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Discussion Starter #1
Once again I come to you all who know way more than me. I have been chasing an oil leaks on my new BB 468 for a couple months. My leaks are not major but once I repair one it springs a small leak somewhere else. Do I have too much crank case pressure? I have a pcv valve (AC Delco for a 70 big block) on the pass side to the carb base and a K&N breather on the drivers side front. My leaks were coming from the valve cover gasket..fixed …a trickle from the rear of the manifold and from the corners of the oil pan..fixed…now I see drips from the rear seal area and the front of the pan. I am chasing my tail here and need some help. The motor runs strong and has about 400 miles on it. Do I need to wait for rings to seat? My oil looks kinds dirty to me already….I did a search for pcv and have read many different opinions on pvc location…etc My motor is nothing fancy with a mild cam. My vacuum is about 11 at idle if that helps at all. Is there any way to measure the crank case pressure? How can I relieve it if is an issue? Any help would be greatly appreciated..
 

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You may need a PCV for a Z/28 or a 375 HP/396 CID since the manifold vacuum is low - PCV will have a weaker spring allowing it to open under less vacuum. However, the valve woul dbe open upon deceleration, max vacuum.

I haven't seen one in years, but there is/was a flowmeter device, 2 inch diameter gauge, one would place over the oil fill hole and it indicated either vacuum or pressure of the crankcase.

If crankcase is pressurizing, one would see oil at the filter on the valve cover much like seeing oil in the air cleaner base of an OE set-up.

An old shadetree trick is to remove oil fill cap and place hand over tube with engine running and after 30 seconds, one should feel a vacuum, if it was sucking/working.
 

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Discussion Starter #4
Thanks guys...

Everett...ant clue as to an AC Delco part # for that specific pcv for a 375 hp BB I figured that a 70 BB 454 was in that range. I'll try to search it up and see if i can find a part #

Thanks

PS Kev...got my tranny jack today...not too shabby!
 

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Gary,
If you have a breather on one valve cover, that should eliminate most pressure. Having the pcv valve is just a plus and the engine should run fine without it. Dont forget that most engines up to the mid 60,s simply had breathers with no type of pcv system at all.

There is a blowby gauge available that you can put into one of the valve cover holes, then block the other one and actually measure blowby cfm at various rpms and under a load. I forget the exact numbers that are acceptable, they are on the instructions sheet in the gauge at the shop :) Pull the breather and the pcv valve and rev the engine up some and see if you can feel or see any smoke coming out of the valve covers. If you can feel air coming out, you probably have too much blowby :(

If you do have a blowby problem, the only way to solve it is to find out why the rings are not sealing and fix that problem. Modern rings should be pretty much seated on the engine stand if the cylinders were properly finished.
 

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736V is the one specified for '69 302 and the 375hp 327 Corvette low vacuum engines. I would not call 11" of vacuum at idle a mild cam but some who race might.
 

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Discussion Starter #7
Thanks everyone for the info...I will check things out and get the pcv valve replaced again.

One more question: I have a 7 qt moroso oil pan and a high volume oil pump that is giving me around 75+ psi at startup idle and drops down after warmed up but usually in the 60's driving around locally. Maybe down in the 40's at idle when hot. Is there too much oil pressure that could be contributing to the oil leak? Thanks a bunch
 

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Discussion Starter #8
Anyone have a part # for an ACDelco pcv for a 375 hp big block or a sb302? I tried my local parts counter but they couldnt find a valve other than just big block which is what I already have. According to above I may need a pcv from a lower vacumme motor. Steiner gave me a part # above but they didnt know what that # was. These guys are usually pretty good and not an Autozone or Pep Boys chain parts store. The showed a valve in Fram and in Standard but looked it up and it wasnt available anymore ???

Any info would be appreciated
 

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You might check the oil filter book at Pep Boys or other DIY and see about crossover part number. NAPA would be a good place. So would www.hemmings.com.

