To PCV or not PCV is the question.

[f_inscreenname]

Hey folks. Like a lot of you already know I am building and installing a motor in my boat. It is not anything you will find in the everyday manual so you will have to bear with me.
This is the motor.

It’s a 1986 454 Mercruiser bolted up to Volvo Penta. Or what I like to call my VolCruiser.

For once I am going to run the stock valve covers. I’m tired of the aftermarket chrome covers looking like crap in a year on the other motors in the past. The only thing is with the after market you end up with a breather filler cap in one and a PCV hole in the other. Simple and I have to say I like it better then the old hose to the flame arrestor thing that most motors have and running a PVC valve has always worked out fine for me. Now though with the stock covers it has a rubber plug for the oil fill hole and PCV port in both covers. When I bought the motor a lot of that stuff was gone but there was one “PCV Valve” left in one cover. It is really just a shell of the PCV valve with no internals (a straight pipe). So now I am not sure what to do.
Should I install 2 gutted PCV valves in both covers with a “T” to join them together and then to the flame arrestor? Not really big on the hose outside the carb thing like I said before.
What about 2 PCV valves to a “T” and then to the PCV port on the back of the carb? Will that work? I guess I would have to add a breather cap if I did that?
How much crankcase ventilation does a 454 need. Does it need both PCV ports or can I install a breather cap in one side and PCV in the other?

 

[Coors]

Re: To PCV or not PCV is the question.

I bought a 88 omc 5.7, that had been rigged all to heck. I found, at auto parts store, breather caps with nipple for the pvc hoses.I soldered up 2 45 degree fittings on a 1/8 strap that bolts on top of spark arrestor. I have ventilation for the crankcase, and the vapors are sucked in by the engine and burnt, now. (all chevy breather caps fit small and big block).

 

[Coors]

Re: To PCV or not PCV is the question.

forgot- just run a hose to real close to the spark arrestor; if it doesn't hook to carb or intake vacuum; no valve needed, and it will help cut down oil leaks, from blow-by pressurization

 

[f_inscreenname]

Re: To PCV or not PCV is the question.

Do you think there would be to much vacuum on a "open line" (no PCV valve) if I was to install a fitting inside the flame arrestor before the K & N filter instead of to the outside of the flame arrestor like Merc does?

 

[Gary H NC]

Re: To PCV or not PCV is the question.

You really are not going to keep that glass fuel filter and rubber line are ya?:%

Running the line inside the flame arrestor may suck a little oil up when you get in the throttle. Those big motors really like to breath..

 

[Reel Poor]

Re: To PCV or not PCV is the question.

The Mercruiser ventilation system on that motor is what is known as a Draft Tube System. It uses the air flowing into the spark/flame arrestor to draw the fumes and pressure build up out of the crankcase. You cannot use PCV valve in this set up as it requires an open (un restricted) air flow. The Mercruiser system uses two gutted PCV looking fittings, one in each valve cover plumbed via rubber hose to the flame arrestor.

IF, you run the PCV valve system DO NOT USE TWO. One is all you need. Vented oil cap on ONE SIDE and PCV valve on the other.

More Info Here

 

[f_inscreenname]

Re: To PCV or not PCV is the question.

You really are not going to keep that glass fuel filter and rubber line are ya?:%
quote]

Oh ya, it stays. You should see the crap it catches and thats with a oil filter size, in line fuel filter (changed regularly) and a two year old PVC gas tank.. Once the riser goes on there is a bracket that holds it so it will not flop around.
The rubber fuel line is perfectly legal and its steel up to where it comes into the picture.

Running the line inside the flame arrestor may suck a little oil up when you get in the throttle. Those big motors really like to breath..

Thats what I was afraid of.

 

[Gary H NC]

Re: To PCV or not PCV is the question.

Just was wondering...Nice looking engine..8)

 

[f_inscreenname]

Re: To PCV or not PCV is the question.

Thanks.
Lots of work with this one and my bank account is holding dust.

 

[Buttanic]

Re: To PCV or not PCV is the question.

I know some will disagree but just about all automotive engines today are completely sealed with just the PCV valve connected to the intake vacuum. The oil fill cap and the dip stick are sealed. Notice how todays cars have very few oil leaks, better seals and a crankcase that runs under a vacuum is the reason. I built a 350 Chevy for my 22 foot CC and I completely sealed the crankcase, dip stick and valve covers and use a PCV to pull vacuum. It doesn't take much vacuum to do this, 5 or 6 inches will do it. So far there is not a trace of oil anywhere.
I had a Chevy 6.2 diesel truck years ago. Being diesels do not produce any vacuum it had a vacuum pump to provide vacuum for operation of the A/C controls and it also pulled 6 inches of vacuum on the crankcase. One day the engine rear seal started leaking big time. I thought I would have to replace it until I found the hose from the vacuum pump to the engine had split. I replaced it and the leak disappeared. Running a vacuum on the crankase is also quite common on racing engines.