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Username Post: blow by        (Topic#358811)
Posts: 73

Loc: Arizona
Reg: 03-13-09
11-14-19 09:41 AM - Post#2780144    

A month ago driving on the freeway about home my 74 truck with a 350 out if 98 Blazer in it had blown a quart of oil out the right valve cover. I ran a compression check and found all cylinders good. The other day after after driving the same route my PCV valve had blown out of the valve cover. It didn't blow the amount of oil as the first time but still. I thought blow by was only caused by bad rings and valves. If anyone knows any other reason give me a shout. The PVC valve is working as it should be and I pretty sure I'm working right too.


Member #271 Senior Chevytalk Moderator
Posts: 25311
Loc: Austin, TX 78748
Reg: 05-09-00
11-14-19 09:57 AM - Post#2780145    
    In response to badbob85037

Where is it routed to? Does the other side have an air inlet? Is it the same side oil is added?

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Posts: 73

Loc: Arizona
Reg: 03-13-09
12-13-19 12:10 AM - Post#2782045    
    In response to gchemist

The PCV valve is on the right side. It goes to the carb below the throttle on an Edelbrock 600. The left side is where oil is added with a 30/06 cartridge plugging the rear hole in the valve cover. It passed emission testing with no problem. Sorry it took so long to reply.

Posts: 45

Reg: 12-12-19
01-26-20 01:36 PM - Post#2785224    
    In response to badbob85037

Sounds like a bad PVC valve to me. For a few bucks, that is what I would try. They claim even if they rattle, they can still be defective. Plus, on the other side where you add oil, I would put in a breather. To much pressure in the crankcase can cause a lot of seals to fail.

Valued Contributor
Posts: 3835

Reg: 04-15-05
01-26-20 03:09 PM - Post#2785233    
    In response to badbob85037

Is there some sort of venting on the one valve cover the PC Valve IS NOT fitted to?

The way the system works is, vacuum from under the carb pulls oil vapor through the PC Valve, into the air cavities inside the engine, and up into the opposimg valve cover, through a fitting to a large diameter hose, to the clean air area of the valve cover, or, some sort of filtered oil cap.

If the air inlet either isn't there, plugged, or simply not done right, the air area inside the engine doesn't allow adequate venting of air pressures caused by the undersides of the operating pistons, and pressure builds, oil vapor isn't vented through the PC Valve system correctly, and oil can be pushed through the rings and valve guides, and oil exits the engine any way it can.

The give away was that the PC Valve was blown out of its valve cover holder, from inside engine air/oil vapor excessive pressure. Fix the venting on the valve cover, other side of the cover with the PC Valve on it.


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