Hey everyone, I've been trying to track down the source of oil blowing out of my 292 when I'm driving it. The engine is out of a '72 C10. I have a PCV valve with a hose to the air cleaner. The oil cap is a non breather type. I welded a baffle inside the valve cover to keep oil from slinging up into the PCV valve. Oil seems to be pushing out the valve cover seal and coating the block in a thin film. I bought all new seals for the engine before I installed it and it doesn't leak more than a few drops from the oil pan when sitting. I've moved the breather to the intake with the same results. I'm ***uming the engine is building pressure somewhere and it has nowhere to go, but I don't know what else to try. Intake is stock with a single Rochester carb, exhaust has been split by me. Thanks all, NAES
Post a couple pictures, showing what you have. It's hard to tell from your description. The PCV valve needs to connect to vacuum at one end, and into the valve cover at the other end. There needs to be a breather, either to outside air (open PCV system), or to the air cleaner (closed PCV system). And the PCV valve and breather need to connect to baffled openings in the valve cover, which some aftermarket valve covers don't have, but factory ones do.
squirrel you are correct. you can also eliminate the pcv valve and run a couple of push on breathers like the old days. i weld 3/4 pipe to the valve cover openings and use push on breathers. the engine has to breath.
Do you have an aftermarket valve cover? IME they frequently dont quite fit and cause this exact problem.If you clean the engine off,remove the pcv hose and run the engine does it stop or slow the leak?Have you done a leakdown test on the engine? That will show up leakage by the rings right quick.Like Squirrel said,pictures!
I agree, it sounds like your PCV is hooked up wrong. Another mention is the gaskets. I tried running rubber gaskets like I do on all the v8s, but I couldn't get them to stop leaking on my straight six. I switched them out with plain old cork and now she's happy.
This is a generic drawing of a PCV system off the net that I saved years ago but it does show how the system works. I'm not a big fan of just running a couple of breathers on any engine except maybe a drag engine as if you drive one set up like that very far you are going to get at least some oil film out on the top of the covers as it is all venting pressure out and not flowing through and drawing the fumes off to be burned inside the engine.
Unhook the PCV and make sure you are getting good suction from the intake, if not, the line is plugged. On 250's, there is a curved tube going into the intake, where the hose hooks to, that is where the restriction usually occurs. Carbon build up.
The concept behind the PCV system is to create a slightly negative crankcase pressure. In addition to keeping crankcase emissions from entering the atmosphere, leaks are reduced . It sounds like blow by past the rings is overwhelming the capacity of the PVC system in this case, allowing positives crankcase pressure. Do a cylinder leakdown test and rebuild as required.
OK guys thanks! I'll do everything as requested and get back to you. As usual you all are a wealth of information. NAES
Pull the oil cap and see just how much blowby you are dealing with. If you see quite a bit do cylinder leak down test. A PCV system can only handle so much.
heres how I am doing my 292 pcv with a breather from Tom Lowe used 1/2 inch aluminium tubing wraps behind vavle cover and over to carb. Don't know if its going to work havn't fired her up yet. [/URL] [/URL]
Hey guys, here's a few pics of my setup. You can see all the oil everywhere. I did a compression test and all the cylinders were low. 100-110psi across the board which is obviously low. From the above reading it looks like I need to run a pipe from the intake manifold to the PCV valve in addition to the one that I have running to the air filter. Please let me know what, if anything I can do to figure this one out. Thanks as usual guys. NAES PS. I apologize for the images coming up sideways. I uploaded from my phone and it did that.
When I was having valve train and rocker problems with my nailhead the motor was trying to tell me by pushing a lot of oil out through the dipstick. Maybe make sure you don't have any broken valve springs, broken rockers etc.
Looking at your pics, it looks like you need a vented oil fill cap (breather). Pcv valve needs a place to pull fresh air from. Kind of like ****ing on a straw with your finger over the end, there's no place for air to enter. In a case where you have excess blow by, the pcv cannot keep up. Without venting the pressure will push oil past the gaskets.
Years ago a buddy of mine had a hobby tractor with a screaming *** sbc. He was very compe***ive and made a lot of full pulls. He ran twin breathers off the headers and would spin it 8500-9000 rpms. After a run he would come back to the pits with oil pushed out of every gasket. Another puller with an almost identical built motor was always clean. My buddy says, "I was always impressed with that guys motor. So one night I walked over to him and asked, How do you keep the oil from blowing out?" He said, "I don't, I just wipe it off after every pull."
As has been said several times before, the PCV needs to be connected to VACUUM. In the stock setup, the breather hooks up to the air filter and the PCV hooks up to a port on the Intake (might be on the carb itself, I haven't owned one of these motors in a little while). Positive Crankcase Ventilation requires a strong vacuum source to positively ventilate.
If your engine has excessive compression leaking past the pistons and rings. No PCV & breather setup is going to stop it from blowing oil. And the PCV needs full manifold vacuum. and a vented breather cap.
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