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350 Breather Cap - options?

Dan_az80

Dan_az80

Well-known member
So I have a little blow-by coming out of the PCV hose(s) on my 260hp 350. Not much but after each day I have a dab of oil sitting on the intake that I have to wipe up and it's coming from the PCV hose.

Engine is pressure tested - everything checks out.
Oil Pressure - good across RPM range and doesn't burn oil.
Temp is good, if anything it is on the low end of the operating range - 120*.
No oil temp gauge, thinking about installing regardless.

Currently there is no breather and just elbows with the hose attached coming from the valve covers. I am thinking that installing a breather cap w/ hose hook-up will solve the problem...has anyone run into this before or used this application?
 
Yes, the "PCV" tubes are hooked up at the spark arrestor. They are "slash-cut" at the spark arrestor, and not hooked directly to it. I understand that basically any vapors that would come out of the tubes they would be sucked into the spark arrestor. The tubes are 1/8" or less away from the face of the spark arrestor.

Sorry, I left that out earlier. After looking at photos of other similar 350 Merc's from the same era, it looks to be a common set up and not bastardized....for lack of a better term. Looks like everything is a stock setup...but I have seen other spark arrestors that the tubes hook directly INTO the unit as well...
 
sounds stock...maybe clean the spark arrestor for starters.maybe just getting tired. you could look under covers and make sure oil return holes are not blocked.
 
When you said pressure tested do you mean a compression test? You could have good compression but a bit too much blow by. You can also have worn valve guides and/or calve stem seals. The exhaust going past the exhaust valve can push up and out of the worn parts and push excessive oil out of the breather rubes.
 
Compression test, yes.

I figure my tolerances are slightly loose due to the age and hours (unknown but I figure around 500). I would just rather not have to mess with it too much to get rid of a small problem...like they say, it's the little things that get to you.


Simple Green for cleaning the spark arrestor?

Thanks for the help guys!
 
Leakdown test will tell you more than a compression test. I believe kerosene is good for cleaning the arrestor but get confirmation from someone who is more experienced than me.
 
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