Author Topic: I need a bit of help... (Vacuum and PCV)  (Read 6359 times)


  • Member
  • ***
  • Posts: 21
    • View Profile
I need a bit of help... (Vacuum and PCV)
« on: October 10, 2010, 04:39:35 PM »
I feel a little dumb about asking what I'm about to ask, but I need some help from folks who know their way around an original 327. I've included pictures below to aid in what I'm talking about.

When I bought my 67 (with original 327, aftermarket Edlebrock Performer Intake Manifold and Carburetor) whoever had done the motor work had done some weird stuff to it. The plain jane chrome valve covers they used had a total of four breather caps, and no PCV set up. The thing was slowly blowing oil all over the valve covers, as I suspect the crankcase has too much pressure in it, and fine particles of oil were getting all over. I was constantly having to wipe it down. Also (see pictures below), there was this 'thing' that I would like to assume is some type of original PCV valve, at the back of the engine near the distributor. The vac line coming off of it went to the main vac port on the carb. Well, I decided to figure out what was going on, and dig into this a little bit.

So, I pulled off the main vac line to the 'thing', and discovered that someone had plugged the main vac tube in the carb with a sealant, and in the hose attached to it, had stuffed a tire valve cap and more sealant. Obviously to prevent it from doing what it was suppose to do. I figured this was the source of my problem. So I set out to buy new valve covers, with only two holes (one in each cover for for breather caps, and PCV valve) instead of the four I had. I got them installed, put on a new Edlebrock breather cap in one, and in the other, I hooked up a PCV valve and ran it to a 'T' connector at the main vac port on the carb, and hooked it up. On the other end of the "T" I hooked up that original vac line that was clogged and going to the 'thing' at the back of the engine. (Yes, I cleaned out the tube, and cut off about 2 inches of vac line to get out the sealant and the valve cap). I also took the time to change my spark plugs (the old ones came out, did not look completely 'normal', and appeared to be slightly 'wet', with a mild build up on the 'ground' (side) electrode). I gapped the new ones at .035).

Anyway, the engine is burning oil... slightly. I can see it exit each exhaust pipe... so whatever is causing the oil to burn is happening on both sides of the engine (as I have a dual exhaust system). I have not done a compression test yet, but am about to. (Side note, any idea of what kind of compression I should be seeing in this stock 327 on each cylinder?)

I figured the most likely culprit of this oil situation is the incorrect PCV set up... and before I go crazy, I'd like to know everything I'm dealing with... and for starters, WHAT is this 'thing' in the back of the engine block near the distributor? I don't believe it to be a oil pressure sending unit...

Let me add, I'm a novice when it comes to motors. I can do just about anything else with this car, and understand the fundamentals of engine operation, but am admitting to needing help with the more intimate operations of an engine, and this problem.

Any constructive help/criticism would help me. Thanks for your time everyone...

and I have it set up now...


  • CRG Member
  • *****
  • Posts: 4365
    • View Profile
Re: I need a bit of help... (Vacuum and PCV)
« Reply #1 on: October 10, 2010, 05:55:02 PM »
Nice photos - makes it easy to diagnose!

The PCV system works by having manifold vacuum "suck" outside air into and through the crankcase, and then through the PCV valve (which meters the flow), and into the intake manifold, where the crankcase vapors are mixed with the incoming fuel/air charge and burned.

In '67, the standard engine ventilation system (shown in the Assembly Manual in UPC 6, sheet C5) used the adapter at the rear of the block (the "what is this" in your first two photos) with a hose to a PCV valve and a fitting at the rear of the carburetor base; outside air entered the crankcase through the vented oil fill cap on the oil fill tube at the front of the intake manifold.

The optional "closed positive" ventilation system (shown in the Assembly Manual in section K24) was a little different, and the flow direction was reversed from the standard system. A different adapter was used at the rear of the block, which connected via a hose to the air cleaner base, on the clean side of the filter element; this was the entry point for outside air into the crankcase. The exit point was the oil filler tube, which had a threaded bung in it for the PCV valve, then a hose to the carburetor base; the oil filler cap was sealed, not vented. Air entered the crankcase from the air cleaner, through the adapter, through the crankcase, then exited through the PCV valve on the oil filler tube, through the hose to the manifold vacuum connection on the carburetor base.

Your setup, as you received it, had no ventilation at all - only pressure relief through the breathers on the valve covers; it should have had a PCV valve where the hose connected to the carb base instead of being plugged, and the aftermarket intake manifold eliminated the original oil filler tube.

Your current setup with the "T" has a huge vacuum leak (from the "T" to the adapter at the rear of the block). To make it functional (and eliminate the vacuum leak) you can remove the "T" and do either of two things:

1. Run the hose from the PCV valve to the nipple on the carb base and cap off the nipple on the adapter at the rear of the block; that will use the breather at the rear of the passenger side valve cover as the entry point for outside air into the crankcase. Or,

2. Run the hose from the PCV valve to the nipple on the carb base. Run a hose from the adapter at the rear of the block to an elbow in the base of the air cleaner (Edelbrock has the elbow, and there should be a "knockout" in the air cleaner base where it attaches) as the entry point for outside air, and replace the breather on the valve cover with an oil fill cap.

Either of the above will give you a functioning PCV system, and will stop the oil misting.

'69 Z/28
Fathom Green