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Old 07-04-2010, 06:15 AM
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oil in cylinder

I have a cylinder on my 383 that is fauling the plug. I've ran a compression test and a cylinder leak down test and I have 160 psi compression and I am holding 100% in the leak down test. This motor does not have more than 5000 mile on it. All the other cylinders are buring clean but #6. When you are on it hard and back off the throttle it will put out a puff of blue smoke. I just pull the spring and the valve seal (positive type) and it looks fine. I put a bore scope down the spark plug hole and the top of the piston is black from oil. I've always thought if it was rings the outer edge of the piston would be clean but the center would be black. And if its a valve seal or guide the center would be clean and the outer would be black. Well as far as I can see with the bore scope the whole piston is black. I chacked the valve guide (Dart Pro Alum 200 cc heads) were great.

This plug is not wet the black is hard and shinny.. you can not wipe it off.

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Old 07-04-2010, 07:07 AM
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compression test

if you got 160# in the problem cyl then the rings are fine and so is the valve seat.. i'd be looking at the valve guide and seal. do u have the oring or full seal..
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Old 07-04-2010, 11:36 AM
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could it be bad spark? how long has the plug been fouling? its definatly not your rings if its 160 with 0 leak. I would put an inline spark tester and check that, if its good, check your valve stem to guide clearence vs a good cylinder, while your in there change the seal.
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Old 07-04-2010, 04:47 PM
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Could also be intake gasket leak pulling oil from lifter valley, happens more common than you would think.

There is no credibility to you theory of where the carbon is on the piston and ring or valve seal leaks.
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Old 07-05-2010, 09:00 AM
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I have full seals. I pulled the springs and they look fine and are tight to the valve stem. The guides feel tight.

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Originally Posted by delawarebill
if you got 160# in the problem cyl then the rings are fine and so is the valve seat.. i'd be looking at the valve guide and seal. do u have the oring or full seal..
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Old 07-05-2010, 09:01 AM
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Intake gasket??? That could be.


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Originally Posted by ericnova72
Could also be intake gasket leak pulling oil from lifter valley, happens more common than you would think.

There is no credibility to you theory of where the carbon is on the piston and ring or valve seal leaks.
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Old 07-05-2010, 09:07 AM
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An oil ring failure could result in lots of oil consumption and not change the cranking compression or the leakdown.
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