[461-69bird]

I've hooked up the pcv this year and seem to have a leak from the valve cover now. Is this linked?
The way I have it is pcv from valley pan to back of intake under the carb and a breather in each valve cover.
Any thoughts?

[chuckies76ta]

Your question is pretty vague. No offense. Have you tried just one breather? How high rpm you spinning the engine? What H/P? Is it also pushing the dipstick out some?

[AG]

The PCV valve only works when there is high manifold vacuum (idle) so it's unlikely the pcv is the cause of the oil leak. Usually leaks occur at high rpm as long as your not talking about a valve cover gasket. Also check the baffling under the breathers, when I built my brothers street motor it had a breather that was puking oil and it didn't have any baffling. We stuffed it full of SS wool and the puking stopped. I run evac tubes from my valve covers to my headers and never have any issues, but ring seal is very good.

[461-69bird]

I've only ran it on the street as yet so no high rpm. Dipstick tube looks dry. It's a 600hp engine. Didn't run the pcv last year and no leaks from the valve covers.

It's leaking from the valve cover gasket onto the header flange.

I'll check the baffling on the breather but
there's nothing coming from the grommet.

When I first ran the engine I had the pcv connected and it pushed the dipstick out. I can always go back to no pcv but wanted to try it again.

[JLMounce]

I had similar issues with the 455 in my Firebird.



In low load situations, the PCV valve is pulled almost closed and opens, providing additional flow during high load, low vacuum situations.

My issue was that cruising speed at 65 mph would be around 3400 rpm and my engine actually sees more vacuum here than it does at idle. As a result, the high sustained rpm, and highest vacuum situation for my engine caused enough positive crankcase pressure to blow oil out of the dipstick and create several seal blowouts in the engine.

The ring seal in my engine is not great, it sat for about 16 years and in that time I believe the rings lost a good bit of their seal with the cylinder bores, contributing to the problem.

My solution has been to remove the PCV all together and run a draft can setup from Might Mouse Solutions. I have -8an fitting attached directly to the tomahawk valley pan, plumbed to the draft can, then from the can to the back of the intake manifold.

According to MMS this provides enough crankcase ventilation for up to around 800 hp and the draft can is an air/oil separator. I have one open breather in a valve cover to provide fresh air in. Only in very high pressure situations would the can itself vent any blowby to atmosphere. So far my experience has been positive. I resealed the top of the motor and after the change I no longer push oil from the dipstick and the leaks have stopped, with exception of the oil pan gasket which will be an engine out operation to cure.

[Tom Vaught]

Another cutaway of a PCV Valve that does not look like the one above.

The PCV valve only flows about 4 cfm max flow under some conditions.

The valve is restricted at idle conditions where a 4 cfm change could affect the ability to have a smooth idle.
Most stock type engines will be between 12 and 16 inches of vacuum with any performance camshaft.
A camshaft with 255 degrees of intake duration and 6-8 inches of idle vacuum does not work well with most
pcv valves. This thread is in the race section.

Tom V.

[461-69bird]

Hi Tom

Yes mine has about 5" at idle. I put this in the race section because of my engine specs, even though I drive it on the street and to the track.
Like JL Mounce, I have about 10" when cruising at 60mph at 3000rpm. Do you suggest not using a pcv in my case? It does improve my afr with it hooked up though.

[krisr]

I run my valley fitted PCV into a sealed catch can which is then plumbed back into the manifold. Engine idles with about 6-7" vacuum and the catch can gets oil so I know the system is working for me. I also have 1.25" tubes in the valve covers and run a little K&N filter on each tube. It seems to work well, the engine doesn't stink at all since I hooked up the catch can either.

[461-69bird]

Krisr
My valve covers are set up the same way as you. Do you still have a pcv fitted or do you connect the valley pan outlet to the catch can? Sounds like the way JL Mounce has his with the oil/air separator.

