Low compression in first cyl - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jrat · 05-30-2002, 08:14 PM

Im going to go check out this truck tommorow,what should I know about this low compression issue. Sorry im a tech idiot.
Is it somthing to be really concerned about? rings ? head? valves ?

72 GMC PU, <3/4>T, 350 4bbl, V8, reblt eng, 100,000 orig mi, orig owner, maint, new pts installed, have all rcpts for past 4 yrs, runs gd, low compression in first cyl

Longhorn Al · 05-30-2002, 09:44 PM

My uncle and I found out one of my cylinders was missing. We took out that plug and hooked up a pressure guage. It was only putting out around 58psi.

He squirted some oil (not motor oil) into the cylinder. He said that if the pressure goes back up to normal, then it's the rings. If it stays the same, then it's the valves. Well, mine stayed the same. So I guess I just need a valve job. At least I don't have to tear apart the motor and replace rings!

The cylinder misses around idle, but it starts firing when I pick up speed and the compression builds.

texnician01 · 05-31-2002, 12:11 PM

yes you are correct. if you squirt oil into the cylinder and the compression does not get better then it is the valves. you can use any kind of oil, heck even tranny fluid will work. I would use something like a straight 30wt oil so it is good and thick.

Nathan

05-30-2002, 08:14 PM	#1
jrat Registered User Join Date: May 2002 Location: North Vancouver Canada Posts: 5	Low compression in first cyl Im going to go check out this truck tommorow,what should I know about this low compression issue. Sorry im a tech idiot. Is it somthing to be really concerned about? rings ? head? valves ? 72 GMC PU, <3/4>T, 350 4bbl, V8, reblt eng, 100,000 orig mi, orig owner, maint, new pts installed, have all rcpts for past 4 yrs, runs gd, low compression in first cyl

05-30-2002, 09:44 PM	#2
Longhorn Al Texas Longhorn For Life Join Date: Jun 2000 Location: Austin, Texas Posts: 698	My uncle and I found out one of my cylinders was missing. We took out that plug and hooked up a pressure guage. It was only putting out around 58psi. He squirted some oil (not motor oil) into the cylinder. He said that if the pressure goes back up to normal, then it's the rings. If it stays the same, then it's the valves. Well, mine stayed the same. So I guess I just need a valve job. At least I don't have to tear apart the motor and replace rings! The cylinder misses around idle, but it starts firing when I pick up speed and the compression builds. __________________ 1970 C-10 named HOSS 400SB/TH350, PS, PB, 3.07 gears \m/ Hook 'Em from Austin, TEXAS

05-31-2002, 12:11 PM	#3
texnician01 Senior Member Join Date: Mar 2002 Location: 12 Miles South of Des Moines, Iowa Posts: 359	yes you are correct. if you squirt oil into the cylinder and the compression does not get better then it is the valves. you can use any kind of oil, heck even tranny fluid will work. I would use something like a straight 30wt oil so it is good and thick. Nathan __________________ 69 C-10, 340HP 327 55 chevy 4 door 150 47 Willys CJ-2A 05 Harley Night Train 06 1200 Sportster (Wife's bike) 70 Honda CL350 OIF2 & OIF7 Veteran Nathan & Tiffany



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.