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Old 11-16-2005, 07:54 AM
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technical talk about blowby.

After having read many posts and articles concerning oil consuming problem I am still not fully understanding how and why this happens.

Worned out valve seals,valve guides,oil rings can eventually let oil reaches the combustion chambers where the actual oil gets burned under the extreme hot ambient..this I got it.

Where Its not so clear anymore is when the word "blowby" is used....my understanding of blowby is the compression ring (s) is not achieving a sufficient seal with the cylinder wall and because of this some of the pressure created from the mixture explosion will makes it way to the crankcase the other side of the piston.....hence am I right to think the only consequence of blowby (if not compensated through a crankcase ventilation system)should be oil trying to find its way out of the motor through wherever it can,the easiest being the valve covers breather(s) and eventually through the many different seals? I ask this as I think there are sometimes references linking a blowby situation responsible to oil burning ...does this stand true and if so how does it happens?

Typical question and answer illustrating this would be: " My fresh engine burns oil how this can happen?" Answer: " Your rings haven seated yet and you have some blowby situation...this should correct with time"....shouldn't the right answer to this question be: Your oil rings not having seated yet let oil reach the combustion chambers where it gets burned .

Another question raising from my understanding of blowby is can it be that a larger oil volume accumulates under the valve covers and the valves stems/seals get submerged under oil hence a much greater possibility of oil making its way to the combustion chambers?? In spite of otherwise good normal condition of the said valve seals or guides? In such a case I agree that blowby is causing oil to get burned. Also for the same possible larger that normal oil volume under the valve covers can we picture a PCV valve having almost its tip so close to actual solid oil level that oil will get sucked in,overcoming the oil baffle capacity, towards the vacuum source (the carb vacuum port) and will get burned in the combustion chambers again??

Trying to better understand the "how and why" here..thanks for your attention and help.
Ronald.

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Old 11-16-2005, 08:01 AM
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You understand correctly.

Blowby is just the rings allowing cylinder pressure to escape. This reduces power by reducing the cylinder pressure exerting a force on the piston. It also reduces power by reducing the amount of trapped A\F on the compression stroke.

Oil can accumulate in the head becuase of the upward moving gasses keep the oil from returning the the pan.

Last edited by johnsongrass1; 11-16-2005 at 08:03 AM. Reason: insanity
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Old 11-16-2005, 08:31 AM
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why do we need pvc valves couldn't we just put a breather on it to vent the fumes or what ever needs vented? it kinda seems stupid to me to have oil fumes and stuff from the valve cover in the vacuum system to get burned?
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Old 11-16-2005, 08:54 AM
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That's true, But it's a emmision device. Raw unburned gasses called Hydrocarbons, some believe are destrying our own protective ozone layer. Many moons ago cars didn't have 'em. Some even had road draft tubes so that the wind flowing under the car sucked out unwanted fumes and the like. Can you imagine beign behind that guy with a bad set of rings?

A (P)ositive (C)rankcase (V)entilation system burns up unused hydrocarbons.
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Old 11-17-2005, 10:30 AM
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so it wouldn't be illegal for me to take off my pcv valve because i'm having trouble with the angle it is at with the new intake manifold i have and it'd be easier to just vent it to the air
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Old 11-17-2005, 10:34 AM
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It would be illegal..........easier to just change the angle by getting a PCV that fits properly.
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Old 11-17-2005, 01:06 PM
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Quote:
Originally Posted by poncho62
It would be illegal..........easier to just change the angle by getting a PCV that fits properly.
And you will not use as much oil either.

Part of the PCV system helps keep the crankcase under vacuum condiditons. That inturn helps the rings seal better. Make sure you a have sufficiently sized inlet for air into the crankcase.
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