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pcv on 383?

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Old 09-19-2018, 11:46 AM
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Default pcv on 383?

Im having problem with my crank seal leaking on long runs around 5k plus. I have pcv on one side and breather on the other was wondering if this should be sufficient or should I run dual pc. I have a perfomer rpm airgap intake and only have one vac port and its in a runner, engine only has 20hrs on it and doesn't leak just cruising. thanks for any help
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Old 09-21-2018, 11:16 AM
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The PCV isn't working very well at WOT because there is almost no vacuum to assist pulling out excessive crankcase pressure. I had a similar issue and rigged up a crankcase evac system, but I wouldn't recommend it. Sounds like you have a little blowby or the rings are seated optimally. I have had issues with ring seal on just about every motor I've ground rings for, so that is telling me I don't know how to grind rings correctly. I had the machine shop that did all my machine work assemble the short block (partly due to time constraints, but also for the ring sealing). Haven't had any issues this year so I would have to believe I was the problem. The small diameter hose of a PCV system (3/8") likely won't relieve pressure adequately, I would go for 1/2" or 5/8" directed at the Flame Arrestor (another story), or just open K&N type breathers in both valve covers.
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Old 09-21-2018, 11:33 AM
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thanks for the answer if I get a chance to go out this weekend ill try two half inch hoses to the flame arrestor I have on k&n breather on one side now if somebody around here has one I might give that a try too.. btw I also ground my own rings which could be part of the problem hopefully not.
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Old 09-21-2018, 12:26 PM
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Sounds like you have a crank seal issue and not a PCV issue. You said you have a breather on one side and PCV on the other. I have that on every motor I have because I don't like oily air going through my breather/FA and then down the throat of the carb. It comes in at the base of the carb and gets sprayed with fuel on its way to a cylinder. Much cleaner imho.
If your motor was over pressured oil wise you would be blowing oil out your dipstick and such. The valve cover breather prevents any pressure from building in the motor. Ask anyone who didn't make sure that little tab under a new chrome valve cover breather wasn't open and blew oil all over the place on their first run. Its basically an open air system but the PCV valve just pulls enough (at lower rpm's) to draw the oily air or blow by to the carb and would never create a real vacuum in the motor to prevent oil leaks because of the breather. Its basically like putting a box fan in a window on one side of the room and opening a window on the other side. It just pulls a draft.
I would try some Marvel Mystery oil to see if I could get it to re-seal. I've seen that stuff do some amazing things and I've saw it do nothing at all also so.... Still use it in everything I own though.
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Old 09-21-2018, 11:35 PM
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I would do Vacuum testing and see what the numbers are. You might possible have low compression numbers from not good internal sealing of the rings and or the valve to seats or however. Compression test and or leak down Im sure would not hurt to do. either. Maybe improper breakin of the your rebuilt engine could also cause not so great sealing ?? What motor oil did you use for breakin and did you change it after a couple of hours of run time ?

Last edited by BUP; 09-21-2018 at 11:38 PM.
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Old 09-23-2018, 09:04 AM
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Just had a guy at our marina that had a same issue on a factory 6.2 merc, the PCV valve actually went bad and it blew a amazing amount of oil out of the dipstick...changed the valve and was fine. And NO you cannot run 2, the other side is to bring air into crankcase to be drawn out thru the PVC and into the intake or carb, now assuming you really have a true PVC and plumbed into the intake.
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Old 09-25-2018, 09:06 AM
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As far as break in goes I always run vr1 20/50 changed after 4 light hrs ran cylinder leakdown then. Almost all cylinder were close to 0 leakdown. heads are new afr's with new afr iconel valves so they should be good. I was going to check it this weekend but I had I noise I wanted to find at idle first I found it top half of alpha is blown so its new outdrive time for now I did order new pcv and another breather to try things out once I get another drive hopefully this week or next week
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Old 09-25-2018, 10:07 AM
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Originally Posted by ezstriper View Post
Just had a guy at our marina that had a same issue on a factory 6.2 merc, the PCV valve actually went bad and it blew a amazing amount of oil out of the dipstick...changed the valve and was fine. And NO you cannot run 2, the other side is to bring air into crankcase to be drawn out thru the PVC and into the intake or carb, now assuming you really have a true PVC and plumbed into the intake.
You can run 2 breathers on one side and a pcv on the other. if you have just one hole on each valve cover may I suggest running 1 breather on each side and schit can the pcv. Rare that you need a pcv, but some need to and it seems it's those with cool engine oil temps that can't get rid of water vapor fast enough. IMHO,
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