1960s Blow by in engine

[Bigjoe313]

I have a 66 cdv convertible with a edelbrock carb. I'm getting some oil blowing out of the vented cap on the fill tube. The pcv valve seems good and is connected to pcv port on the carb. Anything I can do or check? Besides a rebuild.

[E Masters]

Make sure all hoses and ports including pcv valve are free of buildup and clean internally.

Clean breather cap regularly

Ensure the oil used has a high flash point and that the viscosity is not too low.

[TJ Hopland]

The vacuum signal for the PCV valve seems good and strong?   I'm just wondering if there could be an issue with how this carb fits that a different gasket or adapter plate may be partially blocking a port.   

[Suntuned]

Perform a cylinder leak down test that will tell you which cylinders have the leaking piston rings,and it will also tell you if you have any leaking valves. In my case i had three pistons with a of part the top ring land missing do to detonation, before i purchased the car.

[bcroe]

In my case i had three pistons with a of part the top ring land missing due to detonation, before i purchased the car.

It is hard to believe how some owners will allow detonation
to happen and do so much damage.  Something to check on for
50s-60s purchases.  I finally gave up on any engines made
before the late 70s, I would put late 70s engines in any
earlier car to allow satifactory operation on current
unleaded.  Bruce Roe

[Jeff Rosansky CLC #28373]

Has this car been running regularly, or has it been sitting?
Out 55 had been sitting since the 90's. When we woke it up, I had significantly more oil exhaust coming out of the breather than the tailpipes..... And I mean exhaust.
Running it with Marvel's freed the rings up after a couple hundred miles.

Jeff Rosansky

[Chopper1942]

Before performing a cyl leak-down test, put your thumb over the end of the PCV that goes into the engine. If it trys to stick to your thumb, you have plenty of vacuum from the carb. Next remove the breather cap or fill cap and put your hand over the pipe/opening. Do you feel a vacuum? If not, put a shop towel in the PCV engine fitting and blow compressed air into the PCV fitting. Do you get a lot of air out of the oil fill? If so and you still have blow-by, it's time to do a cyl leak-down test. If any are over 20% leakage, you have a sealing problem in those cyliinders.