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Knock in a 5.7 GMC

Discussion in 'Chevy Trucks' started by milwaukeevtwin, Dec 30, 2010.

  1. milwaukeevtwin

    milwaukeevtwin Senior Member
    Messages: 335

    I have a 1991 2500 gmc i have put about 2,000 miles on it since i bought it with no engine problems. Today it started up and i drove it about 5 miles with no problems and then started it to go home and about half way home i heard a clattering noise. Thought it was external untill i popped the hood. At idle it runs fine. Give it gas and you do not here it. If i give it a quick rap on the foot pedal i can here a clatter in the engine. Sounds like top of engine. I pulled drivers side valve cover to check out rockers and push rods and everything seems fine. On the the passengers side tomorrow. Any suggestions would help. Thinking maybe a lifter is sticking? It does not tick this is a clatter like something is coming loose?
    Please help! Thanks, Ron
  2. cubicinches

    cubicinches PlowSite.com Addict
    Messages: 1,415

    Sounds like a rod bearing to me. Cut the oil filter open... look for metallic debris.
  3. cubicinches

    cubicinches PlowSite.com Addict
    Messages: 1,415

    It might be tough for you to judge, but relatively speaking, is the noise fast or slow? The valvetrain operates at half of the crankshaft speed in terms of RPM... so valvetrain noises occur at half the rate of lower end noises.
  4. milwaukeevtwin

    milwaukeevtwin Senior Member
    Messages: 335


    Will have to check on this one. What dod i cut the filter with? Since cutting it with a saw will leave shavings? Just want to be able to tell what it is coming from me cutting or the engine? Thanks, This is good advise.
  5. cubicinches

    cubicinches PlowSite.com Addict
    Messages: 1,415

    They make a tool for cutting filters, kinda like a large tubing cutter. But if you use a chisel or screwdriver and hammer to make a hole in the side, near the top, you can finish the job with tin snips... just be careful, it's easy to cut up your fingers.

    Look for copper colored material in the pleats of the paper on the side facing the outside of the filter, as this is the direction the oil passes through the paper filter.
  6. Sydenstricker Landscaping

    Sydenstricker Landscaping PlowSite Veteran
    Messages: 3,882

    It could be one of the accessories on the engine. When the bearings died in my water pump in my 92 350 it was all chattery and loud. And no the pump did not leak either. I took a screwdriver and used it to listen to all the pulleys and that's how I narrowed it to the pump
  7. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    I use an air chisel to cut my filters open.
  8. Stan

    Stan Senior Member
    Messages: 579

    Any change in oil pressure?
  9. milwaukeevtwin

    milwaukeevtwin Senior Member
    Messages: 335


    Have a motor in another truck with low miles had a couple people look at they all say it is coming from lower end just going to swap it out for now. Wll check it out later. More time than money this week. LOL
  10. juspayme

    juspayme Senior Member
    Messages: 116

    sounds bad. change your oil if its gray coming out....not so good times..
  11. secret_weapon

    secret_weapon Senior Member
    Messages: 437

    If it is a rod knock, it might be the same thing what happened to my old chevy with 5.7

    It spun a cam bearing and starved one of the rods of oil.
    Don't just throw a set of bearings in it.
  12. South Seneca

    South Seneca Senior Member
    Messages: 474

    I had a 350 Chevy start making a tapping noise in the front of the motor. Most of the mechanics that heard it said it sounded like a wrist pin or a bad piston.

    Then one of my old stock car racing buddies told me to check the timing chain. The truck had 80k miles on it. When we pulled the timing cover it was missing 14 plastic teeth off the timing gears.
  13. auto tech

    auto tech Junior Member
    Messages: 12

    sounds like the flexplate bolts are loose or is cracked around the crank bolts take separate the flexplate from the torque converter see if it changes or at least check for cracks or loose bolts?