Ask Away! with Jeff Smith: A Possible Cause (& Solution) for Excessive Tailpipe Smoke from a Recently-Revived Engine

My question regards a 1964 Chevy 327/300 HP engine in a 1957 Chevy. I was asked to get the engine running—it had been sitting since 1973 but was only supposed to have about 60,000 miles on it. I did the usual oil in the cylinders and let it sit a week then turned it by hand. I checked the fluids, installed a new battery, filed the points, and within 20 minutes it was running surprisingly well.

During the restoration, I removed the intake to look inside and I was surprised to see it was somewhat clean. On reassembly we added a new Edelbrock 1406 carburetor and updated to an HEI. The car runs great—but in the first drive the exhaust smoke was pretty bad. We did a quick compression check with 150psi across the board. A second test drive about 100 miles the smoking did not improve.

After the drive we noticed oil level was down two quarts and it was not leaking. I’m thinking I might not have a good seal on the bottom of the intake to the cylinder heads. This engine has the old Edelbrock intake that has the oil filler tube on front and there’s blow-by out of that tube. I’ve checked just about everything else. I might drop the oil pan and see if there are any broken rings or something else. It’s such a good running engine I don’t want to replace it unless it’s really something catastrophic!

Here’s my take on this. Yes, it might be leaking from the bottom side of the intake but more likely the rings are stuck in place. While the compression test shows it is sealing, the oil ring and perhaps the second ring are probably stuck from sitting so long.

I would suggest mixing a quart of automatic transmission fluid (ATF) with the engine oil and try running the engine at short bursts at wide open throttle but not necessarily high engine speed—keep it under 5,000 rpm. Hopefully several attempts at this will free up the rings and oil control will come back.

Many years ago, we had a junkyard 302 Ford on the dyno that had been pulled from a wrecked Fox Body Mustang that had been sitting for several years. It smoked badly on first running and had serious blow-by with huge clouds of breather fog. It was really bad. But after about five dyno pulls, all the rings began to break free and began to do their job again. 

If you notice that this ATF trick helps, you may have to change the oil and again use a quart of ATF to help break this carbon that is holding the rings in place. ATF is high detergent oil and will help loosen the carbon—but it will also instantly get dirty which is why you will need to change the oil and filter at least twice.

After trying the ATF trick, you will be able to tell if the engine is beginning to come around if the blow-by out of the oil filler tube is reduced. If not, then likely you will have to pull the engine apart and do a complete rebuild with new rings and bearings. That is more work, but it is the best solution. 

Some people will recommend that Seafoam internal engine cleaner and you can try that as well instead of ATF—but I’ve seen the AFT trick work in the past.