Higher oil pressure does make for more oil being thrown around, especially at the top end if the the block galleys have not been restricted to limit amount of oil to the top. The pressures you see are inline. I have the same set-up except I asked for 0.003" clearance rather than 0.002" and I get 20 PSI at hot idle and 50 PSI at 5K rpm.
 

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736 is a standard number (full number CV736V) and the one I have is a Purolator. If you ask for one for a '69 Camaro 5.0 liter 302 that number should come up at Advance or AutoZone. The Frams that I have seen are cheap plastic whereas the Purolators are metal.
 

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Discussion Starter #12
Thanks Steiner

736 is a standard number (full number CV736V) and the one I have is a Purolator. If you ask for one for a '69 Camaro 5.0 liter 302 that number should come up at Advance or AutoZone. The Frams that I have seen are cheap plastic whereas the Purolators are metal.
 

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Gary,

Just my opinion ...... I think you are wasting your time looking at the pcv valve for an answer to your oil leak issues. If it was a crankcase pressure problem you would be puffing smoke from the breather or pushing the dipstick out of its tube under load. You should be able to remove the pcv valve completely and run 2 breathers and still not have an oil leak. How many race engines do you see with pcv systems on them ? Do they leak ?

Same with the high pressure pump .... it will not cause an oil leak except for at an oil galley plug that is not sealed correctly.

What you have is a leak ..... you need to find where the oil is leaking from and fix the problem. Simple as that.

Start out by buying a $5 bottle of leak detecting die at the parts store and a $6 UV light bulb from Wal Mart. Put the die in the oil, drive it a few miles than use the light to see where it is leaking from. You would be surprised at how far oil can run, or get blown around an engine before it decides to drip off. Your drip in the back could very well be from a valve cover gasket at the front of the engine. The die glows bright yellow and allows you to see exactly where the oil is coming from.

Forget about the PCV valve .... fix the leak.
 

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What kind and weight of oil are you using.Low viscosity synthetic oils are notirious for making it past the seals on older engines.This is why newer engines have such better gaskets systems.Center bolt valve covers,RTV in place of manifold seals,one piece pan gaskets with stiffening rails on the pan.Cast pans,valve covers and front covers.All these things were done to make the engines seal with modern near zero weight oils and high tempatures.Unless I have a vacum pump on a big block,there is always a little dampness or a little hanging drop of oil on the bottom of the engine somewhere,even with 20/50 weight.You can litterally chase leaks for so long that eventually you start making more leaks fixing the ones you already have.
So whats your oil weight/type?
 

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Discussion Starter #16
Hi Bill...thanks again. Yes I already did the dye and black light. I had a small leak from the valve covers and a dribble from behind the rear intake manifold. I didnt use the rubber gaskets for the manifold just "Permatex Right Stuff". I dug out the seler a bit and re sealed it as I did the valve cover gaskets. I then saw the small dribble comming from the corners of the pan gasket. I think I stoped those and put in studs in the 4 corner screws of the pan. Now I see what it looks like comming down the center of the rear of the pan and when I took the flywheel off (tranny out for warranty repair)its a little wet up around the crank seal. Its like I am plugging up a dam and it springs out somewhere else. I'm pretty much going to live with it this season cause i dont want to take the motor out just yet. I think your right that its just a leak and I did do two breathers for a while and it still didnt help.
At this point I'm going to enjoy the car cause I just recently got it on the road and want to put some miles on it.

Gary,

Just my opinion ...... I think you are wasting your time looking at the pcv valve for an answer to your oil leak issues. If it was a crankcase pressure problem you would be puffing smoke from the breather or pushing the dipstick out of its tube under load. You should be able to remove the pcv valve completely and run 2 breathers and still not have an oil leak. How many race engines do you see with pcv systems on them ? Do they leak ?

Same with the high pressure pump .... it will not cause an oil leak except for at an oil galley plug that is not sealed correctly.

What you have is a leak ..... you need to find where the oil is leaking from and fix the problem. Simple as that.

