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289 PCV valve set up issue

2398 Views 28 Replies 11 Participants Last post by  AZ_Ryan
Hello all,

We have a freshly rebuilt 289 (60 over now) that is running smoothly. The cam was just broken in, and the car now can move under its own power (first time in 5 years). Before this rebuild, we had PCV from the passenger side into the air cleaner. Now, we have it coming from the driver side into the back side of the air cleaner, so it is a long hose run going towards the back of the air cleaner.

With this current set up we have been seeing a light amount of smoke (or oil mist from what I have researched) coming from the breather cap. We never had this issue before the rebuild. I have read in previous threads that it could be bad valve seats, or bad piston rings. The engine is as brand new, and the cylinder heads have a hundred miles or less on them. I would be so disappointed if either of those were the problem here.

This set up has worked before, and I am thinking this long (at least 14-18") run could be a part of poor PCV flow making it go out of the breather instead. Can you run two PCV hoses in one system? Should I replace the breather cap with a solid one?

Right now, the baffle on the PCV valve cover is NOT installed. Again, no issues before, but I can re install if needed. Let me know if you need any other information to provide the right answer.

Thanks!
Ryan
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Usually it’s PCV in the passenger cover, with a baffle under the valve, with hose to the manifold and breather on driver’s side, with hose to air filter or just a breather cap. Sounds like your long hose/intake setup is not pulling enough vacuum to make it work, provided there are no other issues (rings, etc). Non-PCV side should be sucking air in, not breathing oil mist out. Solid cap is not the answer.
 
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The PCV is a system, Positive Crankcase Ventilation. The valve cover with the PCV valve should have a baffle, and should have a 3/8 diameter rubber hose going into the intake manifold right under the carb. The PCV valve sucks air out of the crankcase, to be burned and go out the exhaust. The other valve cover is the air inlet. There should be an oil filler cap, with either a connection to the air filter housing for clean (filtered) air, or an open breather cap, where fresh air enters the crankcase. I think some minor smokey fumes after you shut the engine is normal, but make sure the PCV system is set up and working properly. One quick test is to run the engine and put your thumb on the bottom of the PCV valve. You thumb should stick right on there. Another test is to remove the PCV valve from the engine and shake it. It should rattle.
 

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There are 2 types of PCV systems, "open" and "closed". BOTH systems have the PCV valve installed (typically in the rear half of the RH valve cover) to remove vapors from the crankcase and the hose that is attached to the PCV to a manifold vacuum source, ideally into the intake manifold plenum or a carburetor spacer.

In the "open" system, a vented breather/oil filler cap allows outside air to be drawn into the crankcase to replace the fumes evacuated by the PCV. In the "closed" system, the breather/oil filler cap is connected by a hose to the air cleaner housing so that 1) the air entering the crankcase is well-filtered and 2) any fumes that may be expelled when the engine is turned off will be collected in the air cleaner housing to be burned the moment the engine is restarted.
 

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Hello all,

We have a freshly rebuilt 289 (60 over now) that is running smoothly. The cam was just broken in, and the car now can move under its own power (first time in 5 years). Before this rebuild, we had PCV from the passenger side into the air cleaner. Now, we have it coming from the driver side into the back side of the air cleaner, so it is a long hose run going towards the back of the air cleaner.

With this current set up we have been seeing a light amount of smoke (or oil mist from what I have researched) coming from the breather cap. We never had this issue before the rebuild. I have read in previous threads that it could be bad valve seats, or bad piston rings. The engine is as brand new, and the cylinder heads have a hundred miles or less on them. I would be so disappointed if either of those were the problem here.

This set up has worked before, and I am thinking this long (at least 14-18") run could be a part of poor PCV flow making it go out of the breather instead. Can you run two PCV hoses in one system? Should I replace the breather cap with a solid one?

Right now, the baffle on the PCV valve cover is NOT installed. Again, no issues before, but I can re install if needed. Let me know if you need any other information to provide the right answer.

Thanks!
Ryan
Do I understand that you have a PCV valve installed in a valve cover and no oil baffle underneath it?
 

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So reading this thread has me confused. The OP stated that theres a PCV in the driver’s side valve cover going to the air cleaner. This is simply not correct the PCV hose like others have stated should go to a manifold vacuum source aka the carb spacer or straight into some intakes but not all.

Step one is set up the PCV correctly.
Step two make sure the Valve cover has a baffle under the PCV to avoid unnecessary fumes from entering the intake manifold.
Step three make sure your have a breather/oil filler cap. Typically both the PCV and breather cap are in opposite valve covers. Refer to Bart’s post #5 for an explanation of oven vs closed systems.
 

