PCV valve

[cdeal28078]

Is there a way to tell what valve to put in an engine? I was having trouble with my 460 getting oil all over the top of the valve covers, around the dist. and on top of the water pump. I used a PCV valve for the engine which is a 76-77 460 from that model Super-cab truck. I finally pulled the dip stick and put a rubber cap on the tube and the engine has been clean for a month or more. SO I figure either the dip stick is letting oil out too easily or the crank case is getting too pressurized because of a wrong PCV valve. I have seen a wrong valve cause oil to come out of the dip stick tube on an late 80's Mustang with a new 351W in it before and I know that we put the right valve back in it and it fixed it.
My 460 is not stock but is not a hot rod either. It is a D1 stock block with D3 stock heads. Performer intake, Hedman headers, 600 Holley and a Comp Cams 256H-11 cam that is real mild. By the book at the parts store I have the right weighted valve in there but I figure I have changed things on the engine and wonder if another lighter or heavier PCV Valve would solve my problem
Anybody have any ideas?
Thanks
Clint

[ArizonaDan]

Alright, here we go again with my favorite troubleshooting and tuning topic; vacuum.

Apologies to you if this seems overly simplistic but not being familiar with your troubleshooting skill level I thought I would throw this out there for your consideration.

Have you hooked up a vacuum gauge to measure exactly how much "suction" is available to "pull" the crankcase pressure out and through your pcv valve? A generaly accepted standard for gasoline engine vacuum is 19"-21" while idling at sea level. Subtract 1" of vacuum for every 1,000' of elevation above sea level.

Crankcase ventilation is a factor of both crankcase pressure pushing AND vacuum sucking on the pcv valve. Weak vacuum will contribute to increased crankcase pressure that leads directly to external oil leaks like you describe.

Larger than stock camshafts can cause slightly reduced vacuum during engine operation. However, vacuum levels in your engine can be either increased or decreased by simply adjusting the base timing of your distributor. Be aware that this adjustment will affect the entire timing profile of your engine. Start by determining how much vacuum you have available as your truck runs right now. This will be your baseline reading.

If your vacuum is low then try to locate the cause of your low vacuum. Cracked vacuum hoses, leaking distributor diaphragm, leaking transmission modulator (if autmatic trans.) and brake vacuum boosters are all items that must be checked. If there are no vacuum leaks then try adjusting your base timing to increase vacuum. Advancing the base timing increases vacuum up to a point. Too much advance leads to preignition so be careful when doing this.

I would stick with the stock pcv valve even on a moderately built engine until I had accurately measured and determined what my operating crankcase and vacuum pressures were. Only if it can be determined that the stock pcv valve simply will not provide adequate crankcase ventilation for the specific operating conditions of your engine would I try to locate a non-stock pcv valve that will meet your engine's requirements. How you would determine which pcv valve will meet your needs may be difficult. To the best of my limited knowledge pcv valves are not typically rated by their operating pressures. You may be able to find this info somewhere but I can't offer any help in that area.

Good luck

Dan (vacuum, vacuum, vacuum!)

[ToughOldFord]

Something to check for is a PCV hose that is collapsing in on itself under vacuum. Newer hoses are weak and don't hold their own after a very short period of time. Here's how some of us solved this problem:

http://www.fordification.com/forum/view ... 15#p218001

Looks like Blue's pics are gone, but you can still see mine.

[cdeal28078]

Thanks for the suggestions. Operating at idle it has around 18 inches of vacuum. Hoses are all good. Pretty new Valve.
I am running around 12 btdc initial timing with total coming in around 2800rpm at about 34 BTDC not counting vacuum advance.
It doesn't have enough cam to hurt my vacuum. it is a 256h which is .514 intake and exhaust and 210-218 at .050 I think the lobe separation is 111. Is that enough to hurt my vacuum? Can't see it since I am idling around 800 with 18 inches.
The 1st pcv valve I bought for it was for something like a 70 Lincoln with a 460. It would sit there and vibrate at an idle. I could hear the weight jumping up and down. I bought this valve for what the engine came from a 77 truck with a 460 and it stopped the rattling.
I just need to know more about how they rate the valves. I know that on the bottom side there is a stamp on the metal weight and they were different between the 2 I have had.
I can't believe more people with hot rodded engines don't have more trouble with this. I have looked all over the net and find very little about it.
clint

[ArizonaDan]

18" vacuum at idle is excellent. Lack of general vacuum is not your problem, excessive crankcase pressure may be a remote possibility. But first, did you measure the vacuum at the PCV valve/carburetor port? Good vacuum at one port doesn't necessarily mean all the ports are flowing correctly. Measure the vacuum at the actual PCV/carburetor port if you haven't already. If suspect, spray liberal amounts of carb cleaner into both the carb port and the PCV hose and measure again to see if there is any change.

Here's another suggestion:

If your vacuum gauge is a compound gauge, i.e. reads both vacuum and pressure, then figure out some way that you can attach it to your oil dip stick tube tightly with a hose and clamp and route the gauge somewhere that you can observe it while you safely drive the truck. There may be another tapped port into the crankcase somewhere on the block where you can plug in a pressure gauge to read crankcase pressure. This will allow you to read actual crankcase pressure under all engine operating load conditions.

I can't tell you what acceptable crankcase pressure should be but any reputable engine builder with FE familiarity should know.

From my understanding of PCV valve operation they not intended to facilitate complete evacuation of crankcase pressure into the intake system but rather to regulate a happy balance between unavoidable crankcase pressure build-up and critical induction system vacuum. Too little restriction in the PCV circuit (or the wrong PCV valve) will have the effect of a vacuum leak, which will detrimentally affect your ignition timing, shift points if automatic transmission and braking operation if power assisted brakes. Too much restriction in the PCV circuit will cause excessive crankcase pressure and all of the external oil leak conditions that you described in your first posting.

I still suspect your oil leaking problem is something relatively simple but I am just throwing out any troubleshooting ideas I can think of related to your descriptions. Is it possible you just have leaky gaskets and seals?

Good Luck,

Dan

[BobbyFord]

You can also install a breather-type oil fill cap on the valve cover opposite of the PCV valve cover to alleviate crankcase pressure issues.