[mklinger]

It's been discussed a lot throughout the years of the importance of properly ventilating one's crankcase. I agree that the pontiac engineers had it correct by I have discovered that this is not easy to replicate without some effort if your build is not 'factory'. By effort I mean that you can not rely on the the off the shelf replacement and aftermarket parts doing what they were supposed to do 50 years ago. So here's the story.

When I built my last engine I needed a PCV valve. I went to my trusty auto parts store, gave them the vehicle and they gave me the part that was called for. This PCV valve was stamped '2020' on the body. Installed it and away I went.

Now I know I need breathers so I purchased (2) valve cover breather that looked like they would do the job and because I didn't want oil all over the valve covers since I was not running back to the air cleaner like the factory did I purchased baffled grommets. Installed it and didn't look back.

Engine runs great but I have this annoying drip out of the rear main. I am damn sure that the seal was installed properly so after some thought I decide to backtrack through the components related to the crankcase ventilation and here's what I find.

1. Maybe it's the PCV valve.

I check the original part numbers from Pontiac and they call out a 'CV-697C' and if you cross reference that you will wind up with a part that looks like the one I have stamped '2020'. On a lark, I go on Ebay and purchase a vintage CV-697C for about 15 bucks.

Here's what I found. Look at the difference in the size of the pintles. Vintage CV-697C on the left vs. the 'one size fits most' 2020 on the right.



Tom Vaught on here has said that a properly sized PCV valve should flow about 4 CFM and I would assume the factory original did. I doubt the current replacement part does the job. Buy yourself the right part, the vintage CV-697C. There are plenty on Ebay.

2. Maybe it's the breathers.

So I pull the breathers and just to test that they flow air I blow through them. Slightly restricted because there is some foam in them but they seem OK. Then I pull the baffled grommets and blow through them. I am able to blow next to nothing through them due to their design, a hairline slit between the upper and lower baffle. For grins I insert the breather into the baffle and blow again. Now, absolutely nothing. The bottom of the breather is applying pressue to the baffle so it can not flow at all. This engine is not breathing.

3. Maybe it's everything and I just got it completely wrong the first time.

At this point the PCV valve is replaced with the correct CV-679C part. Because I was using aftermarket aluminum valve covers, the factory tube to the aircleaner on the passenger side was not an option as was the oil filler on the drivers side. My current path is -10AN fittings and hose to the filtered side of the air cleaner with no restrictions from both valve covers. I suspect with this configuration the PCV will suck and the crankcase will breath and any positive pressure that may have been causing my rear main to weep will be in the rear view.

What did I learn? Don't just install the parts, make sure they are doing the job you and some engineer 50 years ago expected them to do.

Just sharing my recent experience. Hope this helps someone.