So let me start by saying this is a 50 year old OHV motor with unknown miles. She runs *very well*, has great oil pressure and doesn't smoke out of the exhaust. However, I get a ton of blow by from the oil caps on the valve covers and from the road draft tube. I also have some hard facing going away on the cam, and oil consumption is up a bit. Is this smoke issue cause by the heads or by the rings? I thought worn rings would give me smoke out of the pipe as well. (I'm just trying to keep her alive and leave the engine in the car till its time for a complete rebuild, so my short term plan is to do the heads, timing set, cam/lifters/pushrods and an oil pump.) Any advice is appreciated... Its a '57 Pontiac 347, if that helps. Thansk! jay
you're almost at that cridical point, by the time you spent doing all the mentioned above you almost rebuilt the engine. why not spend a couple bucks more and save yourself some time by not doin stuff twice and not tryin to diag another problem after you do all that stuff. In the end you would be much happier.
if it was valve seals i think you would see it out the pipe. sounds like your getting the blow by from the rings. have you tried running thicker oil in it? like valvoline racing 60 weight or so?
Probably rings, or possibly a broken piston. Compression is getting into the crankcase. Rings will also allow oil into the combustion chamber, but if the oil control ring is still doing its job, the smoke will be minimal. Blue oil smoke from the tailpipe is usually caused by bad intake valve guides/seals. I'd do a cylinder compression test before I did anything though! What kind of car are we talking about??
You do the heads and something else will go away cuz of the increased compression...same with cam and lifters... Tear it all the way down...refresh EVERYTHING and then you won't have to do it a piece at a time...you (and it) will be better off for it...and the engine will last a long time. R-
I agree, One of my more stupid exercises was having the heads on a 110k mile SBF in a 66 vert mustang "freshened up" after I blew a head gasket, I was in college and didn't have the cash to do the bottom end. The engine ran great up until the head gasket blew, no oil use at all, I figured I could get away with the just the heads and I'd get to the bottom end during the summer. No real decking was done by the shop, just a quick 3 angle, and reused everything I could, out the door under $200. I reinstalled the heads with a new gasket set and in less than 100 miles puked the bottom end, it was so bad after the heads were installed that the dip stick tube smoked like a train stack and it ended up ruining the cam.
The compression rings are done, the oil rings are still doing their job as far as keeping oil out of the combustion chamber, but the oil rings don't do much for holding compression
Well, I’m glad I searched for this thread. I’ve got my eye on a running 394 Olds engine that smokes like crazy out of the valve covers. I had always thought it was the other way around, that the valve seals caused the pressure in the valve covers and bad rings sent oil out the tailpipe. That’s what I thought for many years so how about a little more discussion on this Here’s a photo, but it’s pretty hard to actually get a good shot of the smoke coming out of each side
You could do a leak down and know. You don't absolutely need the tool, it can be rigged if you have the right stuff around. https://www.harborfreight.com/cylinder-leak-down-tester-64918.html Mike
OK, cool, this is a complete running Olds. I’ve decided that’s the only way I’m going to buy an engine from now on, even if it needs new rings. I know it’s running, transmission goes forward and reversed and the rear end isn’t burnt out. That’s the way it was done in the olden days. Take a running car and strip out as much as possible
The area between the valve stem and the valve guide is VERY small, and would have to be severely worn in order for the valve seals to be the cause of smoke/vapor coming out of the valve covers. The "path" of smoke/vapor from the valve covers is the many different openings in the head that are exposed to crankcase pressure. These openings are the pushrod holes, oil drain back holes, etc. Bad compression rings and the accompanying "blow by" is going to be the primary reason for all that fun stuff puffing out of the valve cover vents, oil fill tube breather and road draft tube.
This seems like perfect reason to pull the plugs and get a borescope down the cylinders to check for cylinder wear or possible damage to the top of the pistons. If this is a 50 year old engine and hasn't been run frequently or regularly for an extended period it may have some rings sticking in the pistons. Some extended running with a fresh oil change may cure some or most of your problem. Might also add some Marvel Mystery Oil or similar "ring free" additive with the oil change. Rigging up a working PCV system will also make a big improvement.
@Rand Man, even if the guides were loose and had no seals, there is ambient air or vacuum in the intake ports, and exhaust pressure on the exhaust guides. The big pressures are in the combustion chambers pushing the car down the road. It getting past the rings into the interior of the engine is what you are seeing. If you think about very early engines or large powerplants, they have exposed valvetrains, but the crankcase is sealed. You wouldn't see puffs of smoke from the guides. Das Boot.
If you think about an engine running, you can picture why the air inside the crankcase is pretty turbulent even without blowby.
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