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Strange vapor
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Author:  coconuteater64 [ Sat Apr 16, 2016 12:30 pm ]
Post subject:  Strange vapor
I searched but couldn't find anything about what's going on with my slant. I have an 83 van with a super six, and it's had a problem with an intermittent miss under load lately. I put in new plugs, wires, cap, etc. but no changes. The miss comes and goes. But that's not what I'm concerned about the most.

I had changed the head gasket about 20K miles ago and the valves looked good, and other than the head and pushrods being really sludged I didn't see anything unusual. After the gasket change it ran great. Today when I changed the valve cover gasket I cranked it up with the cover off just for gits and shiggles. I noticed a lot of vapor coming up from the lifter Valley around the #5 cylinder, particularly around the exhaust pushrod. No other cylinder had this, just this one. Best I can tell it's oil vapor, and was present as soon as I started it up. It didn't get any worse when it was warmed up.

I've never seen oil vapor come up from the lifter area before, not just from one spot. It still has the intermittent miss under load; sometimes bad, sometimes minor and goes away. Any ideas?
Author:  sandy in BC [ Sat Apr 16, 2016 1:16 pm ]
Post subject: 
exhaust valve seal
Author:  coconuteater64 [ Sat Apr 16, 2016 1:45 pm ]
Post subject: 
Quote:
exhaust valve seal
But I thought valve guides would cause exhaust smoke?
Author:  SlantSixDan [ Sat Apr 16, 2016 4:06 pm ]
Post subject: 
Quote:
exhaust valve seal
I don't agree. The valve stem seals' job is to prevent too much oil reaching the valve stem. It's not there and not capable to hold in vapour going the other direction (up the valve stem), which in any event could only happen with very severely worn valve guides.

Anyhow, as I understand it this vapour is coming up around the pushrod, not around the valve itself. That suggests larger issues, like faulty rings or a cracked piston back there.
Author:  Mikedodge [ Sat Apr 16, 2016 5:48 pm ]
Post subject:  Vapors
Im with Dan it sounds like blowby. With the valve cover on angine hot idling with pcv valve in how much is coming out then a little brake torque and see how much is coming iut. Check at rear valve cover vent
Author:  coconuteater64 [ Sat Apr 16, 2016 7:09 pm ]
Post subject:  Re: Vapors
Quote:
Im with Dan it sounds like blowby. With the valve cover on angine hot idling with pcv valve in how much is coming out then a little brake torque and see how much is coming iut. Check at rear valve cover vent
Quite a bit is coming out, actually. At idle on a cold engine it's noticeable, but around 1500 RPM it seems to be a lot less. At 2500 RPM it's significant. I didn't rev it any higher because it started slinging oil at that point.

This started all of a sudden, but it did sit unused for over a year before being forced into daily service. I think maybe Dan is right, a ring has packed it in. But the spark plug wasn't oily, so maybe the oil control ring is doing its job.
Author:  coconuteater64 [ Sun Apr 17, 2016 9:17 am ]
Post subject: 
So to satisfy my curiosity, I tried a little test. I cranked it up with the vent disconnected, and there was the oil mist. I let it run up to operating temperature; no change in the amount of oil mist between warm or cold. When I pulled the #5 spark plug the mist stopped. So it's definitely that cylinder causing the problem. Curiously there is no smoke out the tail pipe.

I'm not sure if it's a stuck ring, cracked piston, cracked block, or any combination of those. Unfortunately, I won't have time to work on it the rest of the weekend, but I think a leak down test is next.
Author:  SlantSixDan [ Sun Apr 17, 2016 6:13 pm ]
Post subject: 
Y'already did one o' those: Yup, it's a-leakin' down. »ducking«
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