Crankcase Breather & Dipstick Blowout?

[maytag]

Engine has to vent both pressure which gets past rings and pumping pressure/vacuum created with pistons pushing up and down. Hence big hose from crankcase to air filter. Air does indeed flow both ways, but generally out of crankcase due to some blowby.

Under what conditions would you see air flowing INTO the motor through the breather?

[BEEK]

never would air flow into the breather, engine builders dream of a vacuum in the crank case. in dry sump engines the scavange sections of the pump on a 4 stage pump will create a vacuum. this does promote better ring seal too and make more power

[RRoller123]

On the FI engines, is there a regular part that should be checked and cleaned? I haven't looked for any of this sort of thing.

Pete

[BEEK]

not really, the cyclonic trap, can build up with sludge, not that modern oils are used, that should not be a problem

[mgbgtn]

On my 73 there is a wire filter built into the piece of pipe coming out of the air filter were the breather hose attaches and if this gets blugged with oil it will not let the engine breath and cause the crankcase to build up pressure and give the results that you are having.

[majicwrench]

When the engine cools down, guess what, air flows into the engine from the breather. When you decelllerate without depressing clutch, the pressure in crankcase drops dramaticly, and air flows into the engine from the breather.
Keith

[maytag]

When the engine cools down, guess what, air flows into the engine from the breather. When you decelllerate without depressing clutch, the pressure in crankcase drops dramaticly, and air flows into the engine from the breather.
Keith

Disagree.
pressure may indeed drop, but it is still pressure nonetheless. It is not a vacuum.

I can imagine NO scenario where air would be moving INTO the crankcase through the breather. Beek is right, that engine-builders dream of vacuum in the crankcase. Some methods of artificially inducing vacuum have existed for years (60 or more), but even under those situations, you are drawing air OUT of the crankcase, in order to create a vacuum.

Air does not travel into the crankcase through the breather.

[majicwrench]

I did not say it is a vacuum. And a vacuum is simply LESS pressure than atmospheric (sp?). On decell--engine braking-- you get a drop in pressure (vacuum) in the cylinders, so instead of blowby, you get the opposite effect, which is why old worn out engines smoke so bad on decell, because they are sucking fumes-oil-air out of the crankcase and into the combustion chambers.
Certainly air goes both ways.
Keith

[So Cal Mark]

you can't keep pumping air out of the crankcase without a source of air in. There is (or should be) a flame trap in the breather hose that needs regular maintenance

[maytag]

I did not say it is a vacuum. And a vacuum is simply LESS pressure than atmospheric (sp?). On decell--engine braking-- you get a drop in pressure (vacuum) in the cylinders, so instead of blowby, you get the opposite effect, which is why old worn out engines smoke so bad on decell, because they are sucking fumes-oil-air out of the crankcase and into the combustion chambers.
Certainly air goes both ways.
Keith

no, the smoke on "decell" is from a pcv (or other crankcase venting system) blowing that higher pressure into the intake tract, and pushing it through combustion. if you don't believe me, try finding a car that does that, and then disconnect the PCV from the air-cleaner. you'll see I'm right.

no, air does not go both ways. And I'm not sure why you would want it to?

[BEEK]

piston rings to not make a total seal, even with "total seal" gapless rings. on ever compression stroke a minute amount of compression does pass the ring package and escapes into the crank case. the pistons displace the same amount of air on the backside of the stroke. theoretically as one goes down the others go up and no difference in volume occurs. but the crankcase has positive pressure at all times,during a hard closed throttle deceleration, the amount is less than full throttle acceleration. as to why worn engines smoke on deceleration, oil is passing the ring package into the combustion chamber, the throttle is closed and the point of least resistance becomes the rings. also oil is drawn past the intake valve guides too.

[mgbgtn]

Any small block chev that I have worked on allows air INTO the crankcase from a hose on the filtered side of the air filter and out of the motor through the pcv valve to the intake manifold! And yes the motor will pull oil up through the rings especialy if you take your foot off the gas going down a long hill if your motor is worn.

[maytag]

it's odd to me that I take a 3-month hiatus only to return and find the same people propagating the same wrong ideas.

I guess I need a 6-month break this time.

[majicwrench]

Funny thing Maytag, I feel the same way!!! Pretty much took the whole winter "off". Guess we will just have to agree to disagree, and enjoy the banter.
Keith

[timinator]

no, the smoke on "decell" is from a pcv (or other crankcase venting system) blowing that higher pressure into the intake tract, and pushing it through combustion. if you don't believe me, try finding a car that does that, and then disconnect the PCV from the air-cleaner. you'll see I'm right.

no, air does not go both ways. And I'm not sure why you would want it to?

The "smoke" is caused by oil being introduced into the combustion camber. Not from the pcv blowing higher pressure. If the air flow from the crankcase into the air cleaner is of high enough velocity it will carry oil droplets. Usually there is some sort of oil separator needed in the system as opposed to a big hose. If you don't want these oil droplets to burn in the engine don't connect the hose to the air cleaner. Us old guys call that a road draft tube. The oil just winds up everywhere except in the combustion chamber. For an engine without a pcv valve is it correct to call the system a positive crankcase ventilation? If the dipstick is blowing up from pressure in the crankcase either give the pressure a better path out of the engine or tie down the dipstick. I have noticed stock turbo charged cars have double o-rings on the dipstick where it goes into the dipstick tube to effectively lock them in place and yet they don't show blue smoke out of the tail pipe.

Maytag, glad to see you back from your self imposed exile. So many ideas propagating around here for you to enjoy.