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No Compression

Discussion in 'The Garage' started by Rocky91, Jul 20, 2002.

  1. Rocky91

    Rocky91 Registered Member

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    I have a '91 TBI 350 that is showing no compression in the #6 cylinder. I took the valve cover off and every thing seemed to be moving like it should. Are there any other causes of lost compression other than a burned valve or bad piston ring? I'm assuming that the piston rings and head gasket are good cause I think they would show atleast a little compression. Before I pull the head off to check it out, is there anything else that I could try to check or that could cause this? Thanks.
     
  2. FLASHLIGHT76

    FLASHLIGHT76 1/2 ton status

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    DRAIN YOUR OIL AND CHECK IT FOR FUEL. YOU MIGHT HAVE A HOLE IN YOUR PISTON. BUT IF THERE IS FUEL IN YOUR OIL IT'S A GOOD SIGN OF RING OR PISTON WEAR. IF IT WAS A HEAD GASKET YOU WOULD LIKELY HAVE COOLANT IN YOUR CYLINDER. LOOK AT YOUR PLUGS AND SEE WHATS ON THEM. THAT WILL BE YOUR BEST CLUE.
     
  3. FLASHLIGHT76

    FLASHLIGHT76 1/2 ton status

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    JUST THOUGHT ABOUT SOMETHING. TRY TO GET YOUR HANDS ON A CYLINDER SCOPE. YOU MIGHT BE ABLE TO RENT ONE FORM A PARTS STORE. IT WILL LET YOU LOOK IN THROUGH THE SPARK PLUG HOLE AND SEE WHAT THE WALLS OF THE CYLINDER LOOK LIKE.
     
  4. Rocky91

    Rocky91 Registered Member

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    Thanks for the responses. I did check the spark plugs, 7 had no abnormalities, but the bad cylinder did have some deposits on the electrode that looked like pieces of metal. I just changed the oil the other day but didn't see anything odd with it. I'm pulling the head off first thing in the morning so I will check out the cylinder wall. What else should I look for?
     
  5. Thumper

    Thumper 1/2 ton status

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    You can squirt some oil into the cylinder to see if the compression changes. If it increases, you know its a ring. If it doesnt change its prolly top end.

    Mike
     
  6. mdm365

    mdm365 1/2 ton status

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    been at this stuff awile and all the ideas are good but one sure fire way is to put air in the cyl there is a gauge that you can buy that is called a leak down tester summet sells this. the gauge has two gauges one is the amount the compresser puts out and the other is the pressure that goes in the cyl how ever you can adapt a hose (I used a compression gauge hose and went from there).you only need about 20 lbs in the cyl put the cyl you are working at top dead center intake and exaust should be closed put the air to it now what you do is listen for the air if you have a bad valve,intake will come out the carb if the exaust is bad it will come out the exaust pipe. if you have a hole in the piston or bad rings you will here the air in the crank case.I even seen one shoot the dipstick out that was a hole in the piston. also if there is a bad head gasket or a crack
    in the water jacket you will get bubbles in the radiator.if you got a break in the heag gasket inbetween a cyl you can find this by putting a compression to the next cyl and the gauge will move from the air passing over through the break in the head gasket to the other cyl.If you have gas in your oil do your self a faver and look hard at the fule pump the diafram mostlikly has a hole in it and leaking into your motor.I use this all the time works good.I hope this will help if you dont have a compressor my be you cand get a buddy to help you out i have a small one at home and works fine for this. good luck mike
     

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