Thread: leak down test

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when using a leakdown tester such as this, how do you know whether or not it is weak rings, cylinders, valves, gaskets? Or does it just tell you there is a leak somewhere in the system as a whole?

Test it with the cylinder at TDC, then at BDC and compare the readings.....If it's 4% at TDC and 10% at BDC it would indicate bad rings... If it's equal at the top and bottom, then listen at the headers and at the carb to determine which is leaking.

thanks for the reply Dave, the kit says it checks it all. And I was for sure going to have to know how to tell what was what. (Oh wait Houston we have a problem). Thanks also Dave, we have the dual unit posted.

Originally Posted by mooneye777

thanks for the reply Dave, the kit says it checks it all. And I was for sure going to have to know how to tell what was what. (Oh wait Houston we have a problem). Thanks also Dave, we have the dual unit posted.

I've found a good, tight engine will come in at 5% or less leakdown....I test mine at 90PSI. We have zero gap 2nd rings in both the drag cars, they stay at around 1% to 2%.....

Another test I do is to crank the regulator down to about 20 psi and pull the piston from BDC to TDC in the normal rotation direction and see if there are any bad spots in the cylinder..... Sometimes will indicate an area in the cylinder that maybe the hone isn't quite right, or perhaps a bit out of round....... Heck, I've even used the leak down tester with a bunch of plugs and plates to pressure test a block or heads (Cigarette smoke works great as a leak detector when things are pressurized with air)...Also with a few fittings it works great to leak check all the lines and fittings on the car before they have fluids in them....When you're setting valves, a leak down tester will let you know when the other valve is open.... Heck, be creative with it!!!!!!! Lots of uses and procedures besides just what it was designed for!!!!

Probably not a lot of that stuff in the instruction sheet either, just some things I've tried and actually had work!!!!!

For those of you that run blown cars,...don't leave the breaker bar in the top blower pulley and turn on the air.

Don't ask how I know.

Originally Posted by bentwings

For those of you that run blown cars,...don't leave the breaker bar in the top blower pulley and turn on the air.

Don't ask how I know.

Spent some time as a hired gun in a Top Alcohol car....seen that done before... Did you lose any teeth or just a big lump on your head??????

[QUOTE=Dave Severson] (Cigarette smoke works great as a leak detector when things are pressurized with air)

That brings back a memory. At work one day we were mig welding with brass wire. It really throws the molten weld balls. A friend of mine got a braze ball in his ear, and it burned a hole in his ear canal. For a month or so after, everytime he smoked, you could see smoke come out of his ear. Thanks for the memory Dave.

Originally Posted by Dave Severson

Test it with the cylinder at TDC, then at BDC and compare the readings.....If it's 4% at TDC and 10% at BDC it would indicate bad rings... If it's equal at the top and bottom, then listen at the headers and at the carb to determine which is leaking.

Might not be what the book sez, just what works for me.......

I never used to use the tester, just screw an air fitting in a plug hole and listen, intake, exhaust, and crankcase breather. Any great amount of hissing shows up any problems.