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post #1 of (permalink) Old 12-03-2006, 09:38 PM Thread Starter
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Oil filler blow back

I have a problem with my 304, at idle it has a bit of oil vapor coming out of the breather cap. at about 2K RPMs it is as if the engine is on fire. The intake manifold is soaked in oil.
I replaced the PCV valve today and that didnt help.

It is running a little rich but its not that bad.

Any sugestions why this is happening?
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post #2 of (permalink) Old 12-03-2006, 10:05 PM
 
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Re: Oil filler blow back

It sounds like blowby. When cylinder rings on a motor are worn then excessive amounts of combustion gases (all engines have a small amount of gas that gets past the rings) escape the combustion chambers, past the rings, into the crankcase. The PCV system is designed to neutralize any pressure in the crankcase, and circulate filtered air through the crankcase, so combustion gases don't build up. If the Engine is old, and the rings are bad, or if the PCV system is not functioning correctly, then you can get excessive blowby out of oil filler caps, or any other openings in the engine.
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post #3 of (permalink) Old 12-03-2006, 10:14 PM Thread Starter
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Re: Oil filler blow back

Any way of checking rings other than pulling it all apart? would the cylinder presure be lower in a cylinder with bad rings?
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post #4 of (permalink) Old 12-03-2006, 11:50 PM
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Re: Oil filler blow back

You can do a Leak Down Test. It's about the best indicator test you can do without tear down.
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post #5 of (permalink) Old 12-04-2006, 12:22 AM
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Re: Oil filler blow back

For a few bucks try Restore . It worked great for me on two worn 258s. Of course, if you have a cracked ring or worse it will not help.
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post #6 of (permalink) Old 12-04-2006, 01:31 AM
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Re: Oil filler blow back

Check the PCV valve. But if you are getting tons of vapor at idle or clouds at 2000 RPM (no load), especially if the engine is still cold, than I would suspect a hole or crack in a piston. As LEVE said do a compression test to tell for sure.
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post #7 of (permalink) Old 12-04-2006, 05:12 AM
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Re: Oil filler blow back

another little test is to check the compression of each cylinder.. they should all be in the same range.. if you have cylinders with low compression.. squirt in some oil.. then check the compression again.. if it rises.. then the rings in that cylinder are worn... if it doesnt.. then you have more serious problems..
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post #8 of (permalink) Old 12-04-2006, 12:18 PM
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Re: Oil filler blow back

Make sure you have vacuum to the PCV valve. It sounds strange but I had that problem with my 78 dodge. The carb had so much carbon in the pcv port, there was no vacuum. I hand turned a drill bit to remove the carbon and it worked again.
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post #9 of (permalink) Old 12-04-2006, 04:24 PM
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Re: Oil filler blow back

[ QUOTE ]
Make sure you have vacuum to the PCV valve. It sounds strange but I had that problem with my 78 dodge. The carb had so much carbon in the pcv port, there was no vacuum. I hand turned a drill bit to remove the carbon and it worked again.

[/ QUOTE ]

Ditto that! My vac port (on the adapter under the 2100) was caked/clogged/crusted to the point I had to use a cordless drill to spin the bit! [img]/ubbthreads/images/graemlins/blush.gif[/img]
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post #10 of (permalink) Old 12-04-2006, 06:09 PM
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Re: Oil filler blow back

[ QUOTE ]
The intake manifold is soaked in oil.
Any sugestions why this is happening?

[/ QUOTE ]


That's normal, just keep driving it..........
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