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Old 01-04-2004, 03:01 PM
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Compression test results...

I just finished a compression test on my 1980 Silverado, sbc 350. As I stated before this truck was given to me but did not run well at all. I replaced the intake and carb with an Edelbrock 7101 and a 600 Holley carb. It still did not run well. I bought a compression tester today and here is the results:

#1 = 0 #2 = 158 #3 = 140 #4 = 148 #5 = 149 #6 = 157

#7 = 148 #9 = 155

I'm not much of a mechanic but I'm learning...how can I have 0 compression on #1 cylinder. I have set TDC before so I know the piston moves to the top and down. Can someone please suggest what problems I may have here. Any help is definately appreciated....thanks.

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Old 01-04-2004, 03:05 PM
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Toss some oil in hole#1 and see if the compression comes up, if it does, it's the rings, if it doesn't, it's the valves, or head gasket, or...?

Could be a flat cam too? In any case you have a dead hole.
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Old 01-04-2004, 03:09 PM
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Well that means you have a big leak in #1 cylinder ,more than likely you have a blown headgasket or a burnt valve,take that side valve cover off and have a look at the valve train,a leakdown test would pinpoint if you have access to air and the tools
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Old 01-04-2004, 03:13 PM
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Wouldnt you be more inclined to believe this is valve related? If it was the rings, wouldnt I have "some" compression? Could it be that one of the valves is not closing?
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Old 01-04-2004, 03:14 PM
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Yup
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Old 01-04-2004, 03:43 PM
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Re: Compression test results...

Quote:
Originally posted by tom_scott
I bought a compression tester today and here is the results:

#1 = 0 #2 = 158 #3 = 140 #4 = 148 #5 = 149 #6 = 157

#7 = 148 #9 = 155
You better check number nine again!

If the hose has a quick disconnect from the compression guage, take it off and remove the schrader valve from the end of it. You can now use the hose to charge the cylinder with compressed air. It's usually a "D" type fitting and is the most common quick diconnect fitting you'll find on air hoses.

Loosen the valves on the cylinder you want to check so that both valves are closed. Then shoot some air to it and see what it says.

If you hear air escaping from the tailpipe, you have a burned exhaust valve. If you hear it from the carb, intake valve. If you hear it coming from the carb, first make sure it's not actually coming up through the PCV making it sound like a problem with an intake valve. Pull the oil fill cap and listen there, air escaping here would indicate a burned/hole in the piston.
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Old 01-04-2004, 03:54 PM
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I just wanted to add that when I first got the truck, I changed the spark plugs first thing. All the plugs looked pretty good with the exception of #1. It was caked solid with carbon. Today, when I pulled the plug, it was a little wet and smelled of gas. Because of it being caked with carbon the first time, could this be caused by the exhaust valve not closing? I guess Im just tryig to pinpoint the problem before I have to the head....thanks for your imput everyone.

BstMech....thanks a lot. This was exactly the kind of information I needed. I will do this next on the truck. i really appreciate your help....Tom.

Last edited by tom_scott; 01-04-2004 at 03:54 PM.
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