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Joined: Nov 2001
Posts: 5,906 Likes: 8
Former ChatMaster ChatMaster - 5,000
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OP
Former ChatMaster ChatMaster - 5,000
Joined: Nov 2001
Posts: 5,906 Likes: 8 |
In the past I've always tested my pcv valves by blowing in both ends. One way will allow air to "freely" flow, and the other will not allow ANY flow. In testing my 1966 Chev CV-726C, it freely flows from manifold to carburetor, and then "slightly" allows a flow in the reverse direction. Is this bad? I always thought that ANY reverse flow was bad... That it might even mess with the vacuum reading in the carb by allowing "back-flow" to occur. Thoughts? BTW, these silly things cost from $20 to $65. (There must be gold inside them.)  Bill B
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Joined: Jan 2002
Posts: 30,701 Likes: 141
ChatMaster - 25,000
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ChatMaster - 25,000
Joined: Jan 2002
Posts: 30,701 Likes: 141 |
Gene Schneider
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Joined: Nov 2001
Posts: 5,906 Likes: 8
Former ChatMaster ChatMaster - 5,000
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OP
Former ChatMaster ChatMaster - 5,000
Joined: Nov 2001
Posts: 5,906 Likes: 8 |
Oh, I already ordered it, but I was just wondering if my memory was correct that it shouldn't allow ANY flow in the reverse direction.
Bill Barker
Previous VCCA CHAT Administrator
(VCCA Member: 9802)
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Joined: Nov 2001
Posts: 29,863
Tech Advisor ChatMaster - 25,000
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Tech Advisor ChatMaster - 25,000
Joined: Nov 2001
Posts: 29,863 |
The Mangy Old Mutt
"If It's Not Junk.....It's Not Treasure!"
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Joined: May 2002
Posts: 6,149 Likes: 42
ChatMaster - 6,000
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ChatMaster - 6,000
Joined: May 2002
Posts: 6,149 Likes: 42 |
I thought PCV was (Positive Crankcase Ventilation) which is generally plugged into the rocker cover with a hose to intake manifold. This valve should not allow air flow from intake manifold to crankcase but a reasonable air flow from crankcase to manifold but not a high flow. If your valve is connected otherwise it is probably something else. Never did like a lot of the "anti pollution" garbage fitted to engines.
Tony
1938 1/2 ton Hope to drive it before I retire
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Joined: Nov 2001
Posts: 5,906 Likes: 8
Former ChatMaster ChatMaster - 5,000
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OP
Former ChatMaster ChatMaster - 5,000
Joined: Nov 2001
Posts: 5,906 Likes: 8 |
Received my new (~50 year-old) NOS PCV valve today. As I suspected, the air blows FREELY in one direction, and is TOTALLY BLOCKED in the other.
So my old PCV, even after soaking in solvent overnight, and using Carb cleaner is officially BAD. It allows a small amount to flow in the reverse direction. I suspect that the ball inside is corroded after 51 years of use. Something for the trash barrel.
Bill B
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Joined: Dec 2016
Posts: 656 Likes: 3
Oil Can Mechanic
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Oil Can Mechanic
Joined: Dec 2016
Posts: 656 Likes: 3 |
The whole purpose of a valve is to prevent a crankcase explosion in the event of a backfire. Under this condition, it should slam shut.
In normal operation, a PCV valve only limits flow, and a simple orifice would work fine. Some cars are built with only an orifice (I have seen it but I cant remember what).
It probably would have been just fine since you cleaned it out, and may have even shut all the way with the sudden rise in pressure in the unlikely event of a backfire.
I guess its ok now anyway, now that you have a known good one. :)
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