Technical Vacuum port?

GMC302
Is this a vacuum port? Where do I run the line and what size is that fitting?

 

No, its to scavenge fumes from the underneath the rocker cover. Depending on the year it went to the PCV canister or intake port

 

If that is the valve cover, a pcv valve would connect to that and then manifold vacuum. Never seen an AN fitting used for pcv before.

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You can see by the raised portion of the rocker cover under the fitting it was a stock fitting. I have 2 of them like this. The embossment of the script GMC logo shows it is an early cover prior to the PCV systems. I believe it to be military for a sealed engine and could have gone to the air cleaner system but i am not sure never seeing one in a GMC duece -1/2.
I could easily be used as a PCV system for you today if you can find a PCV valve with threads to screw into a carb base.
Most covers with the earlier GMC in an oval had 2 "slit" breathers and an oil fill cap at the front. The crankcase had its own breather on the right side.
The last GMC's manufactured in the early to mid 60's would have had the PVC provisions but not the early cover.

 

So can I go into the side of the carburetor where that rubber plug is or do I need to go into the intake

 

That engine must be a military 302 cube inline 6 , that fitting was used to seal the engine to the intake so the truck could run under or in very high water !!!

 

Yes; that's why I painted it that color in honor of it being ex military.

 

Ok another option-just put a plug in the hole and not worry it about anymore?

 

So what is the size of the vacuum hole in the Clifford intake ?


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If it were me I would put a line on it to the underside of the air cleaner. It will help with under hood smell and vapor.
I'm glad to see the proper water line from the rear off the head to the thermostat housing. You can do them lower but a necessary line for proper cooling especially with higher compression.

 

You could use an in line pcv, then connect to the intake. Otherwise you will have a big vacuum leak. Running to the air filter base without a pcv would also work. Either way it vents the crankcase.

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Anybody know? So I now understand that I should run it either to the air filter or intake instead of capping it off.

 

Why can't you measure what size it is ?

 

I'm not smart enough to know what was there before but generally speaking, never block off outside vents or "road draft" tubes or anything like that or there will be trouble. Find out how it was plumbed and do exactly that, may be some parts missing after all these years, removed by some dumb shit.

 

Oh crap, I misspoke. I didnt mean PVC. Although that is an option. The second option is that it went to the road draft tube to scavenge fumes. sorry. I am a dope sometimes/

 

Ok does anyone have a part # for a pcv valve that will work with the GMC302?
In that one picture it shows my carb with a rubber plug, on the drivers side.That port is for "pcv" so I will plan to connect there.

 

V112 Standard is a GM inline pcv valve. Works in a lot of situations like this.

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Thanks Greybeard

 

That is one fine looking engine. Very nice.

 

I'd find one for a 62 Chev 235. The Calif cars would have one. They would have been screwed into the base of the carb or a space under it and be an AC. The hose side might hve connected to the old road draft tube spot or a connection on the rocker cover I don't remember.

 

Updated picture with new lines

 

Nice...