Vented valve cover or no?

[tbucketnut]

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

[AZKen]

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)

[LEWISMATKIN]

and under each valve cover is a pcv valve screwed into an intake runner in the cylinder head.

[tbucketnut]

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

Thanks,
Steve

[AZKen]

Yes, they SHOULD be removed and cleaned with carb cleaner.

[tbucketnut]

Thank you Ken, much appreciated.

[AZKen]

Glad to help.

[LEWISMATKIN]

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.

[jbgroby]

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?

[AZKen]

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.

[Quigley]

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?

On your 60 you should have a vented cap and a tube on the rear that goes all the way down and vents by the pan. My 62 is like that. I don't know what year they changed them but I know my 66 has the PCV valves,closed caps on the valve covers and just a vented can with filter on the rear motor..I like the old style better..I'm pretty sure yours is correct for a 60. Dave

[LEWISMATKIN]

Jake, the 1960 model had the road draft system. It was in 63 that the pcv system was introduced.

[FetchMeAPepsi]

I can confirm that 62 had the road draft system. Or as I like to call it, the "cut your head open any time you work under the truck system".
:P

[jmfurgason]

No PCV on heads of my 1963 305E just filter behind driver side crankcase, is this standard ??

[Quigley]

If you have the filter in the Rear of the motor it should have a PCV valve under each valve cover,screwed it the heads by the rocker arms. Dave

[LEWISMATKIN]

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? Jake, the road draft is correct for your engine, given the fact you have the road draft breather. Don't seal up your valve covers with non-vented caps, that is how your engine breathes. Simply clean the caps, and lightly re-oil them.

[tbucketnut]

On my 64 305E, I had to reinstall the valve cover breather because I get too many crankcase vapors and it has caused a leak at the valve cover above the starter. I firmly believe this is because my valve guides are worn causing combustion gases to enter under the valve cover, could also be the reason I have a couple lower compression readings in two of the cylinders. I plan on doing a leak down test to confirm. I haven't studied the GMC pcv system yet but if like other systems it is a controlled vacuum leak into the intake runner that is sucking out unburned crankcase vapors. It has a specific orifice to control a specific amount of flow, beyond that, will remain crankcase vapors that can pressurize the crankcase causing leaks like the one in my valve cover. I have heard people having rear main leaks and gone through expensive repairs to replace the rear main only to have the new one leak too, this could because of a broken ring or worn valve guide or seal too.

Also, I see some of the 305 engine series had road draft tubes/ vented valve cover caps, others after 1962, had pcv systems with the filter canister in place where the road draft tube usually resides and non vented valve cover cap and pcvs screwed into each cylinder head's intake port. My truck was made in Oakland Calf. and was probably one of the ones with calf. emissions requiring it to have the pcvs. Haven't looked into the WW carburetor yet to see if jetting was different because of this but suspect there were jetting changes too.