pcv valve and breather/oil filler tube

[dhamilton62]

I had a quick question. My old block 350 currently has the early style breather/oil filler tube in the front of the intake manifold. I was getting quite a bit of blow by and oil vapor seepage out of the breather cap so I swapped valve covers so I can run a breather and a pcv valve. After doing so, I didn't really notice much of a difference and can't feel any suction from the filler tube or breather hole on the opposite side valve cover. I was wondering if I needed to now plug up the old filler tube hole in the intake? Does that affect to suction and circulation that the pcv needs to work properly? I'm pretty sure my rings might be worn and that's the reason for the amount of blow by but just wondering if that would help. Thanks so much!

[markeb01]

Leaving the oil fill/breather cap in front will not affect operation of the PCV system. It will just act as another vent to allow fresh air into the engine.

What is more critical to diagnosing any issues, is how the PCV was connected previously. It should have been connected to one of the valve covers and feeding into the base of the carburetor. This would allow fresh air in the front, drawing fumes out from the side. If – the cap on the filler tube was a sealed cap and not a breather, you would have trouble and seepage because there would be no means to allow fresh air into the engine. This frequently results in leaking gaskets anywhere in the engine.

[dhamilton62]

Thanks so much for the response! If I kept the road draft tube, can I run two pcv valves, one on each valve cover and use the road draft tube as the source of fresh air? Unless I'm doing something wrong by only having the one pcv valve hooked up to the carb, I'm still getting lots of oil vapor residue out of the road draft tube where it drips over the motor after a 30 mile drive. Not too sure what to do at this point.

[Wrenchbender Ret]

You cannot run 2 PCV valves. Its obvious your rings are wore out. You need an o-haul or new engine. Putting a heavy oil in during the summer might help, like 20W50.

[1963c-10]

I have seen aftermarket valve covers with no baffles that can cause oil to blow by the breathers also. Especially if they line up right over the rocker arms.

But you said in post 1 you just had the old original style oil fill/breather tube. So I'm inclined to agree with the rest and probably due for a rebuild.

[markeb01]

Two PCV valves would be a bad idea, as the extra airflow would act as a vacuum leak. If you have a single PCV installed correctly, you should remove the road draft tube and plug the hole. It was replaced by the PCV valve to provide crankcase ventilation. You can run a breather on the original oil fill tube, and another breather on the opposite valve cover, but all the fumes should return to the intake manifold via the PCV valve.

If excessive oil emerges from the breathers once the road draft tube is eliminated, either the rings or valve seals are shot, and thorough compression testing is in order to determine what is needed next.

Another thought just occurred to me. If the engine has been apart, someone might have removed the baffle/can that lives in the intake valley at the rear of the block. This baffle eliminates liquid oil from reaching the breather pipe. Many people removed these back in the 60's & 70's not realizing the importance of the device. If you plug the road draft hole at the rear of the block, it won't matter if this baffle is in place or not.

[GASoline71]

Did 350's have road draft tubes? Thought that system went bye bye around the time the small journal 327's went bye bye.

Gary

[Marv D]

Your absolutely correct Gary. 67 was the last block with the road draft breather. And the 350 appeared in late 67 in large journal / new and improved (no road draft breather and available in 4bolt main) It didn't appear in anything but Camaro's until the 69 model year. Just more evidence of what mutations and rebuilders have put together from a 1/2 a century of compatible / interchangeable components.

[GASoline71]

So someone would have to turn a large journal 350 crank down to fit a small journal 327 block to still have a road draft tube and be a 350?

Gary

[cableguy0]

His 350 could also be a 327. Also I think there is some confusion on what the road draft tube is. It sounds like the fill/breather tube on the old style intake is being confused as a road draft tube.

[crazy longhorn]

Originally Posted by cableguy0

His 350 could also be a 327. Also I think there is some confusion on what the road draft tube is. It sounds like the fill/breather tube on the old style intake is being confused as a road draft tube.

I will agree, & try to expand a tad on that? I am old enough (been there,saw that)...maybe farting dust Ok, here goes....the road draft system ,did not have a pcv, just a road draft tube going out the bottom, & the vent tube on top of the intake. Along about 1962, they went to a pcv. The system still had the canister under the intake (as the road draft did), but had a pcv, that screwed into the carb, with a hose attached to a 90 degree fitting (same spot next to the dist, that the road draft tube had bolted). It still ran the tube & breather up front on the intake, till the end of 67. 68 made the change to the valve cover PCV, with the other side vented to the air cleaner. But don't you 'clowns" ask what I had for breakfast yesterday, I will not remember that ....Longhorn

[GASoline71]

Originally Posted by cableguy0

His 350 could also be a 327. Also I think there is some confusion on what the road draft tube is. It sounds like the fill/breather tube on the old style intake is being confused as a road draft tube.

Actually... that was my first thought too.

Gary

[cableguy0]

Originally Posted by crazy longhorn

I will agree, & try to expand a tad on that? I am old enough (been there,saw that)...maybe farting dust Ok, here goes....the road draft system ,did not have a pcv, just a road draft tube going out the bottom, & the vent tube on top of the intake. Along about 1962, they went to a pcv. The system still had the canister under the intake (as the road draft did), but had a pcv, that screwed into the carb, with a hose attached to a 90 degree fitting (same spot next to the dist, that the road draft tube had bolted). It still ran the tube & breather up front on the intake, till the end of 67. 68 made the change to the valve cover PCV, with the other side vented to the air cleaner. But don't you 'clowns" ask what I had for breakfast yesterday, I will not remember that ....Longhorn

Old people problems.....

[ERASER5]

If I wanted to know what you ate for breakfast yesterday, I would just check the dribbles on the your shirt. Old people, can't take'm anywhere.

Yep. no factory 350 had the front oil fill tube. But you could/can put an older intake on if you were so inclined. Edelbrock has an intake that can be cut to accept the front fill tube. So you can build that 383 stroker and pass it off as a 283... hmmm. What am I talking my self into?

[crazy longhorn]

I usually catch the good stuff in my beard....then I have snacks for later Longhorn

[cableguy0]

Originally Posted by ERASER5

If I wanted to know what you ate for breakfast yesterday, I would just check the dribbles on the your shirt. Old people, can't take'm anywhere.

Yep. no factory 350 had the front oil fill tube. But you could/can put an older intake on if you were so inclined. Edelbrock has an intake that can be cut to accept the front fill tube. So you can build that 383 stroker and pass it off as a 283... hmmm. What am I talking my self into?

Sounds like you just convinced yourself to stroke a 6.0 ls to slightly north of 400 cubic inches and giggle at the guys with a 383 when they try to race.
This is a terrible hobby. You see how I just emptied your bank account.