Newly Rebuilt 302 - Continuous smoke out of one pipe! Help!?!


Founding Member
Jun 29, 2000
Plymouth, MI
I finally fired up the '69's 302 today for the first time after the rebuild. Everything went as expected except for one thing - after 15 minutes of cam break in, there was still smoke coming out of the left side exhaust pipe... a lot of it. :(
The right side exhaust was clean.

The smoke was whitish gray and hung heavy in the air. It did not seem to disipate like water vapor would. It did not really smell like oil either.

What could this be?

Here's what I did to the engine:
'69 302 bored +.030, speed pro pistons, moly rings, edelbrock 7122 cam, performer RPM intake, 600 cfm carb, hand ported stock 302 heads, new valve guides, hardened seats, screw in studs, full roller rockers, etc.

I bought used long tube headers from a friend, sand blasted them and coated them with Eastwood header coating. When I started the engine the headers gave off an ungodly amount of smoke for about 5 minutes.... It eventually stopped but the smoke out of the left pipe continued. I doubt if there is any connection here....

I am running a PCV out of both valve covers during break in (as recommended by a friend) - one to the carb base and one to the intake just below the carb. Could this have something to do with it? Yea, grasping at straws - don't want to tear this thing apart again....

I assume i either have a water passage leak, a blown head gasket (there were several backfires trying to start it initially), a piston ring problem, etc....

Any suggestions would be appreciated. :confused:

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The headers smoking at startup was the paint curing on them, nothing to worry about. The smoke out of the pipe could be several things, I recently had the same problem, and my rocker arms were a little too tight, and i was running a bit rich.

Thanks for the reply.
I thought about being rich but the engine actually runs great at higher rpm's and I figure that if the mixture was too rich (and washing the cylinder walls) that it would be out of both pipes. The intake is dual plane but each side feeds two cylinders on each bank.

Something else I need to look at is that I have PCV's in both valve covers because it was suggested that there would be a lot of blow by at first. I looked down through the carb last night and I could see some oil puddled at the bottom of the intake, directly under the carb. On this intake there are ribs on the floor of the intake and the oil was sitting between them. The PCV hose I hooked up from the right valve cover actually runs down hill to the port on the intake. I took it off and it had a bit of oil in it. I will try running it again without this hose hooked up and see what happens. I had to remove the baffles from the valve covers and I wonder if the PCV is sucking a lot of oil. Again though, why would the smoke only be from one side???

I think you just hit the nail on the head. I have tried running without baffles and oil consumption increased dramatically. Just pull the PCVs out and see if it still smokes out of the tailpipe. Give it time to clear out the existing oil of course. And get some good aftermarket covers with baffles.
If that is the problem, I wonder if there is a way to decrease the oil consumption short of getting new valve covers. I polished a set of ribbed aluminum covers off an '83 GT and painted them blue between the fins so they are really sweet looking. I hate to take them off but will if I have to.

I wonder if I could use connectors and more hose, etc. to move the PCV a little upstream to reduce consumption?
Hmmm, you said whitish gray smoke? Is this a slush box (auto tranny) or a manual stick? If slush box, maybe the vacuum compensator on the tranny has a leaking diaphram allowing tranny fluid to be sucked into the intake? Or is the engine not in the car? Just a thought. Mine smoked a little today when I got on it, maybe I'll check to see if my pcv valve is stuck or dirty.
It was the second PCV I installed on the right valve cover.... I installed the PCV directly into a gromet in the valve cover. The PCV was not shielded from oil splash.
Spark plug in #7 was soaked with oil. The port the PCV was hooked to on the intake aperantly dumped all the oil down the #7 runner.

I cleaned the plug and removed the second PCV and the smoke is gone.

Thank God it was something simple :D

keep in mind that a PCV system needs to allow for intake and exhaust. By hooking two pcv valves to the engine and a vacuum source to both, you are trying to suck all the vapors out of the car without letting any air in. Vapors in an engine are normal and going to those lengths to suck them out is not neccessary. Glad you didn't have to ditch your valve covers.
Max Power,
I thought the PCV system's main job is to improve emmissions by not letting the crank case vapors into the atmosphere unburned. A close second in importance is to keep a slight vacuum in the crank case so that oil does not ooze from gaskets.
The reason for using two two PCV's initially is that, in theory, there will be more blow by and therefore more vapors entering the crank case for the first few hundred miles (thus pressurizing the crank case). My friends 289 blew oil out the breather for awhile during break in even though he had one functioning PCV - it couldn't keep up.
I just thought I'd give it a try. To be honest, if I had executed it better (instead of putting the pcv exposed to oil splash), I don't think it would have been a problem.
I did check the crank case vacuum with one PCV in place, and it is very slight at idle but increases with engine speed. I think my rings are seating nicely.

You have the general idea of how it works, but it takes quite a bit of blow-by to have crankcase pressure equal two vacuum sources. That is a very unusual situation. Also, vacuum in the motor has no real effect of the gaskets.

What I have done in extreme blowby situations is fashion a vapor overflow where you can just dump the condensed oil back into the motor on occasion, or a system with a fuel filter in the oil cap. Pointed upwards, the fuel filter collect the oil from the vapor and it drains back into the engine of its own.

In most cases, that level of blowby is unusual.
Crank case vaccum helps your rings seal better which translates into more power. You can actually buy crankcase vaccum pumps.

You could use baffled grommets in your valve covers oz. its a gromit closed in on the bottem that u have to cut a small hole into. My tall baffleless valve covers came with instructions to do this.
Thanks for the replies - that's good information to have. Based on what I saw last night, I don't need the second PCV. If I start to dump oil out of the breather, I'll probably try to find baffled grommets.

Thanks again.
67coupe351w said:
You could use baffled grommets in your valve covers oz. its a gromit closed in on the bottem that u have to cut a small hole into. My tall baffleless valve covers came with instructions to do this.

I tried those baffled grommets in my tall baffleless valve covers. It didn't help at all, oil was still spewing out of the breathers. I eventually bought a set of chrome, tall covers with internal baffles which barely clear my roller rockers, then added one pcv valve on one cover and a breather filter inside of my aircleaner connected to the breather on the other valve cover. It was explained to me that this closed system would work better and it does for my setup. The end results is no more oil splash out of the breathers, as the pcv sucks pressure from the engine, the other breather allows fresh air into the block, or so it supposed to work.