1964 PCV valve location

[Timothy B.]

Re: 1964 PCV valve location

GM must have had the same problem getting the pcv correct as they did with the vacuum advance in 1963.

Can someone explain to me what happens when the flow changes in the closed pcv system and the air flow through the carburetor creates more suction than manifold vacuum thus the system reverses. Does the pcv close or stay open to allow air to enter the engine.

[Michael H.]

Re: 1964 PCV valve location

I believe that the pn is 3846107 (which replaced 3846109 in 9/5/63)
It is shown in 64AIM, Sec6 sheetC3.00 as # 14.
Then again in SecL76 sheet1.00/3.00 with no part number, but in SecL84 sheet5.00 it is marked as "Prod Connector" I show it referenced to Gr 8.963 which I do not have.

[Duke W.]

Re: 1964 PCV valve location

The option sections only include parts specific to that option. If an illustrated or named part is listed as "production" or something similar, it is the same part as used with base equipment, which is this case is the 250 HP engine, and that part number should be listed in the base engine section of the AIM.

PCV systems on carbureted engines must have some sort of anti- backflow device or flame arrestor to prevent a backfire from propagating into the crankcase, which can cause an explosion.

PCV valves "close" if reverse flow is encountered thus protecting the crankcase. The '64-'65 PCV systems without valves incorporate screens to arrest flame propagation. In "normal" flow direction the restrictor limits flow at high manifold vacuum. At WOT the can flow "backwards", and the screen in the air cleaner base is the flame arrestor. Port injection engines are less suseptible to backfire caused crankcase explosions because the manifold and plenun are not wet with fuel as in a carburetor/manifold system, so backfires won't propagate to the crankcase even without a screen or anti-backflow valve.

Back in the early 2000s I put in a lengthly post explaining the purpose and various design architectures/considerations of PCV systems. It can be found with a search. Also, an edited version was published in The Corvette Restorer.

Duke

[Michael H.]

Re: 1964 PCV valve location

Alan,

In the 1964 AIM (SECT 6, SHEET C3.00)
GM # 3846107 is the part number for the hose (#14 in "box").
GM # 3853720 (#13 in "box") is the part number for the connector which before 9-5-63 was 3846109 according to the revision record.

Dave

[Alan D.]

Re: 1964 PCV valve location

Here is the L84/FI fitting - sorry for poor picture however one can see what Michael is talking about. Note remains of Cad type finish, additionally a large "P" is stamped on both my original parts. The Paragon picture shows a clearer general view. (did correct my last post to correct pn)

[David L.]

Re: 1964 PCV valve location

Michael,

A normal 1/4"-18 NPT brass elbow has a tube for a 3/8" hose (R/S in photo). The I.D. measures almost 5/16".

The 3853720 elbow must have 1/4" NPT-18 with a tube for a 3/8" hose but the I.D. must be much smaller as you stated. I assume the original 3853720 elbows were steel as the Paragon reproduction appears to be steel.

I found this unidentified 3/8" NPT-18 brass elbow (w/Weatherhead logo) with tube for a 5/16" hose in my collection (L/S in photo). The I.D. measures about 7/32".

Dave

[Michael H.]

Re: 1964 PCV valve location

Here is the L84/FI fitting - sorry for poor picture however one can see what Michael is talking about. Note remains of Cad type finish, additionally a large "P" is stamped on both my original parts. The Paragon picture shows a clearer general view. (did correct my last post to correct pn)

Thanks Alan. The pic clearly shows how small the actual orifice is. MUCH smaller than a typical fitting of the same configuration.

[Jeff B.]

Re: 1964 PCV valve location

David,
The fitting that screws into the back of the carb is actually two pieces. There is an adapter nipple that is male/female that screws in first and then the elbow which has the metered hole. CC sells both parts and I think they are HP specific but I'm not sure. It is essentially a controlled vacuum leak that pulls crankcase air and mixes it with normal combustion air. Air is let into the crankcase via the breather tube that connects to the screened opening inside the air cleaner so the air is filtered. If you don't get correct orifice you will not get the engine to idle down to the factory spec. The carb idle circuit accounts for this air intake and when you adjust the idle mixture screws you altering the fuel that is mixed with the combined air supply being drawn in through the primary butterfly valves as well as as the PCV system. The rest of the carb including the shaft bushings have to be in good shape or the resulting vacuum leaks combined with the controlled leak of the PCV will create a higher than normal and inconsistent idle speed.

[Timothy B.]

