Why does my 350 knock for 3 seconds when I start it? Oil pump or worse?

Discussion in 'Small Block Tech' started by garybuick, Dec 25, 2014.

  1. garybuick

    garybuick Time Traveler

    When I start the car it has a deep knocking sound for about 2 to 4 seconds. As soon as pressure comes up on the gage the sound dissapears and doesnt return until the next time I start it.

    What is causing this problem? Is it a bad bearing or is the oil pump bad/weak, pickup tube blocked, oil filter clogged, gallery constricted with sludge. I dont know. Have you ever heard of this before?
     
  2. Mark Demko

    Mark Demko Well-Known Member

    Well I have heard engines, not just Buicks, knock a few seconds till oil pressure is established.
    It is usually from oil pressure not comming up quick enough, AND loose main bearing clearance.
    In other words, if the main clearance is within tolerance .0015 to .002 the crank shouldnt make any noise upon start-up, even without oil pressure for a few seconds as long as its not sent into fast idle right away.
    The presence of oil on the main bearings is sufficient until oil pressure is established and shouldnt make any noises, that is unless the engine is revved right away, or the clearance is excessive.
    Do you have an oil pressure guage hooked up?
    What are your HOT oil pressure readings at idle and what weight oil?
     
  3. garybuick

    garybuick Time Traveler

    I will do an oil change and get that information to you tomorrow when walmart opens back up. I do have an oil pressure gage hooked up. The noise goes away as soon as the needle starts showing pressure which takes 2 to 4 seconds. I live in florida the temp is moderate right now so I will use 10w 30 what do you advise?
     
  4. woodchuck2

    woodchuck2 Well-Known Member

    Dry start they call it. Almost every old Ford i have owned did it. The more tired the worse it was. That being said i beat them unmercifully with no issues. Only one FE big block did i ever get knocking badly but it never blew. Some of engines had no oil pressure at idle and maybe 5-7lbs when driving, knock like mad upon start up but still took their beatings.
     
  5. garybuick

    garybuick Time Traveler


    Ok I took it out for a ride and after it came up to operating temperature (190), at 600 rpm idle in drive the oil pressure was 22.5. At 900 rpm in park it was 30 and when I increase the rpm it went near 60 and wont go any higher. So what do you guys think? Bearing? or Pump, pickup tube, clogged filter. The car only has 55,000 miles on it.
     
  6. alec296

    alec296 i need another buick

    Pressure is good hot. More than likely have a weak lifter or not enough preload. Preload could be a rocker problems. Common if you have aluminum rocker arms.
     
    Ca GS joe likes this.
  7. garybuick

    garybuick Time Traveler

    it doesnt sound like lifter noise though. Its deeper, bottom end noise. not a tick or clack more like a knock. its a bigger noise. bigger metal hitting.
     
  8. sean Buick 76

    sean Buick 76 Buick Nut

    Consider finding another engine to rebuild and swap in if it really is the bottom end knocking What oil filter are you using? Some filters have anti-drain back issues, others are better.
     
  9. CJay

    CJay Supercar owner Staff Member

    Did you have thick oil in it? like 20W-50? If you do, it takes longer for the oil pressure to build because the oil is like molasses. When you start it cold, do you have the cold idle maybe set too high? Does it happen with 10W-30 too? And as a sidenote, use a quality oil filter like a WIX or Napa Gold
     
  10. alec296

    alec296 i need another buick

    Depending on sound yes it could still be collapsed lifter or rocker wear/low preload. Does it knock like a diesel engine? Chances are you would know if you have damaged a rod bearing. These engines do make some noise due to design and age. You mentioned 22 psi hot oil pressure running 10w30. If you have bearing issues you would not have that. Pull valve covers and check rear rockers for play.
     
  11. alec296

    alec296 i need another buick

    Could be main thrust bearing issues. But if it stops in 2-4 seconds after starting once oil pressure gets there its not a major problem.
     
  12. garybuick

    garybuick Time Traveler

    I use wix per the NAPA guys advice. I used to use AC Delco but they said wix is better.
     
  13. garybuick

    garybuick Time Traveler

    I may have 20w-50 in it. I thought that was better for hot florida summer. My neighbor alos cautioned me on that when he noticed the knock when we went to go look at rally wheels in Seminole FL
     
  14. CJay

    CJay Supercar owner Staff Member

    10w30 is just fine even in the hot Florida weather IMO
     
  15. garybuick

    garybuick Time Traveler

    I have actually been seriously considering this. Finding a running engine and swapping it, then start the rebuild. But I dont have funds for a full rebuild right now. What Id like to do is a compression test and leak down test, pull the pan and try to evaluate the overall health of the engine. But yes ultimately when I rebuild it that is what I would do.
     
  16. Mark Demko

    Mark Demko Well-Known Member

    If your hot idle pressure is over 20 lbs with 10/30 oil, I wouldnt do anything, except try another filter.
     
  17. Smartin

    Smartin antiqueautomotiveservice.com Staff Member

    Hot oil pressure is better gauged once the OIL is hot...coolant temp doesn't necessarily coincide with oil temps. I would drive the car for 20 minutes or so, and then check oil pressure at idle. You will probably see that it's a bit lower than previously mentioned.

    If your oil pressure is good and it doesn't make noise while running, then you can check the oil filter and some other easy stuff. Otherwise, I would just drive it. If you're really bugged by it, then you could rip it out of the car...but unless you're hell-bent of rebuilding it, then just accept it as it is.

    I noticed you're looking to pull the oil pan...that is never a bad idea to check the pan for sludge and blockages at the screen.

    I know several guys with BBB's that had been gone through, and still had a knock for the first few seconds until oil pressure built up. Yay for old cars!:error::beers2:
     
  18. Fox's Den

    Fox's Den 355Xrs

    Use half 10w-30 mobile 1 and 15w-50 mobile 1 and you will be good to go. Your motor might be a litle loose but I wouldn't worry about it until it got worse. Your oil pressure is good and the mobile 1 synthetic will keep you running a long time. My motor is 20 years old now and this is what I use and nothing else. I use the wix filter too.
     
  19. 8ad-f85

    8ad-f85 Well-Known Member

    Are you positive it isn't piston slap that goes away as soon as oil is slung around?
     
  20. garybuick

    garybuick Time Traveler

    Are you saying you know guys who spent thousand completely rebuilding their engines to aircraft standards mint and the engine still rattles when it starts?
     

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