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| Why is there crankase ventilation? http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=40679 |
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| Author: | hankdz [ Thu Feb 26, 2009 1:51 pm ] |
| Post subject: | Why is there crankase ventilation? |
I am asking the question because of the problems encountered with the CCV and EGR issues. See the following post on Jeepz.com for my recent experience http://www.jeepz.com/forum/cherokee-com ... l-egr.html. Here's the background for my question. When I was in high school in the mid-1950's my dad bought a 1930 Model A Ford two door sedan that was absolutely cherry. It had really been owned by a little old lady for over 25 years and had less than 25,000 miles on it. It became my driver while in high school and college. It was completely stock. Here's the reason for relating that story. I recall it having no crankcase ventilator. That car had a four cylinder L head engine. Later in my automobile owning lifetime, I owned a 1957 Ford sedan after college, class of 1963, so obviously the car was not new. As I recall, it had a pipe that led from the lower part of the engine, to vent the crankcase fumes. You could tell when it needed cleaning because there was a baked oil aroma about the car. It was equipped with the T-bird V8 overhead valve engine. Later someone added PCV valves to the top of the valve covers and rerouted the fumes into the air intake. So, that brings me to my questions. Is crankcase ventilation really needed? What happens to the engine if there is no ventilation as in the 1930 Ford L head engine? For instance, what damage might ensue to the CRD engine if one simply placed a plate over the hole the CCV sets over, effectively stopping the venting process with the oil returning to the crankcase? What happens to the fumes? These are questions an inquiring mind would like answered. Anyone? Thanks. Hank |
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| Author: | retmil46 [ Thu Feb 26, 2009 2:07 pm ] |
| Post subject: | |
I'd bet that Model A Ford had what was called a "breather" cap for oil fill on the valve cover - doubled as oil fill and also as a filtered vent for the blowby gases that push their way past the sealing rings on the pistons. Short answer - you DO NOT want to block off the cranckcase vent (CCV) port - there's a recent thread on here describing what happened when one gent's CCV hose was inadvertently blocked off - the pressure buildup inside the engine caused most of his oil to exit the engine thru the path of least resstance - and if there isn't a path of least resistance, it can end up blowing out various seals, which can be expensive to replace depending on which ones they are. |
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| Author: | gmctd [ Thu Feb 26, 2009 2:11 pm ] |
| Post subject: | |
Likely you're mis-remembering the A - infernal combustion engines operate as the pistons pump air - piston displacement in the cylinder area above the piston is accompanied by equal but opposite piston displacement in the cylinder area below the piston - thus, the crankcase breathes just like the intake - additionally, piston rings must be gapped to a minimum clearance to allow thermal expansion - that minimal gap allows some high-pressure, high-temperature combustion gasses to seep past and into the sealed crankcase\sump area - the greater the engine wear, the greater the seepage - it will vent in that event - 'nuther words, pumping displacement and blowby will of necessity create it's own vent in a crankcase without engineered-in vent, usually around the crankshaft seals, with resultant total loss of sump oil - minimally, the dipstick will quickly eject itself thru the hood - don't believe it? - crank yer lawnmower, place a finger near the breather port on that small one-cylinder artifice - or, just pop the oil-fill cap off, feel the rush................ |
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| Author: | geordi [ Thu Feb 26, 2009 3:27 pm ] |
| Post subject: | |
Yea, open the oil cap and feel the rush... Of oil spraying all over you. Don't open that cap with the engine running, you will regret it. Don't ask me how I know. |
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| Author: | onthehunt [ Thu Feb 26, 2009 8:53 pm ] |
| Post subject: | |
Usually just pops the oil dipstick out a little and then blows all the oil out the tube. Makes a hell of a mess. |
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| Author: | hankdz [ Fri Feb 27, 2009 10:59 am ] |
| Post subject: | |
Thanks. You are correct, the A Ford did have a breather cap. All of what everyone said makes sense. |
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| Author: | liberty2.8 [ Fri Feb 27, 2009 3:18 pm ] |
| Post subject: | |
Quote: Thanks. You are correct, the A Ford did have a breather cap. All of what everyone said makes sense.
Wow, the wheels are spinning now. I wonder if we could modify our oil fill cap to be a breathable filtration cap and disconnect and plug the ccv hoses in lieu of the provent idea? |
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| Author: | warp2diesel [ Fri Feb 27, 2009 3:22 pm ] |
| Post subject: | If you do CARB & EPA is GUNNA hunt you down |
liberty2.8 wrote: Quote: Thanks. You are correct, the A Ford did have a breather cap. All of what everyone said makes sense. Wow, the wheels are spinning now. I wonder if we could modify our oil fill cap to be a breathable filtration cap and disconnect and plug the ccv hoses in lieu of the provent idea? Has Home Land Security issued them Automatic Weapons Yet? BTW: My 46 Farmall has a breather cap and it also has overhead valves, and a high tension magneto, more advanced than the Ford Model T. 
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