Leakdown Test ???
Thread Starter
Melting Slicks
Joined: Feb 2003
Posts: 2,330
Likes: 6
From: Long Island NY
Leakdown Test ???
I'm preforming my first leakdown test. A little background. I'm going through 1 qt. per hour . 3 plugs are oil soaked (2,4,& 8). I started with #8 and had 50% leak and when I moved the piston a little it dropped to 30% still bad. My question is how loud is the air I'm listening for? Even at 50% the leak didn't sound noticeable anywhere. At the carb, the tailpipe or the oil cap. Also this test will Not tell if the intake manifold is the problem (I already re-gasketed it). I'm sure the rings are bad, but I just ant to be sure.
Melting Slicks
Joined: Dec 2000
Posts: 3,407
Likes: 2
From: Carmichael CA
Leak down will help detect which cylinders have worn or damaged rings, but it won't detect leaking valve stem seals or valve stem guides which seem to be the most likely oil leakage sources. If you have oil soaked spark plugs then you probably have oil leaking in from the valve stems. Only a small amount of oil manages to find it's way into the combustion chamber through the rings...not enough to "soak" your plugs. You can replace the valve stem seals and measure the diameter of the valve stems with the head still attached by rotating the engine with a socket on the dampener bolt until the piston is at TDC at the top of the compression stroke for the cylinder that you want to work on. Then, you can safely remove the valve springs...the valves will fall down about 1/4" to 1/2" into the combustion chamber and rest there until you finish working on that cylinder.
Keep us posted.
Keep us posted.
Thread Starter
Melting Slicks
Joined: Feb 2003
Posts: 2,330
Likes: 6
From: Long Island NY
I already replaced the valves seals with o-rings and umbrella seals. That's why it's either broken rings on 3 cylinders or maybe a crack in the intake manifold or very worn valve guides... I just want to know how loud of a hiss I'm supposed to hear with the leakdown test...
Drifting
Joined: Jan 2002
Posts: 1,663
Likes: 139
From: Vail AZ
With 50% leakdown you should hear "something." Loudness is subjective, but you should be able to hear something, somewhere. But whatever the case, I'm thinking your wallet will soon be hissing rather noticably. Hope I'm wrong, but I think your engine is destined to see some bench time.
Melting Slicks
Joined: Dec 2000
Posts: 3,407
Likes: 2
From: Carmichael CA
I just don't see 1 Qt per hour getting sucked into the combustion chambers just from the film on the cylinder walls even if all your pistons had like 1/4" gaps in the rings. That is a lot of oil man. But, hey...I learn something new every day.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
Good engines will leak in the high 90%. Once warmed up that could also go to near zero if a valve is tweaked as spring pressure and heat will straighten it out. They will check intake, exaust, and rings by listening to the source. A intake leak will be observed by opening the butterflys. Likewise past the rings will be heard from the oil pan. And exhaust will be from the headers or exhaust pipes. A strong air compressor will also help in this operation. Often used on barrel valves too in a FI equiped piece. Very good racers tool.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Originally Posted by Ironcross
Good engines will leak in the high 90%. Once warmed up that could also go to near zero if a valve is tweaked as spring pressure and heat will straighten it out. They will check intake, exaust, and rings by listening to the source. A intake leak will be observed by opening the butterflys. Likewise past the rings will be heard from the oil pan. And exhaust will be from the headers or exhaust pipes. A strong air compressor will also help in this operation. Often used on barrel valves too in a FI equiped piece. Very good racers tool.
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Le Mans Master
Joined: Apr 2006
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Originally Posted by Ironcross
That statement couldn`t be further from the truth! 
time, oh I forgot they call it bull **** when you lie in Texas.
Race Director
Joined: Nov 2002
Posts: 12,142
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From: Taylor Michigan
Originally Posted by Little Mouse
I have been living in Texas for a long time now so I lie all the
time, oh I forgot they call it bull **** when you lie in Texas.
time, oh I forgot they call it bull **** when you lie in Texas.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Originally Posted by mvftw
I'm preforming my first leakdown test. A little background. I'm going through 1 qt. per hour . 3 plugs are oil soaked (2,4,& 8). I started with #8 and had 50% leak and when I moved the piston a little it dropped to 30% still bad. My question is how loud is the air I'm listening for? Even at 50% the leak didn't sound noticeable anywhere. At the carb, the tailpipe or the oil cap. Also this test will Not tell if the intake manifold is the problem (I already re-gasketed it). I'm sure the rings are bad, but I just ant to be sure.
... OR ... top/2nd rings installed upside down ... it does happen ... and they'll pump oil like crazy if installed upside down. Dunno how long you've had the problem ... but upside down rings tend to show up right away (pumping oil).