moper
Well-Known Member
Theres only one place pressure comes from: the rings. So you have an issue with the PCV, ring seating, ring seal, or all of them. Oil pumps and exhaust valves wont affect it.
Theres only one place pressure comes from: the rings. So you have an issue with the PCV, ring seating, ring seal, or all of them. Oil pumps and exhaust valves wont affect it.
Compression and leak down tests are both good so I doubt it's the rings. Exhaust valves staying open when they shouldn't will also cause pressure to leak past the valve seals.
Um... no it won't. Race engines don't even use exhaust valve stem seals and they don't have pressure leaking into the crankcase. Only way for pressure to get into your crankcase is through the rings.
If the engine was still in the car I would have said to run it with the PCV and breather removed and see how much blowby comes out when it's warmed up and idling.
Are you seeing any signs of oil on your spark plugs, either on the electrodes, insulator, or around the threads?
Plenty of people run without a hose hooked up to the air cleaner. I have a big breather and pcv. Sure I could find a way to vent all this pressure but this pressure is telling me something is wrong.
Yes, they do and they are running it WRONG if it's a street car. Without the system being complete and AS DESIGNED, any diagnosis is ineffective. Lots of people drank the kool aid Jim Jones served, but they were WRONG too.
OK, I just asked as oil in the chambers can fool you with 'optimisitic' compression and leak down readings... the oil can seal things up better that they really are when operating.
Fair point. I'll be honest I'm not even really sure what purpose that fulfills. I saw the diagram but what does that hose do that a breather and pcv doesn't? I know there's no significant vacuum at WOT so the PCV isn't as effective but wouldn't that be the same case at the air cleaner?
This has nothing to do with what I said. Yeah if the exhaust valves are shut when they need to be you are in fact correct. Please read where I had oiling issues and bent some pushrods last year. Logic would lead me to believe I probably messed up my valve guides as well to some degree.
Plenty of people run without a hose hooked up to the air cleaner. I have a big breather and pcv. Sure I could find a way to vent all this pressure but this pressure is telling me something is wrong.
Well, actually there is TONS of vacuum at WOT, just not where YOU'RE thinking. Engine vacuum falls off on acceleration, yes, but vacuum increases severely at the air cleaner going into the engine. That's the other half of the PVC system. When one side falls off, the other side reverses flow into the engine intake pulling the crankcase gasses in through the air cleaner on the other side. This is why often times when you leave the breather disconnected from the air cleaner, you get oil all over the valve cover. That same oil mist can also over come the rings at high RPM and get blown out through the combustion chamber.
The PCV system works good only TWO ways. 100% complete, OR 100% eliminated. I like the system, because on a street car, it actually helps keep the rings sealed and keeps oil consumption down.
On the older cars (mid 60s and prior) they used "OCV" or open crankcase ventilation, which had what was called a road draft tube that stuck straight down into the air flow under the car. All it did was dump the crankcase vapors right into the atmosphere. At least with the PCV, not only are those vapors burned, but an active vacuum is put on the crankcase, helping to keep rings sealed. It's really a win/win.
Yes, people have run "only this" or "only that" for like ten thousand years and "never had a problem", but how would they know the difference if that system had never been complete?
What some of us are trying to get at is: your engine may not actually have too much blowby it just doesn't have a good way to vent the pressure. Now that the engine is out of the car you can't monitor the actual amount of blowby being pumped out by the engine so now all you can really do is play Detective and tear down the engine looking for clues.
I had intended to try just running double breathers for a bit but never got around to trying it. My dad built a nearly identical 318 8 years ago and never had any of these issues which is what I'm basing most of my reasoning on. Chances are if he got away with the setup he's running (the same as mine) then the issue is definitely elsewhere. There may be a more effective way to manage to blow-by for sure but right now my main concern is definitely tracking down the source. A fresh mild 318 shouldn't be having these problems.
No offense but from my experience that kind of thinking leads to nowhere ("it worked with his setup so it should work with mine"). Your dad probably got lucky that both the breathers he happened to use could flow enough that the crankcase didn't over-pressurize. When the PCV valve senses pressure it shuts and forces the crankcase gases out the breather side; with 2 breathers the engine has 2 big holes to vent out through at all times.
No he's running PCV and breather like I was.
I keep having an oil leakage problem. I have a pcv valve on the drivers side cover, and a breather on the pass side. No oil showing up anywhere on top, but can`t keep the stud girdle sealed, about ready to scrap the dam thing. I `ve tried about every sealer known to man on it, checked the shims multiple times on the studs etc.Think of the PCV system as an unbroken circle, beginning with the inlet at the air cleaner and ending at the outlet for the PCV valve. Without all the components, you WILL have issues on a street driven car. Here is a simple diagram.
View attachment 1715254715
Compression and leak down tests are both good so I doubt it's the rings. Exhaust valves staying open when they shouldn't will also cause pressure to leak past the valve seals.