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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old December 16th, 2019, 08:45 PM
tbucketnut tbucketnut is offline
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Default Vented valve cover or no?

On my 64 with a 305E engine, this is the non california engine so there is no pcv but there is a crankcase fresh air filter on the driver's rear of the engine and the cylinder heads have the air valves that suck the emissions into the combustion chambers. My engine had a breather cap on the passenger side valve cover and I can smell blow by gases. I'm thinking this needs to be a closed system correct? I replaced the breather cap with a non vented oil fill cap on it and will see how it goes. Any comments will be appreciated because I have never seen this type of emission system.
Steve
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1953 Chevrolet 3100
261 cu inch, SM420
Finished Cab off restoration

1964 GMC 1000
305 V6, SM 420
Restoration is now started, still looking for an oldsmobile style power steering pump
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  #2  
Old December 17th, 2019, 01:08 AM
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AZKen AZKen is offline
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Default Re: Vented valve cover or no?

Per our/your 6060GMCCLUB website. At top banner: Jolly's page/engine.....scroll down for explanation of crankcase venting. Answer is: no valve cover vent. Fresh air enters into the filter can, thru filter and etc. (on the filter can style motors)
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Old December 17th, 2019, 03:13 AM
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LEWISMATKIN LEWISMATKIN is offline
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Default Re: Vented valve cover or no?

and under each valve cover is a pcv valve screwed into an intake runner in the cylinder head.
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Old December 17th, 2019, 06:20 AM
tbucketnut tbucketnut is offline
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Default Re: Vented valve cover or no?

Good info, is there a replacement number for these pcvs? Or can they be removed and cleaned with solvent?

Thanks,
Steve
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Gig Harbor, Wa

1953 Chevrolet 3100
261 cu inch, SM420
Finished Cab off restoration

1964 GMC 1000
305 V6, SM 420
Restoration is now started, still looking for an oldsmobile style power steering pump
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Old December 17th, 2019, 07:18 PM
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Default Re: Vented valve cover or no?

Yes, they SHOULD be removed and cleaned with carb cleaner.
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Old December 17th, 2019, 11:20 PM
tbucketnut tbucketnut is offline
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Default Re: Vented valve cover or no?

Thank you Ken, much appreciated.
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Steve Stock
Gig Harbor, Wa

1953 Chevrolet 3100
261 cu inch, SM420
Finished Cab off restoration

1964 GMC 1000
305 V6, SM 420
Restoration is now started, still looking for an oldsmobile style power steering pump
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Old December 18th, 2019, 12:43 AM
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Default Re: Vented valve cover or no?

Glad to help.
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Old December 21st, 2019, 10:02 PM
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Default Re: Vented valve cover or no?

IF they don't clean up, the ac/delco p/n is cv623c. you may be able to pick up a pair of them on ebay.
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Old December 22nd, 2019, 03:03 PM
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Default Re: Vented valve cover or no?

On my '60 I too have a valve cover breather, but also have the filter tube behind the rdriver's side head. Do I need to remove the valve cover mushroom vented cap and put a closed cap too?
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Old December 22nd, 2019, 07:00 PM
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Default Re: Vented valve cover or no?

Don't think it makes any meaningful difference one way or another (to the motor). The Jolly page advertisement can be a guide or not. The can, in back, has it's own "intake". GMC called their system PCV. The advent of the vented valve cover was to release "crankcase pressures" said to cause oiling issues. So engineers decided to have it vent out thru there. They added baffling inside the "breather" to prevent oil from coming out. All kinds of set ups, pre smog/post smog.
Looks like stock for your motor is non vented covers.

Last edited by AZKen; December 22nd, 2019 at 09:26 PM.
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