PDA

View Full Version : How to vent the crankcase



f_inscreenname
12-24-2005, 06:23 PM
After looking at many pictures on the board I see that everyone does it different. Some with hoses from each valve cover to the flame arrestor, a breather cap in one valve cover and a hose from the other cover to the F/A, just two breather caps in each valve cover and like my dumb ass a PCV valve in one and a breather cap in the other. I say dumb ass because I have been chasing a vacuum issue that seems to clear up when I plug the PCV port on the back of the carb.
So what do you all do???

tmdog
12-25-2005, 09:35 AM
Unless you are running a carb spacer, MP has the right idea. Last year I bought a Wilson 1" spacer and before I installed it I drilled and tapped a hole for a barb fitting. Hooked my pcv to the barb and put a breather on the opposing valve cover. I felt this is the way to evenly distribute fumes, oil, and water to all the cylinders instead of to a few. With all the experiments I did with venting a crankcase, this by far was the best and most efficient, IMO. I do use the large port on the back of carb for vacuum testing. I keep a permanent hose hooked up to the port and when not in use, plugged.

MOP
12-25-2005, 11:38 AM
Of all the marine setups the PCV valve works the best, the two hoses to the valve covers is a joke, all the two hoses do is suck out blow by as no air is supplied. Air circulation is very important, air must be allowed into the engine via a breather so it can be drawn through to pull the vapors out. The moisture trapped in the engine that does the most harm, the moisture forms acids and also in many cases rusts on internal parts.

Phil

f_inscreenname
12-25-2005, 12:28 PM
So what PCV valve do you use? Like for MP's Chevy. Do you use one for a 1975 Camaro? Or is there a special valve for a marine motor because they run at different RPM's and loads?

How true is this? I read this on a diffrent board.

"Pcv valve require high manifold vaccum to work. Marine engines are practically always under extreme loads witch reduce manifold vaccum. Therefore a pcv valve does not operate properly. So as the engine builds crankcase pressure it must be vented somewhere. To keep these gases out of the bildge they are piped to the flame arrestor where the air flow into the carb/air intake can suck them in to be burned and exhausted.
Some of the newer engines do have pcv valves but they are not equivelant to automotive design, although they look alike."

joseph m. hahnl
12-31-2005, 05:56 PM
Positive crank ventilation is only needed to keep the motor from building pressure which will bind it up and stall it. It only needs to be vented to a place where vacume exist as not to create a vacume leak and to give direction of flow for the gasses.
any method will work. There is a difference between manifold vacume and venturi vacume. Venturi vacume is more constant and doesn't drop as much as manifold .Thru the flame arrestor was designed to lubricate the carb with atomized oil as well.
The PCV Valve is a one way check valve that allows the pressure to flow in one direction.
for some reason my 350 mag does not have any PCV valves .It is wide open right into the flame arrestor. This does not seem to be a problem as the motor runs perfectly .


joe

Gearhead99
01-01-2006, 08:14 AM
The PCV is installed in an auto/tk engine in case of backfire. Since they are connected to the intake, after the carb, a backfire could ignite the fumes in the crankcase and cause one heck of a bang.

If the vent hoses are attached to the flame arrestor there is no worry of backfire explosion. The hoses are before the carb and the flame arrestor is there to do what it was designed to do.

Cuda
01-01-2006, 11:28 AM
Is punching a hole through the block or oil pan with a rod/piston considered proper ventilation?

MOP
01-01-2006, 01:11 PM
Joe "Ever hear of bad Omens?"

mattyboy
01-01-2006, 01:41 PM
Is punching a hole through the block or oil pan with a rod/piston considered proper ventilation?

Joe it is a new year you need to think
Happy thoughts

Cuda
01-01-2006, 03:30 PM
Joe it is a new year you need to think
Happy thoughts
Past performance predicts future behaviour.:embarasse

f_inscreenname
01-01-2006, 08:17 PM
Hummm....http://bestsmileys.com/clueless/1.gif