Do I need a PVC on the valve cover??

[sergioy]

I am in the process of replacing my flame arrestor, my old one is really banged up. But i've never had a pvc valve on the valve cover, jsut a big ol hole on top of it. So I called the local marine repair shop and inquired about getting one from them, so I asked them about weather or not I would also need to get a pvc valve put on there while I was doing, and the mechanic my motor did not need one.<br /><br />I know I am carrying on with out telling you what I have. It is a 1975 Mark Twain with a 165 hp stait 6. I purchased the boat from an individual in '03, and had always wondered as to the hole on top of the valve cover. Its got a rubber deal around the hole, but you can look into it and see the valves and all. Plus I get some oir on top of the dog house (on the inside), nothing bad though.<br /><br />So do I need a pvc valve, or just an elbow as stated by the mechanic? And thanks in advance for your input.

 

[trog100]

Re: Do I need a PVC on the valve cover??

an elbow would do.. just get rid of the hole..<br /><br />trog100

 

[NYMINUTE]

Re: Do I need a PVC on the valve cover??

The cost is minimal, I would retain it.

 

[sergioy]

Re: Do I need a PVC on the valve cover??

You mean retain the PVC, or the elbow?

 

[Bondo]

Re: Do I need a PVC on the valve cover??

There Is No PCV,.....<br /><br />It's Just a Crankcase Vent........<br /><br />Plumb it to the Flame Arrester,.... Just like It Was..............<br /><br />There's No Vacuum on that line, like there Would be on a Car..... a PCV would Block the Vent............

 

[craze1cars]

Re: Do I need a PVC on the valve cover??

I found this an interesting little thread, I too wondered about why there was no PCV valve on my boat, but just an elbow/hose leading to the flame arrestor. I thought something might be missing but apparently not.<br /><br />Not to nit-pik here, but it is PCV, not PVC. "Positive Crankcase Ventilation valve". PVC is a a good plastic waste plumbing material for a house. Have a happy day!

 

[sergioy]

Re: Do I need a PVC on the valve cover??

Thank you gentelmen for clearing that up for me. Once again, your advice has proven invaluable to me.

 

[Boomyal]

Re: Do I need a PVC on the valve cover??

I think you would only need a PCV valve if the hose was routed to a fitting at the base of the carb. That's the way my 302 is.

 

[QC]

Re: Do I need a PVC on the valve cover??

A couple of quick notes about PCV. As the crazy one notes, the P is for positive. The positive part is that when routed to the intake air stream there is a vaccuum on the little hose causing "positive" evacuation of the crankcase fumes (AKA blowby). What you have now is basically passive crankcase ventilation: the blowby just comes out of the hole. The V part (valve) is that there is usually some sort of thingee to knock any oil out that slpashes up there and let's it drip back into the engine. On automotive engines the PCV is really a smog device as it prevents the blowby from venting to atmoshpere. On marine engines it is more of a cleanliness and safety thing. Who wants that crap swirling around under your engine cover? Most diesel trucks just route them out the bottom of the truck which you can see anytime you walk by one idling.

 

[trog100]

Re: Do I need a PVC on the valve cover??

if an engine is in good condition there isnt supposed to be any blow-by.. with cars from the same era as boat engines there used to be an elbow coming off the valve lifter cover plates down on the side of the engine block.. this usually had a length of steel piping going down to the bottom of the engine.. the top elbow on the valve cover used to just go into the air cleaner somehow.. on some fords it used to just vent thru the oil filler cap..<br /><br />air was supposed to enter at the bottom and pass out thru the top into the air cleaner or filler cap on the cheapskate fords.. a simple flow of air thru the crankcase or ventilation in other words..<br /><br />course given a bit of use (bore wear) and the inevitable (blow-by) the crankcase got pressurized and fumes ended up blowing out the bottom as well as those that went unnoticed into the aircleaner<br /><br />they aint supposed to thow.. the crancase isnt supposed to be pressurized by blow-by.. air is supposed to come in thru the bottom not fumes go out..<br /><br />i have known folks with diesel "smokers" stick a long length of rubber hose on the crankcase vent pipe and take it right out to the rear of the vehicle.. he he <br /><br />i think with modern emission control engines.. no part of the crankcase is allowed to vent to atmosphere.. its an enclosed system.. hence the need for valves of some kind.. to be honest i aint entirley clear just how a modern enclosed crankcase gets it ventilation.. never had need to find out.. <br /><br />trog100 <br /><br />_

 

[rodbolt]

Re: Do I need a PVC on the valve cover??

trog<br /> they get them the same as alwyas. usually outside air is pulled from the aircleaner assy through a filter to the rocker cover most times, from there the air does what air does and the pcv valve is just an air metering device, its spring loaded to assist valve movement. if it clogs the engine wont vent as well and will run rich. if it sticks wide open it will run lean at idle. at or near WOT its not doing much anyway so most boats dont run one. wont do much even if they did. I ran one on my 455 olds cause inspection said it had to be there but the eninge vacum at idle was so weak all it mostly did was rattle in its housing at idle. I remember well the old down draft tubes. the chevy 265,283 and some 327's had them. dang things would clog and the only way to clear it was pull the intake. but some vehicles like my 61 studebaker just ran a tube with some fiber materiel in it and blew the waste gas out. until I had to get it certified in CA. then I had to install a vapor recovery kit. kit cost 260 dollars in 1978 and I made my own from jubkyard parts for 20. cousre I was working at the yard.<br /> watersurge<br /> if your application never ran it its more trouble than its worth to try to install it. may mean some calibration changes to the carb and above 3500 or so the air moving past the flame arrestor will suck any vapors back down the intake.

 

[QC]

Re: Do I need a PVC on the valve cover??

I am not clear how engines get air into the crankcase either, but if you think about it the air amount would only stay static with the increases again coming from blow-by. ALL engines have some blow-by. There has not been a ring pack made that can completely eliminate it. Usually worse at idle too as the manufacturers use slightly tapered rings that increase sealing effect under combustion pressure. Also, Heavy-duty turbo diesel engines are still allowed to vent the crankcase to atmosphere. Most of them do have a long hose that extends to just below the oil pan. They are cut off at an angle and faced backwards to get a slight vacuum as the truck goes down the road. All vehicle engines will have to have closed crankcase ventilation in 2007. Sorry I have made this into a vehicle discussion. My prop blows-by every once in a while though . . .

 

[trog100]

Re: Do I need a PVC on the valve cover??

Quietcat.. not sure as i have ever seem an engine that didnt have some blow-by either.. i recon my comment was based more on the theory than the reality.. he he<br /><br />trog100

 

[QC]

Re: Do I need a PVC on the valve cover??

Rog, trog.