Silvaire
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Silvaire
Well for one thing, if you got a low reading how would you determine the cause of it?
Compression: What's good and borderline?
- Thread starter VWGhiaBob
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Well for one thing, if you got a low reading how would you determine the cause of it?
It's a hydraulic pump type dyno using hydraulic pressure as the resistance.
iAlex
Filing Flight Plan
I've heard it said that the difference between a regular automotive style compression test and a differential compression test is about the same as a Doctor listening to your heart with a stethescope when compared to performing an EKG.
The auto compression test can tell you that something is wrong, but the differential test can tell you what is wrong.
The auto compression test can tell you that something is wrong, but the differential test can tell you what is wrong.
jesse
Touchdown! Greaser!
Some truth to that. Plus I have no interest in standing beside a spinning prop holding a compression test gauge in the middle of the winter on a freezing cold ramp trying to test each cylinder while cranking while will likely trash your battery before you got through six cylinders. All so that you can determine "something" is wrong but have no idea what to go do the proper test that would have been faster to do in the first place
The reason we do them like we do them on airplanes is because it's very fast to do it that way on an airplane and tells you the most information. You'd save no time, would just waste time, and it'd be rather dangerous doing the automotive method.
Checkout_my_Six
Touchdown! Greaser!
Bob....compression checks are fine, but, they are just an indicator of your cylinder's health. The value of leak down is an indicator....and I'd not value it for a pass/fail test. Once one knows where the leakage is....the follow on diagnostic is where the value lays.
You are much better served to get a $50 dental USB camera from e-bay or online and perform a borescope of your exhaust valves and seats. While you're in there have a look at the cylinder walls and piston head. Much more info is gained from inspecting the inside of each cylinder than trying to evaluate a number from a leakage test.
Mike Caban has a wonder website loaded with great info for Beechcraft owner's and has a nice write-up on this preventative inspection technique. Beech also has a nice SB03-3 addressing leak down and cylinder inspection. The SB lays out how to perform the compression check and what is the "minimum acceptable leakage" limit. This limit is determined using a "master orifice". For your large bore engine, depending on your gauge, readings as low as 40 psi can be perfectly acceptable.
He goes thru all that in this link.
Oh....and this is Rick....not Ben.
You are much better served to get a $50 dental USB camera from e-bay or online and perform a borescope of your exhaust valves and seats. While you're in there have a look at the cylinder walls and piston head. Much more info is gained from inspecting the inside of each cylinder than trying to evaluate a number from a leakage test.
Mike Caban has a wonder website loaded with great info for Beechcraft owner's and has a nice write-up on this preventative inspection technique. Beech also has a nice SB03-3 addressing leak down and cylinder inspection. The SB lays out how to perform the compression check and what is the "minimum acceptable leakage" limit. This limit is determined using a "master orifice". For your large bore engine, depending on your gauge, readings as low as 40 psi can be perfectly acceptable.
He goes thru all that in this link.
Oh....and this is Rick....not Ben.
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