When my engine was rebuilt, the new manifold didn't have the road draft tube provision. So I ended up with breathers on the valve covers. Problem is that it mists oil something fierce out of the breathers. I installed a pcv in place of the one breather, but the other one still makes a mess. :mad Should I rig a pcv to that one too? Pizzes me off that I have to sort these things out instead of the shop getting it right the first time. Any suggestions? Thanks, Classic

 

A factory PCV system pulls air through the air cleaner to one valve cover and exhausts it from the other, through the PCV into the intake system. Otherwise it is a closed system. If you still have it, you should plug the road draft tube at the rear of the block.

RACE ON!!!

 

You definitely don't want to put a pcv valve in both sides. As CFI-EFI posted, the system needs a fresh air source (either through the air filter or through a breather as you have it). If the oil misting is severe you might be having a ring seal problem with the upper rings (excessive blowbly). How severe is this "misting"? Is it just an oily film around the breather or does it look like smoke coming out of the breather?

 

After 100 miles the underside of the hood is covered with oil. I have a hose going from the air cleaner to the pcv, but it isn't enough apparently. Everything in the engine is brand new. New pistons, rings the whole nine yards. :mad I was going to switch to synthetic oil, but that is out of the question now. I'd have to stop for oil more often than I have to stop for gas.Classic

 

If this is a new or fresh motor, make sure that all of the holes in the block are pluged with a bolt or a threaded plug.
Ther are a few locations to check: look near the fuel pump, timing cover area, & clutch pivot area.

 

You're terminology is kinda messed up. The tube on the front of the intake manifold is for oil fill and PCV mounting. If you don't have that, then you need a valve cover hole for oil fill and PCV, but probably not a breather (see below).

Do you have the original block with the breather hole behind the intake? Do you still have the oil vapor separator in the lifter valley? If you have both of these things, then the best thing to do is put the sheel metal tube and rubber hose back that plumb the breather hole back there up to the air cleaner. Now you have a fresh air intake to the crankcase with a proper vapor separator. You need a flame arrestor in the air cleaner too, so backfires don't get into the crankcase. Once you have this setup in place, change the breather cap on the valve cover to just a plain oil fill cap.

The PCV in the other valve cover should be plumbed to engine vacuum below the throttle plates of the carb.

If you no longer have the breather hole at the back of the block, then you need some kind of oil vapor separator in the valve cover.

A road draft tube is a tube that vents the crankcase to the air, hangs down below the motor, and drips oil onto the road as you drive. Outlawed in 1960 or so.

 

That could be the problem. The pcv valve needs to be hooked to a manifold vacuum source, typically at the base of the carb. The fitting on the air filter is there to provide fresh air to the crankcase to replace the air being drawn out through the pcv valve and also to reburn any fumes that make escape through that route.

 

Vetterodder is right. I missed where you said the PCV was plumbed to the air cleaner. It is not doing anything that way. The engine needs to suck air out of the crankcase through the PCV, by connecting the PCV to engine vacuum.

Your engine shop really should understand how all this is supposed to work.


[Modified by L79vette, 8:42 PM 5/25/2004]

 

I figured my terminolgy was not correct. I just did what the guy at the parts store told me. :banghead: I think the ig problem is the RPM air gap manifold. It didn't have the same provisions as the previous manifold.

So what I'm hearing is that I need to run the pcv hose from the valve cover to the carb. Then on the other side I need to run a hose from the valve cover to the bottom of the air cleaner.

The shop can't figure it out. The did such a great tune on it that it only ran on six cylinders and spit fuel out the top of the carb :confused: Obviously I'm no mechanic, but I'm pretty holley didn't design the carb to work that way. :D Classic

 

Sounds like you need to quit listening to your partsperson and also find a shop that has a real technician and not just some parts changers. Also sounds like you now understand what needs to be done. Most street carbs have a fitting at the side or rear for pcv connection and it's much larger than the other vacuum nipples. Because the carb fitting is designed to provide even distribution of the fumes, it's preferable to a manifold fitting which usually results in most of the fumes being drawn into only the closest cylinders.

 

Bad luck on the shop. Gotta find someone who knows what they're doing.

No problem with the RPM air gap. You just need to set it up the way a carbureted 350 is set up with holes in the valve covers, instead of the old style 327 way.

 

I have a short 2 inch length of hose coming off the back of the carb, that I teed off to split between my brake booster and my morphodite PCV setup. Its a tight fit against the chrome distibutor cover, but it does fit.
I have a cheap $8 edelbrock sealed breather serving as a cheapo pcv, and a regular breather on the other side. I plan on installing one of those billet breathers, and maybe include an inline pcv valve to keep the oil from going through the carb.
As for the oil mist... are you valve covers baffled?


[Modified by '75 383 ElkGrove, 10:49 PM 5/29/2004]