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Sad News from Compression Tester

E

ezuskin

Contributing Member
"I decided I would perform a c

"I decided I would perform a compression test before sinking any money into manifolds and risers on my pair of 440s. All going OK until I got a 30psi reading on one of the cylinders. I ran the motor up to temp and up to 2500rpm to break any crud free if it was just a sticky valve. I also put oil into cylinder to see if that would temporarily seal a bad ring. Only got up to 45psi with oil, then back to 30psi after running motor. Lots of blow by from rocker cover also. Engine runs OK but a bit smokey from exhaust and rocker cover. Any words of encouragement would be appreciated.
Eddie Zuskin"
 
"A compression leak down test

"A compression leak down test can help you isolate
an intake,or exhaust valve leak or piston blowby.
A couple things it may be are. Stuck open valve,Burnt valve, head gasket, not likly piston or ring damage. As I reread your statement.
I would pull valve cover. look for broken valve spring. If not time to pull cyl head and inspect"
 
"David,
Thanks for taking tim

"David,
Thanks for taking time to reply. I am willing to perform leakdown, then pull valve cover or even pull intake and cylinder head. That's about the limit of my engine building skills. I replaced the heads(one was cracked from blown headgasket) on a small block GM mercruiser, and twice on a 4cyl DOHC Lotus motor. So I am not in "Panic Mode" until those skills are exhausted.

Why "not likely piston or ring damage?" Would pieces of metal be making noises?
Regards,
Eddie"
 
"Bad rings would be my guess s

"Bad rings would be my guess since the oil raised the compression a bit, then it went away.

Jeff"
 
"30 psi+ oil= I would expe

"30 psi+ oil= I would expect to see 80 to 130 psi.
Unless damaged piston? less likely.
My thought. blow by one rocker cover?= Compression up the valve stem of the open,bent,or burnt valve.
Let us know
Thanks"
 
"It's a valve. The compres

"It's a valve. The compression would have gone way up with the oil you added if it was a ring. The head is very easy to get off, pull both and take them to your local machine shop."
 
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