The Stovebolt Site Forums The Shop Area Engine Shop Smoking

I bought a 1978 Silverado brand new. It had a 350, 4 bbl carb and ran wonderfully for 27 years. Never stumbled, never idled rough, no problems...except one. Around 30,000 miles it started puffing blue smoke when started. I just lived with it. I had to rebuild it around 130,000 miles. I was disappointed as I had changed the oil every 2000 miles and had expected a much longer rebuild life. I had it rebuilt by Jasper engines and transmissions in Indiana. They pride themselves in using all new valves and seats. Well, in 3,000 miles, it was puffing blue smoke again. HAs anyone ever heard of a problem peculiar to the 1978 variety 350? I want to transplant this engine in my 1965 stepside, but I really wish I could make it stop smoking. IT only has 10,000 miles on it.

Sounds like they used the cheap Chevy o-ring style valve guide seals instead of the umbrella type.

from what I understand that is the exact reason GM went to the positive type valve stem seals.

You can go to the positive type valve stem seals and eliminate the smoke, but be sure to remove the O rings under the split locks and the sheet metal deflectors from the top of the valve springs. Otherwise you'll starve the valve guides for oil and wear them out in a hurry. There MUST be a little oil going down the valve guide to prevent dry running and galling or rapid guide wear. The smoke is caused by excessive valve oiling and oil puddling on the back of the intake valves with the engine stopped.
Jerry

I'm pretty sure they used the unmbrella type seals. I asked the salsman who sold me the rebuild and he said they did not use the GM o-ring seals, but were a step-up with the umbrella style. On a side note, I bought an '86 GMC with a 305 from my neighbor. It was puffing blue smoke too at start up. He too, had changed his oil religiously and was disappointed like I was. He had used 10W-40 oil. I switched that engine to 5W-30 and it quit smoking completely. I am thinking that "thinner" oil runs off the valve stem better at shutdown and isn't around during start up to be a problem. Does that make any sense? Oil viscosity always confuses me...

The only way to be sure is to remove the valve springs and check the stem-to-guide clearance by trying to move the valve stem back and forth. If you can see any movement at all, that's too much- - - -pull the heads and find somebody who knows how to do a valve job the right way.
Jerry