? Chased a mysterious knock end ended up being a cam button. Take the timing cover off and run it.
     
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  24. scrap metal 48
    Joined: Sep 6, 2009
    Posts: 5,984

    scrap metal 48
    Member

    A lot of good suggestions here.. I ran the car with fuel pump removed but didn't run long enough to here anything.. The noise is hard to here upon start up.. It has to run a little while before I here it.. When hot it's really loud.. If I listen at timing cover I here NO noise.. It had new timing chain at rebuild(he says).. As I said before, if I put a broom handle to the fuel pump it's really loud.. If I place it where the vin pad is, I here it about half as loud.. Pulling plug wires still had noise.. I'm going to remove the fan belt and see if there is a change... I'm also going to put some 20w50 oil in it and see if the noise is less...
     
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