67 PCV Valve

[Nick Vigorito]

I have a simple, probably stupid question but I have gotten my 67 back together and noticed that I had a pretty significant ticking sound coming from the engine. Thought it might be the lifters but it is actually coming from the PCV Valve. I can feel it too. I never noticed this before but that doesn't mean it hasn't always been there. Is this normal or does it need to be replaced?

Thanks!

Nick Vigorito

[Joe L.]

Re: 67 PCV Valve

Nick------

It may be due to lower than normal vacuum caused by a number of things. If you have a 427 engine and are using an AC-CV-736C valve (GM #6423695), try using an AC CV-746C valve (GM #6484525).

[Gene M.]

Re: 67 PCV Valve

Nick, The ball inside the valve should be "free". The suction from the carb along with internal crank case pressure causes the ball to freely go open and shut causing the noise. It sounds as if it is working correctly. Check the stamped numbers on the valve to be sure it is the correct part.

[Nick Vigorito]

Re: 67 PCV Valve

Thanks, I will check the part number. I have a 327/350 engine. I thought this may be normal but was not sure.

[Iron Duke NCRS #22045]

Re: 67 PCV Valve

A similar post and discussion came up about a week ago. The probable problem is that there is not enough idle vacuum to keep the valve fully pulled in at idle so it dithers. Could be the wrong valve or a defective valve. Are you still running the correct "151" cam? If not the cam you have may not be producing as much idle vacuum as the original. It's tough to find a valve with the correct geometry but different vacuum characteristics because engineering data on PCV valves is tough to find. One way to produce more idle vacuum is to raise the idle speed.

Duke

[Nick Vigorito]

Re: 67 PCV Valve

Duke,

Sounds like the bottom line on this is that I should NOT be hearing this ticking sound from the PCV valve. I had the engine rebuilt about a year ago and the person who did it got the correct GM cam. Don't know anything about "151" but I assume that's it. My engine normally idles at about 750-800 rpm which is about where it is supposed to be. I guess it may be possible also that I have a vacuum leak somewhere, otherwise I probably have an incorrect or bad PCV valve. Thanks!

Nick

[Iron Duke NCRS #22045]

Re: 67 PCV Valve

Nick - My '93 vintage AC Delco catalog shows the PV736C PCV valve as applicable to all '67 Corvette engines, big block and small block. You might try a new one to see what happens. It's possibly some sort of tolerance build up, but it might also be a "designed in feature", like the dithering vacuum advnce unit in my '63 Special High Performance engine. They fixed it about mid-'64, so your SHP should be okay on that account. You might check with the engine builder to verify the cam. OEM is 3863151. It's an excellent all around high performance street cam for a 327. I'm pretty sure GM still sells it, and Federal Mogul makes an exact replacement, so availability is not a problem. I'm going to go back up the thread and ask Joe the difference between the PV736C and the other valve he suggested.

Duke

[Iron Duke NCRS #22045]

Joe - What's the difference...

between the 736 and 746 valves. Do you have any flow/pressure drop data?

Duke

[Dale Pearman]

CALL THE BOMB SQUAD

Ticking is usually associated with clocks or other time measuring devices used in conjunction with explosives to achieve various goals such as pay-backs, revolutions or other terrorist activities. Use caution!

Rev Varooom

[Joe L.]

Re: Joe - What's the difference...

Duke-----

No, I don't have any specifications for either valve. However, the CV-746 valve was the one designed for use with engines which might be expected to produce lower idle vacuum like the L-88/ZL-1 and the 70-72 LT-1.

[Joe L.]

Re: 67 PCV Valve

Duke-----

With respect to 1967 Corvettes, the CV-736C valve is applicable to 427s only. Apparently, Nick has a 327 cid engine. These engines require PCV valve AC CV-726C (GM #6422721). Unfortunately, this valve has been GM-discontinued for over 10 years.

[Kieran A.]

Re: 67 PCV Valve

Nick, I may have an NOS 726 pcv valve that I purchased years ago at a swap meet. I have since sold my 327/350 coupe. Let me know if you are in need of the valve and I will look for it. Regards, Kieran #11373

[Dale Pearman]

Vacuum

The 327 cu in 350 Hp "151" cam pulls pretty good vacuum. As I recall, it's ground on 112 degree lobe centers, 222 degrees on both lobes at 0.050 inch, and lifts 0.441 with 1.5 rockers. I personally don't like where the intake valve closes so I use this cam mechanically advanced 4 degrees. It sure as hell works in a 400 cu in mouse motor and if you want to put it in straight up in a 327 it'll run like a raped ape on the high end. I've NEVER lost a race with this cam!

Varooom!

P.S. If you need to pull stumps out of the ground use Rhodes lifters and an iron intake with an AFB.

[Dale Pearman]

Re: 67 PCV Valve

How about looking around to see if you purchased a 1962 PCV "729" at some point in the past. Joe won't let me have his!

Varooom!

[Nick Vigorito]

Re: 67 PCV Valve

Thanks, I will let you know!

Nick