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Opinions on engine knock/rattle

Discussion in 'The Garage' started by Cricket, Apr 12, 2005.

  1. Cricket

    Cricket 3/4 ton status

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    Location:
    Colorado
    1977 350

    Stock with badger flat top pistons, elgin cam eqivalent to edelbrock 2102. No other internal mods. External mods are headers, edelbrock intake/carb.

    I have developed a knock/rattle that sound like a spray can when you shake it extremely fast. Only very audible when engine is cold in the morning. When I start the truck I get a quick rattle like a lifter is pumping up then it becomes quiet. You won't hear it again until you drive away and put a load on the motor, more gas = rattle, let of pedal and it disappears. When warm you can only hear it if you are me, it is so inaudible you have to know what you are listening for. It's coming from the passenger bank 2/4/6/8

    Oil pressure has always been good, 55psi at cruising, 18psi at idle. No fluctuations in the gauge, no overheating, does not use oil, no oil out of exhaust. Oil is clean, no water, no gas, no metal.

    It is very slowly getting worse over the months. I've always though it was the piston pin. Anyone else have any other ideas, I'd appreciate hearing them.

    ADDY: MSD ignition, timing is not overly advanced ie. spark knock.
     
  2. 79chevyk10

    79chevyk10 1/2 ton status

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    Sounds like rod knock to me. 18 psi at idle is good but a little low for a healthy motor. Drop the pan down and pull some rod caps off, if you see any copper.....crank kit time.
     
  3. Mad-Dog

    Mad-Dog 1/2 ton status

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    I'm gonna add my 2 cents and say that a piston pin could also be the culprit.
     
  4. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    A noise or rattle when you step on the gas is detonation. You might need to play with the timing and or run premium fuel. I would start by filling up with premium fuel and see if that helps the noise. If it does you are experiencing detonation for sure. Playing with the timing might make it go away. I have no idea what compression ratio you are currently at right now but anything over about 9.3/1 and lincorrect timing or low octane fuel and you will have detonation problems. You may need to address both timing and higher octane fuel to make the noise go away.
     
  5. Mad-Dog

    Mad-Dog 1/2 ton status

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    10 psi per 1000rpm is adequate....excessive oil pressure is just wasted HP
     

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