[AG]

I would reseal your valve covers if they are leaking, maybe try using a 1/4" thick one and Ultra Grey RTV. I use 1" valve cover spacers on my race car that are secured directly to the heads with RTV and then I use a 1/4" gasket between the space and valve covers. The oil level in the heads never get above the valve cover spacers and I never have leaks.

[Tom Vaught]

Originally Posted by 461-69bird

Hi Tom

Yes mine has about 5" at idle. I put this in the race section because of my engine specs, even though I drive it on the street and to the track.
Like JL Mounce, I have about 10" when cruising at 60mph at 3000rpm. Do you suggest not using a pcv in my case? It does improve my afr with it hooked up though.

Because you still drive the car on the street, you will still have corrosive gases inside the oil pan that you need to remove.
Henry Ford 1 figured out that deal with his engineers and put a road draft tube on their engines.

Several friends ran engines on the street in the 255/266/106 c/l area and we wanted to keep the under hood less complicated, No belt driven vacuum pump. We installed a crankcase evac system in the pipes after the collectors. I ran 3" head pipes,
and good Walker mufflers, (no tailpipes).

If I was racing, I could swing the head pipes out of the way (lanyard supported) and have open headers in 15 seconds per header.
Simple with a little thought put into the system.

https://www.hotrodders.com/threads/c...t-work.193392/

Tom V.

[461-69bird]

Originally Posted by AG

I would reseal your valve covers if they are leaking, maybe try using a 1/4" thick one and Ultra Grey RTV. I use 1" valve cover spacers on my race car that are secured directly to the heads with RTV and then I use a 1/4" gasket between the space and valve covers. The oil level in the heads never get above the valve cover spacers and I never have leaks.

I have a 1/4 spacer on the head already and used the grey rtv too. Same set up last year and valve cover gaskets never leaked. Did have a leaky pan gasket last year which I have since replaced when had the heads done. The pan gasket is dry now but with the only change being the pcv, I have a valve cover leak.

[burd]

Drill out the valley a d put a PCV grommet in.

[Tom Vaught]

Originally Posted by 461-69bird

I've only ran it on the street as yet so no high rpm. Dipstick tube looks dry. It's a 600hp engine. Didn't run the pcv last year and no leaks from the valve covers.

It's leaking from the valve cover gasket onto the header flange.

I'll check the baffling on the breather but
there's nothing coming from the grommet.

When I first ran the engine I had the pcv connected and it pushed the dipstick out. I can always go back to no pcv but wanted to try it again.

A) "Didn't run the pcv last year and no leaks from the valve covers."
So did you run a breather or two valve cover breathers?

B) Since the valve covers are open to the pan, to blow oil out of the valve cover gasket at the header flange side, you need a lot of oil in the covers or pressure inside the crankcase/valve covers.

c) How old are the breathers, can you dip them in gas or solvent and make sure they are clean?

Tom V.

[461-69bird]

Tom
I have 2 breather tanks connected to the valve covers with clear 1" hose. I don't get any oil in the tanks but the breathers are old so will look at cleaning them.
If I put an air/oil separator in between the valley pan and intake, will this work like a pcv with my engines low vacuum?

[Tom Vaught]

When the engine is idling with a stock engine, you get about 2 cfm of crankcase flow.

When the engine is at part throttle around 35/45 mph you get the full 4 cfm flow.

when the engine is at WOT, you get maybe 1/2 cfm of crankcase flow as rarely does
any engine maintain zero vacuum unless it is a boosted engine.

With a Backfire you get full closure so that you do not set the oil pan OIL on FIRE,
which has happened with oil oil contaminated with lots of gasoline from poor ring seal.

Tom V.

[krisr]

Originally Posted by 461-69bird

Krisr
My valve covers are set up the same way as you. Do you still have a pcv fitted or do you connect the valley pan outlet to the catch can? Sounds like the way JL Mounce has his with the oil/air separator.

My PCV is still connected. Catch can is from Elite Engineering, it's made for an LS engine but with my RARE timing cover and SBC water pump, it all just worked using the 1 bolt in the head.