Stupid question on crankcase ventilation

[Rick Piras]

I've had my 454 professionally rebuilt, and it puts out major horsepower, but is leaking oil from the front and rear main seals. Not huge amounts, but more than a new motor should. I called the shop and they said it's almost always related to crankcase ventilation. I have a vent on one valve cover, and a PCV valve on the other valve cover. I have the hose from the PCV running to the base of the carb, thinking that that way I'd always have vacuum. In doing it this way, have I created a "closed loop", and am no longer getting the correct venting? Will moving the PCV valve hose to the air cleaner correct this? Feel free to chuckle at my stupidity, and thanks in advance for any advise.

[Matt@RFR]

Your breather/pcv are correct. The only time I've seen front or rear main seals fail is under 25" or more of vacuum. Opposite forces, but you can see it takes quite a bit for the seals to fail. Generally you'll have a valve cover/pan gasket fail before the front or rear main.

My guess is that your "pro" shop installed the seals backwards, or just generally fubar'd the installation.

[LowBuckX]

Ill have to say the rear main is not installed wrong.. ive seen that happen and its not pritty. Oil gushes and sprays out. Oil forces the lip onto the crank sealing it. And its almost impossible to install the front seal wrong. It wont go.

I say maybe a Bad pcv valve or insufficiant breather. Try cleaning the areas real good and running with the Grommets out and open holes.

Dont runn long or on a dirt road with them open but just see if that is the issue............... make sure you have baffled covers before you do it though...... And on that note make sure the grommets arent closing the hole off on the bottom of a baffle plate. Just make sure everything is clear under there.

[Rick Piras]

So the tube routing to carb base sounds correct? The shop said I should be running the PCV hose to the base of the air cleaner, not to the base of the carb. Their point was that by routing it the way I have it, I'm creating a closed system, and not providing adequate venting in the crankcase. Other than drilling a mounting spot into the air cleaner, it won't take much effort to re-route the hose. I was wondering if other folks have their PCV going to the carb base or not.....
Thanks again.

[Travis B]

So the tube routing to carb base sounds correct? The shop said I should be running the PCV hose to the base of the air cleaner, not to the base of the carb. Their point was that by routing it the way I have it, I'm creating a closed system, and not providing adequate venting in the crankcase. Other than drilling a mounting spot into the air cleaner, it won't take much effort to re-route the hose. I was wondering if other folks have their PCV going to the carb base or not.....
Thanks again.


I have never heard that I have always ran mine the exact way you are describing! I have also tried two breathers and no pcv and that does not work....! Sounds like a bad pcv or something!

[Matt@RFR]

Again, the way you have the pcv system is correct. It's not a closed system because the pcv has a clear path out the exhaust.

[Rick Piras]

Thanks for the help guys. I was looking for a sanity check in a world gone mad.....

Rick

[streetk14]

Like the others have said, you DO have your PCV system correct. The port on the carb is designed to be used with a PCV system. If the oil leak is in fact being caused by excessive crankcase pressure, then running the hose to the air cleaner base will only make the problem worse. Either the shop doesn't really know what they are talking about, or they are trying to place the oil leak blame on something (or someone) else. Good luck,
Andy

[zbugger]

I've seen engines leak from the crank seals when new because of improper intallation before. It's mainly cause by dry wear. I've usually dabbed a little coating of oil on it before installing the seal.

The PCV is routed correctly. The reason it's called a closed system that way is because it isn't being released directly into the atmosphere. To make it a true closed system, run the PCV as you have it, but run a tube from the other side's breather to the base of the air cleaner. That way all the fumes run through the motor and get burned up. If you didn't have any vents like that, the valve cover gaskets, intake askets, and front and rear main seals would blow out in a heartbeat.

I think that the guys at that shop telling you that crap really don't know proper airflow through an engine.

[paul67]

I am sure I have seen somewhere the vents go into the exhaust and this is on race engines.
paul67

[Rubes]

I agreee that PCV connection is correct. On one of my motors I had a rear main leak (rope seal) so I replaced it...still leaked!! Replaced it again with a Viton seal...WAAYYY worse!! WTF?? Tore the motor down to find a broken piston ring, just a small chip off the corrner. Obviouse blowby causing pressure in the crank case. Reassembled the motor again with a Viton seal (a new one)...yep you guessed it...still leaked (pretty bad) :hand: . Bottom line, what I found was that the groove in the block/cap for the rear seal was off center from the crank centerline by 0.030" - 0.040". The rope seal would probably have sealed this fine, if it wasnt for the broken ring. But the viton seal wasnt even touching the crank!!!

Rubes