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post #1 of 6 (permalink) Old Jul 6th, 00, 04:39 PM Thread Starter
Join Date: Jul 1999
Location: Rising Sun, MD
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About a week ago the 350 in my 69 started to blow blue smoke. I took out the spark plugs and the plug in cylinder 3 was fouled with oil... badly. This was the only cylinder like this. Did a compression test and all were consistant, even cylinder 3. Any suggestion on what may cause this?
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post #2 of 6 (permalink) Old Jul 6th, 00, 04:56 PM
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My first thought is a bad valve guide or a seal on that number three cylinder. If it were a bad ring on the #3 cylinder, it would probably would smoke ALL the time.

You should do the compression check with the engine hot because it makes the oil thinner and the problem will show up more readily than if the engine is tested cold.

You could remove the spark plug and squirt some oil down into the cylinder and if the compression jumps up on #3 then more than likey it is a piston ring problem instead of a head related problem.

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post #3 of 6 (permalink) Old Jul 6th, 00, 05:02 PM
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Sounds to me like a valve stem seal or worn guide. If the compression test shows #3 is holding pressure, then the valve and seat should still be good. You're probably just sucking oil in past the intake valve stem/guide. Minor repair once the head's off but I'M not aware of anyway to repair it while still installed on the engine. If anyone knows a way I'm sure we'd BOTH like to know about it.

Does it continuously blow the blue smoke, or does it only happen on initial start-up then go away?
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post #4 of 6 (permalink) Old Jul 6th, 00, 05:08 PM
David Pozzi
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I can think of a couple.
Most likely it's an intake valve seal. Which is usually a rubber O ring between the intake valve stem and the retainer. Sometimes they can break and fall out.

Some times a loose piece of valve cover gasket can plug a drain back hole and flood the valve area with oil. But this usually causes oil fouling at the rear of the engine as that is the low end of the engine.

The rings or ring lands can break, If it's a ring land it might not show up on a compression test.

The intake manifold can leak oil from the valley area into the port. This would be accompanied by a miss and spitting back while idling.

If a wrist pin came loose it might contact the cylinder wall and put a groove in it leaking oil, but compression would be down too.

Most likely it's the valve seal. If you have the type that goes over the valve guide, it could be worn out.

Either way, you can put air into the spark plug hole and change the seal and add a push on seal over the valve guide. The intake side is the one to worry about.

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post #5 of 6 (permalink) Old Jul 7th, 00, 03:31 PM
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Join Date: Aug 1999
Location: Ontario, Canada
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Same thing happened to a friend of mine with his Corvette, It was his aluminum Intake that was bad, The one cylinder always fouled up on his recent rebuild, It was one of the inside cylinders. It was sucking an oil mist from from the lifter valley, it was most noticable when he backed off the throttle.He went through all of the trial and error replaced heads, rings etc. only to have the same problem , replaced the intake and no more cloud of blue.
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post #6 of 6 (permalink) Old Jul 7th, 00, 08:41 PM
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Like they said check the intake.A friend of mines 454 chevelle started that.When I started to take the intake off,I noticed the bolts were very very loose.Turns out he didnt tighten them good because he didnt want to scar up his factory aluminum intake.Plus he had cheap rebuilder gaskets.FelPro gaskets and good tightening fixed it.Its a good a guess as any.Good luck.
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