27 psi compression test
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Joined: Jul 2006
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From: Burt, Iowa
27 psi compression test
Hi everyone. Ive been having trouble with my truck the last 500 miles or so. Its a 1979 400 2bbl with a little over 100k on her. Lately it has had blue smoke out the exhaust. When I first start it up it smokes a little, but when shes warmed up she smokes alot. When I pulled the plug for #8 it was oil fouled shut,carbend up. By far the worst plug Ive ever seen. I did a compression test on all the cylinders and all but 2 where 135-138psi. I checked them all twice. The second lowest cylinder#5 was 121 both tests. The lowest one, #8 was 27 both tests,but on the second test I shot some oil in the cylinder and it still came out the same. Is it the valves ar rings? Thank you all, any questions please ask.
Thanks Chris
Thanks Chris
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Joined: Apr 2005
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From: Whitehorse Yukon
Is the mileage 100,000 miles or Km.
If you have 100,000 miles its time for a rebuild regardless of whether its a valve or rings. In a case such as your i would recommend a leak down test to confirm my diagnosis but from what you have said here it sounds like a valve since adding oil did not improme the compression pressure. I would pull the heads and see what you have. Most likely the guides are worn out . Check the top of the cylinder to see what sort of ridge you have.
Smoke on start up is valve seals and/or guides
When the cylinder has no compression the rings will not seat properly and will cause excess oil to enter that cylinder. A step by step tear down ,starting with the heads is in order.
What tim above said also is a good call and definetly worth the time takes to look . good call tim
If you have 100,000 miles its time for a rebuild regardless of whether its a valve or rings. In a case such as your i would recommend a leak down test to confirm my diagnosis but from what you have said here it sounds like a valve since adding oil did not improme the compression pressure. I would pull the heads and see what you have. Most likely the guides are worn out . Check the top of the cylinder to see what sort of ridge you have.
Smoke on start up is valve seals and/or guides
When the cylinder has no compression the rings will not seat properly and will cause excess oil to enter that cylinder. A step by step tear down ,starting with the heads is in order.
What tim above said also is a good call and definetly worth the time takes to look . good call tim
Last edited by Socketman; Aug 29, 2006 at 08:48 PM.
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New User
Joined: Jul 2006
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From: Burt, Iowa
Thanks. It has 100,00 miles. I did forget to mention that it still runs good but it has the occational pop out the exhaust also. Cleaned the plug and the pop goes away, so does most of the smoking. I will check the pushrod tommorow. I wont be able to pull the heads till the 10 or 11 of sept. Im in the process of getting the race car and trailer ready for the super nationals in Boone Iowa this next week. Thanks again Chris
Last edited by 350ford4x4; Aug 29, 2006 at 09:13 PM.
