Got a modified (lump port head with 1.94I, 1.6E valves, Offy intake and Edelbrock 600 CFM carb, HEI) '71 292 Chevy 6 that's blowing some blue smoke out the tailpipe when I either A:let of the throttle after having kept my foot in it, or B: if I'm in gear and letting the engine slow down the car (e.g., highway speed and foot off the throttle) for longer than about 20 seconds. Seems to me both situations would be high manifold vacuum...so maybe I'm just pulling oil in through the PCV valves (yes, I have two)? Any other thoughts? Thanks in advance for any light shed.
4 votes for guides!! If money is tight just put a set of umbrellas on it to get along till you can pull the head and fix it right>>>>.
Here's another thing- If it is even worse after a bit of high revving, then there could be poor oil drainage back down to the engine, causing a lot of oil pooling in the valve cover and making a great opportunity for the high vacuum to slurp lots of oil thru the intake valve guides which may be submerged in oil puddles. If you decide to pull the head off for freshening up, I would be curious to know how much buildup there is on the backs of the intake valves. You might want to look into cleaning the oil return holes, and deburring + cleaning the oil return pathways to keep down any oil puddles. I agree that some new umbrellas may help for a quick-fix. While you're at it, run a bottle brush thru the return p***ages for draining. For a permanent fix- You may be OK with umbrella seals on the exhaust valves, but if you take the head off I would insist on some positive seals (the kind that requires slight valve guide machining) for the intakes since they have to deal with high vacuum trying to **** in more oil.
Yeah, you don't need 2. You need one, and a breather at the opposite end of the valve cover to create a pull-thru that will effectively move the crankcase air. good luck
Thanks for all the responses. I'm bummed since the head has less than 3000 miles on it - had a kid at Wyotech do all the machine work. With the consensus on the board, I'm considering that once this season is done, taking the head to a local engine builder and having them do valve guides and check the other work. I know the rings are all good since the engine didn't even make a puff with the stock head (which I can't put back on since the exhaust valve seat on #5 is recessed). I'll check those oil drain holes and get a breather on the valve cover for the interim.
Try plugging the vacuum supply temporarily to the PCVs to see if it still smokes out of the tail pipe. Give it a chance for the cylinders to clean out. If it improves try it with just one PCV valve. I can see no reason to have 2 PCV valves. Since it's obviously not a stock set up did you provide good baffling under the PCV valves to prevent oil spray from being ****ed into the intake? I have a friend with the same problem on a new engine with a PCV valve plugged into a hole in the valve cover that has no baffling under it. He's trying to retrofit a baffle similar to what the factory supplied where they used a PCV valve.
If you have 2 pcvs and no breather then it's pulling oil past the seals under high vacuum (deceleration). Unless the kid at Wyo did the 2 PCV thing, he shouldn't bear any blame yet. Folklore says it's possible to jack up a valve seal with too much crankcase vacuum, but have never seen it personally. Good luck.
It's a stock Chevy valve cover and the baffles used are rectangular tubes that get down pretty close to the top of the cyliner head. I'll get a breather on there and see if it helps at all.
The 2 PCV's are there since that's what was on the engine when I yanked it out of the 71 truck it was running in.
I didn't notice the part about PVCs. I don't know how I missed that. Plug them up for a while and see if it goes away. If that cures it, then you were ****ing oil vapors much too fast. You also have to be careful about WHERE you pull out the crankcase fumes. You don't want to pull out an oil cloud, you want to pull out the "old air" from a place where the oil cloud had a chance to "drop out" first, and just pull out the g***es only. If you pull out the fumes too fast, you can take the oil cloud with it.
UPDATE June 2 Got a breather installed at the rear of the valve cover (it partially covers the oil fill cap if mounted in front), and did an oil/filter change over the weekend. The oil that was in it had maybe 150 miles on it, and came out black as sin - the motor had been in a farm truck since "birth" and judging from the sludge on top of the cylinder head when I pulled it, I may be doing that again in another 150 miles. But....with the breather and new oil, most of the smoke issue is gone now. That raises another question in my head - there's a notion I heard years ago about in old motors that changing the oil in rapid-fire fashion (e.g., 3x in under 200 miles) after an engine has been sitting a long time can eliminate some smoking problems...is this just another "battery on concrete" mythconception, or legit?
Several oil changes in quick succession is a good thing in my view. ESPECIALLY if the engine has been sitting for a time. If it was an engine in storage or in a car that was parked or stored for a long time, I would conside it URGENT to drain and fill with fresh oil before the first start. A stored engine, no matter how well it was prepared, will have acids, moisture, etc that the additives in the oil may have reacted to, or combined with to eventually make the oil less protective, BUT the most important thing in my view is the amount of micro particles and grit that will be generated by cranking an engine with dry parts that haven't had a good fresh oil film in quite some time. There will be minor corrosion that gets rubbed off as the old parts seat themselves in again. The old grit that is found in even the cleanest engines will be added to by the new grit being formed by a new, minor break-in-period. I do it mostly to get rid of the old crud and circulating micro-grit that wears out engines fast. There are things that get past even good filters. Hopefully it will also get rid of some of the built up sludge. Just like cleaning out an old gas tank. Several good flush-and-rinses are better than one single fill-and-drain procedure. I believe it will save bearings and other parts from the super fast wear that you can get from dirty insides, and particles getting recirculated. I still want to recommend pulling the valve covers and running a rod or brush through the oil drain holes to make sure you don't get oil puddles on top of the heads. Slow oil draining near the valves can cause high oil consumption and sometimes smoking. The amount of sludge you find under the valve covers will tell you how much the rest of the engine will need flushing and cleaning.
I shold have been a bit clearer...the old oil that was in the motor was long gone before I ever fired it up for the first time since taking posession. I'll yank the valve cover and try your suggestion for cleaning the oil drain holes.
SLOW DOWN! I would not start reaming out drain holes right off. If there is a lot of build up in the holes, your break up all the crusty baked on oil/funk. Which in turn clog and mess your engine up. Check the holes before reaming, if they are open don't stir up trouble. If you are going to ream them out, make sure you have your oil pan off so you can clean up the mess. And keep changing your oil a bunch after. Hopefully the stirred up mess won't clog the lifters. Maybe even pull your pan again and clean after it runs a while to make sure your oil pump pickup is not getting clogged. Keep an eye on your oil pressure, look for low pressure which will indicate clogging of pickup screen. Wil www.sakowskimotors.com
X2 on SLOW DOWN Don't disturb that crud, you're asking for trouble. Bump up the oil change interval and keep an eye on the pressure gauge. If you see fluctuation you'll have to pull the pan to clear the pickup. To clean it up I would change the filter (a good $7 filter, aka purolator micronic) every thousand miles, and the oil every 2-3 thousand. Once the oil will stay decent for a couple hundred miles, that's as good as it's gonna get.
I didn't say ream it out. Who said that? The drain holes have to be open whether we like it or not. If they happen to be plugged enough to cause oil puddling and high oil burning, you have no choice but to try to lessen the problem, even if you don't like to do it. Of course you can, and SHOULD do an oil change to get rid of the loose stuff in the oil as quick as you can, but leaving a drain p***age greatly restricted or plugged is worse than NOT fixing it.
one thing else to look for, does your valve cover have baffles? some aftermarket covers that don't will **** oil on long decel (like you're talking). if you've got an oem cover, forget i said anything. it SHOULD have the baffles.
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