Leak down test help

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  #1  
Old 09-26-16, 03:11 PM
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Leak down test help

Can someone help me with this? im having problems figuring this out. I bought a 5.3 lm7 supposedly had 80k miles on it. but i want to test it to make sure its worth my time to work on.

first i had a harbor freight tester was reading 20%+ leakage on all cylinders

now i have a snap on tester i bought second hand cause apprentey theyre the best and its telling me ive got 70% leakage on all cylinders

im having a hard time finding TDC on each cylinder.

so i dont know if its me the engine or the tester.
 
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  #2  
Old 09-26-16, 04:54 PM
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Leave all the plugs in except the cylinder you are testing. Turn the crank with a bar with your thumb on the plug hole until you are sure you are on compression stroke. If you can see in the plug hole you can usually tell when piston is at top of stroke; you may have to use a probe if you can't see the piston.

Attach the tester fitting and apply air. Then rock the crank back and forth a little to make sure rings are set; they need pressure against them to seal correctly. The air may push the piston down; this is why you leave the other plugs in (to help resist the force) you may have to resist with the bar. This is also why you want the piston at TDC as it best resists the air in that position.

It's not critical for the test that piston be at TDC, but it is critical that the piston not move during the test, and having it at TDC helps achieve that.
 
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Old 09-27-16, 07:05 AM
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Can you even test engine on stand hand cranking it? Presuming, that's what OP is doing. There is no crank power and speed, so what compression are we talking about?

https://www.youtube.com/watch?v=X_tbksFYhl4
 
  #4  
Old 09-27-16, 07:35 AM
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He's doing a leak down test, not a compression test. Air pressure is applied from a compressor, and the tester monitors how much the pressure drops as air leaks by the rings.....
 
  #5  
Old 09-27-16, 08:38 AM
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What readings did you get on the compression test? Usually a leakdown is done after to confirm and to identify where the leak is occurring (past rings, past valves, past gaskets...).
 
  #6  
Old 09-27-16, 11:10 AM
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Got it.

Put the vehicle in gear and set the parking brake to prevent the engine from turning when air is compressed into the cylinder. Start with the regulator turned counterclockwise to zero the incoming pressure. Connect compressed air. Turn the regulator clockwise to pressurize air into the cylinder.

Step 3 : Record leakage percentage for the cylinder. Remove the oil dipstick, radiator cap and oil filler cap. Open the throttle body or remove the air cleaner. Listen and watch. Wherever air is escaping will indicate where the problem is. Disconnect the gauge and move to the next cylinder.


Learned.
 
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