corvair crankcase vent

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dick2256
Posts: 117
Joined: Wed Dec 10, 2014 10:05 am

corvair crankcase vent

Post by dick2256 »

I am using a 1964 110 hp engine on my airboat
and lately I have some white foamy looking coming out
of the vent pipe and I am wondering if that is normal
dick2256
dick2256
Posts: 117
Joined: Wed Dec 10, 2014 10:05 am

Re: corvair crankcase vent

Post by dick2256 »

using a 1964 110 hp corvair for an airboat engine
and have some white foamy oil coming out the crankcase vent pipe
Should I worry about this or is that normal
dick2256
xrotaryguy
Posts: 123
Joined: Thu Feb 27, 2014 9:18 am

Re: corvair crankcase vent

Post by xrotaryguy »

Is the oil foamy or just foam collecting inside the vent? I used to get a little foam at the top of the filler neck of rotary motors when I liven in Oregon. It was humid and chilly so the foam was caused by condensate inside the tube. It wasn't generally dangerous to the engine and not an indicator of a problem. That's just one example though.

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bbodie52
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Re: corvair crankcase vent

Post by bbodie52 »

Corvair PCV systems often get modified by owners over the years as custom air cleaners and other performance modifications are made. It is important that you inspect your PCV system to ensure that it meets the original design criteria and that the PCV valve or metered orifice is clean and serviceable. The Corvair PCV system design usually works well and does a good job of evacuating contaminating gases, which helps oil and the crankcase to remain clean. A dirty or plugged PCV system, or an excessively worn engine with bad pistons, cylinders or rings can overwhelm the PCV system, which usually shows up when oil is forced out of the dipstick tube by excessive crankcase pressure buildup. If a cylinder compression test shows the engine condition to be good, and you clean the PCV system vacuum port regularly, and if your PCV system is configured as originally designed you should be in good shape.

Corvair crankcase ventilation systems evolved over the years. From 1960-1962 the engines were fitted with a simple road draft tube...
Corvair Crankcase Ventilation (1960-1962).jpg
The road draft tube was common in most engines prior to the introduction of the Positive Crankcase Ventilation (PCV) system. It did a relatively poor job of clearing crankcase fumes and contamination from piston blowby, so engine sludge was commonly seen in the crankcase, valve cover areas, etc.

In 1963 the PCV system, using a PCV valve, was introduced. In the following years, the PCV valve was replaced by a fixed orifice, which was basically an engineered controlled vacuum leak that allowed the PCV system to draw crankcase fumes back into the intake manifold, to be reburned as they entered the combustion chamber and exited via the exhaust system. A secondary component to this system is a tube that connects to the air cleaner assembly. This allows filtered air to enter the otherwise sealed crankcase, and also permits some crankcase fumes to enter the carburetor through the filtered air intake system. The properly engineered system does a decent job of keeping engine blowby gases from entering directly into the atmosphere while evacuating those gases to be burned through the combustion process.
Crankcase Cover and Vent.jpg
PCV System Layout (1963-1965).jpg
PCV System Layout (1964-1969) Sedan-Coupe-Convertible.jpg
PCV Tube Connections.jpg
Corvair Crankcase Ventilation (1964-1969) and Turbo 1.jpg
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible
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