Re: 1964 PCV valve location

Jeff,

Also adding to that mix you mentioned is the choke hot air tube. I have measured the brass restriction where the choke housing attaches at .098" so it's as big as the pcv restriction, lots of air leak here also.

That's why I am now questioning the size of the tube through the exhaust manifold as some have reported a much reduced (pinched ) tube on earlier engines.

[Michael H.]

Re: 1964 PCV valve location

Jeff,

Also adding to that mix you mentioned is the choke hot air tube. I have measured the brass restriction where the choke housing attaches at .098" so it's as big as the pcv restriction, lots of air leak here also.

That's why I am now questioning the size of the tube through the exhaust manifold as some have reported a much reduced (pinched ) tube on earlier engines.

Carburetors are correctly calibrated to compensate for the metered orificas.

[John D.]

Re: 1964 PCV valve location

Michael Hanson, I read all your posts and see that the gang here may have missed what you were talking about. The original question was about a PCV valve in a 64 wasn't it? Then the topic went to a restrictor fitting.

Now If i missed the subject that I apoligize but what Michael was referring to is the early 64 FI cars used a PCV valve AC 590 (not 590C). Early means from the start of production up to maybe early Dec 63. In Nov and Dec 63 we believe that St. Louis and RP were installing two different model FI's at the same time. Left over 63 FI's 7017375 R and the newer 7017380 units.
Yes the 64 Aims is weak in certain areas and this is one of them.
As mentioned the same restrictor fitting was used on carbs and 7017380 plenums. The original fittings had various logos on them that the repros lack.
GMGMGM or P or P with a circle around it are the 3 logos I have seen.
Recently I got another 64 to restore and when I took the hose off/from the restrictor fitting I laughed a little as someone had a fitting installed with a huge hole and no restriction. Bet that FI ran like crap. JD

[John H.]

Re: 1964 PCV valve location

The special 90* fitting that screws into the driver's side of the Holley 2818 on the '64-'65 L-76 (327/365hp) and the '65 L-79 350hp engine has an .090" orifice.

[Michael H.]

Re: 1964 PCV valve location

Michael Hanson, I read all your posts and see that the gang here may have missed what you were talking about. The original question was about a PCV valve in a 64 wasn't it? Then the topic went to a restrictor fitting.

Now If i missed the subject that I apoligize but what Michael was referring to is the early 64 FI cars used a PCV valve AC 590 (not 590C). . JD

Bingo !! You got it JD. Gold star for you today. I was wondering how long that was going to take. Thought Duke would figure it out first but he sounded pretty sure no such thing existed.

Yes, early 64 with the recalibrated 63 FI unit, 7017375R, used most of the 63 components, including the entire 63 design crankcase ventilation system.

[Stuart F.]

Re: 1964 PCV valve location

Michael;

Are you sure you're not awarding old Chrysler Penta stars? That's the first thing I thought of when I saw it b4 reading the text.

FWIW, Tim and I had a thing going about the draw through the hot air tube a while back when I was deciding as to whether it was a factor or not in determining my idle mixture concerns before changing to an electric choke. I measured an insignificant amount and assumed the tube on my 63 was like the old pinched tubes found on many 57 era Chevy V8's. Much to my chagrin, many jumped on me for that. As it turned out on my application, as I suspected, it was a non-factor. I had been searching for an AFB housing with the connection on the side instead of the cover. Finally gave up and decided I didn't need any more hot air in the mixture here in Florida.

Stu Fox

[Michael H.]

Re: 1964 PCV valve location

Michael;

Are you sure you're not awarding old Chrysler Penta stars? That's the first thing I thought of when I saw it b4 reading the text.

FWIW, Tim and I had a thing going about the draw through the hot air tube a while back when I was deciding as to whether it was a factor or not in determining my idle mixture concerns before changing to an electric choke. I measured an insignificant amount and assumed the tube on my 63 was like the old pinched tubes found on many 57 era Chevy V8's. Much to my chagrin, many jumped on me for that. As it turned out on my application, as I suspected, it was a non-factor. I had been searching for an AFB housing with the connection on the side instead of the cover. Finally gave up and decided I didn't need any more hot air in the mixture here in Florida.

Stu Fox

Stu,

Yes, I thought JD deserved the Chrysler star.

I think the hot air tube flow is much less than the orifice in the choke so, even though it looks restrictive, it probably isn't.
I agree on the "no more hot air" needed, especially here in our Floriduh heat.

By the way, have you had a chance to try the ethanol free fuel?