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Discussion Starter · #8 ·
Do I understand that you have a PCV valve installed in a valve cover and no oil baffle underneath it?
...yes that is the current set up. It was taken out years back and I do not remember why. Possibly because the valve sunk too far in the valve cover and it touched the baffle? I'll be putting that baffle back in.
 

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Discussion Starter · #9 ·
Usually it’s PCV in the passenger cover, with a baffle under the valve, with hose to the manifold and breather on driver’s side, with hose to air filter or just a breather cap. Sounds like your long hose/intake setup is not pulling enough vacuum to make it work, provided there are no other issues (rings, etc). Non-PCV side should be sucking air in, not breathing oil mist out. Solid cap is not the answer.
I had hired a dude off craiglist to help with the heavy lifting on the engine install. He also did the valve tuning and did a fantastic job. It was his idea to have the valve covers as they are (he was a Pontiac guy). I will need to swap the valve covers as they have different sized holes on them for the breather and the valve. I knew it was different at the time but was not thinking ahead about the PCV set up.
 

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Discussion Starter · #10 ·
Possibly the rings in the new engine are not fully seated and you're getting some blow by. Why don't you have the PCV in the passenger side valve cover?
Outside of the cam break in, what is needed to ensure those rings are seated correctly? Ill be making the switch on the valve covers today so I can have the PCV go on a much shorter run.

The guy I hired to help with the engine install though this set up was best, but I did not have the foresight to think about the PCV.
 

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The PCV system on my 67 289: PCV valve in passenger side valve cover (has baffle), connected to the back of the carb for manifold vacuum. Breather cap in driver's side valve cover connected to the air cleaner. I believe this is a closed PCV system.

I like having the breather cap connected to the air cleaner as it brings in filter air into the crank case. I live in AZ and we have a lot of dust here.
 

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The PCV system on my 67 289: PCV valve in passenger side valve cover (has baffle), connected to the back of the carb for manifold vacuum. Breather cap in driver's side valve cover connected to the air cleaner. I believe this is a closed PCV system.

I like having the breather cap connected to the air cleaner as it brings in filter air into the crank case. I live in AZ and we have a lot of dust here.
So this is where Im confused…. The air cleaner, reguardless of the name, does not filter any air going to the breather. The breather has its own air filter inside at least the stock style does. You wont get any cleaner air into the crank case with a closed PCV system. But like Bart mentioned above the benefit is that when the engine is turned off the fumes that would otherwise leave the breather cap go into the air cleaner reducing pollution. Hence when the closed system was a California only thing. But the filter inside the breather also greatly reduces the vapor transferred into the air cleaner. In the end Im not sure there is a major difference here.
 

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^I don't believe closed breather caps have filters inside them. And if the stock ones did it certainly isn't doing its job after 56 years.
Ok either way for dusty environments the air filter wouldn’t filter air going to the breather cap. The air would have to go through the air filter then fight the vacuum from the carb and get pulled into the breather cap… I just dont see this happening. If anything the closed system would filter less.
 

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The breather cap is connected to a fitting on the base of the air filter. This fitting is on the inside (carb side) of the air filter so the breather cap (PCV system) is sucking the same filtered air going into the carb. Closed PCV system:

Hand Arm White Human body Cartoon


A breather cap that is not connected to the air filter base is just sucking in outside air. Open PCV system.
 

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Outside of the cam break in, what is needed to ensure those rings are seated correctly? Ill be making the switch on the valve covers today so I can have the PCV go on a much shorter run.

The guy I hired to help with the engine install though this set up was best, but I did not have the foresight to think about the PCV.
"what is needed to ensure those rings are seated correctly?". Typically, it takes approximately 500 miles of varied speeds for the rings to begin taking a "set". Might take a little more or little less. It depends on the type of ring and the cylinder finishing process. Most standard "street" rebuilds follow the 500 mile rule.
 

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The breather cap is connected to a fitting on the base of the air filter. This fitting is on the inside (carb side) of the air filter so the breather cap (PCV system) is sucking the same filtered air going into the carb. Closed PCV system:

View attachment 841736

A breather cap that is not connected to the air filter base is just sucking in outside air. Open PCV system.
So in theory I agree the air filter for the carb would filter both the air going into the carb and the breather. However this is only true if the air for the breather is being pulled from behind the air filter. I have never seen a 1965 or 1966 mustang with a air filter that fits snugly inside the air cleaner. In fact the ones NPD sells are quite small.

On another note most people don’t run the paper gasket that goes between the air cleaner and the carb… this is important to prevent unfiltered dirt carrying air from scratching cylinder walls.

The air filter, filters air in the blue section only and doesn’t filter air going to the breather….
 

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