Start out by buying a $5 bottle of leak detecting die at the parts store and a $6 UV light bulb from Wal Mart. Put the die in the oil, drive it a few miles than use the light to see where it is leaking from. You would be surprised at how far oil can run, or get blown around an engine before it decides to drip off. Your drip in the back could very well be from a valve cover gasket at the front of the engine. The die glows bright yellow and allows you to see exactly where the oil is coming from.

Forget about the PCV valve .... fix the leak.
 

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Discussion Starter #17
Hey Rich...I have been using the older Rotella 10/40 and adding some DDP. My pressure is about 75-80 at startup and calms down into the higher 40's. I think I'm chasing my tail and its a leak I can live with.(for now) I am very anal with things and thats why I am thinking I should just relax and enjoy the car. Cruise nights are just starting here in NJ and I want to get my 67 out to as many as I can just to have some fun. I made a few last summer and it made me feel like I was 18 again only with kids in the back instead of girlfriends..(imagine that!) Last thing i need is to have my motor on a stand looking at my oil pan while the season rushes past..:)


What kind and weight of oil are you using.Low viscosity synthetic oils are notirious for making it past the seals on older engines.This is why newer engines have such better gaskets systems.Center bolt valve covers,RTV in place of manifold seals,one piece pan gaskets with stiffening rails on the pan.Cast pans,valve covers and front covers.All these things were done to make the engines seal with modern near zero weight oils and high tempatures.Unless I have a vacum pump on a big block,there is always a little dampness or a little hanging drop of oil on the bottom of the engine somewhere,even with 20/50 weight.You can litterally chase leaks for so long that eventually you start making more leaks fixing the ones you already have.
So whats your oil weight/type?
 

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It's not uncommon to have to RE-Torque an Oil Pan after a few hours of Engine run time as the Pan takes Set due to heat.

A PCV System is definitely necessary for any Street Driven car compared to a Strip TOY that can get away with Valve Cover Breathers . Generally the PCV Valve is installed on the Drivers Side Valve Cover where there is less Oil Vapor Density compared to the PSGR Side due to Windage. You should also run a Hose from the Breather on the PSGR Valve Cover to the Base Plate of the Air Breather as the PCV Sytem does not work when the Throttle Plates move or at WOT because there is no Vacuum - The Air Breather Hose to the Air Filter Base Plates takes over under this condition.

If you do not have a PCV System, creating Negative Crankcase Pressure, on a Street Ride, you will eventually have Oil Pan Gasket Leaks, Intake Gasket Leaks. Valve Cover Gasket Leaks and blow the Crankshaft Seals.
 

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If you ever get around to taking the engine out for a full reseal,here are some things that work real well for me.I glue the pan gasket and end seals to the block with yellow snot glue.I use dabs of RTV at the corner of the gasket to seal,then after I bolt the pan on,with everything perfectly dry,clean and tight,I run a bead of RTV all the way around the outside of the pan/block seam.I use a wet finger to smoth it out.Latly,I have been taking a razor and cutting off any excess gasket that hangs out between the pan and block before putting the silicone in.I like this because sometimes cork gaskts will wick oil through them so putting RTV on the outside seals them tight.

In the rear main bearing cap,I offset the seal slightly and also use very small amount of rtv between the cap and block.

I use RTV for the intake end seals.

I glue the valve cover gaskets to the covers with yellow snot.

These are all methods you will never see in an instruction manual.

Good luck.
 

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It is kinda hard to see here because the RTV is the same color as the pan,but you can see that there is no visible seam between the block and the pan and no gasket sticking through the bead of RTV.All the RTV went on after the pan was tightened{except for the small dab on each corner),and while all the parts were super dry and oil free.If you do this when they go together you almost have to try to screw up and make it leak.You can also see that I followed all the way around the front cover gasket.Once you get past the weird feeling of dribbling spit on your finger it goes easy.

 
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