puff of smoke on startup...

[jensenstage1]

Hey guys, im trying to figure the cause of the blueish smoke upon startup, i drive an 86 c10 305/sm465. Ive removed all emissions control equipment, installed headers and 2.5" exhaust that dumps before the rear axle. Every now and again, upon startup she gives a good puff of smoke. now one mechanic says its my rings, but its not a constant smoking and the other says its my valve stems. The valve stems make sense because oil will leak down the valve shaft into the cylinder. I was just hoping some one could clarify with me what they think it is and what could be done to ensure thats what it is. Thanks Guys!

Jensen

[klaussk]

If it was from oil because of bad rings or valves it would be black smoke. blue smoke is usualy unburnt feul. And since it only happens occasionaly upon startup id say its because the engine is cold and not burning all that feul because the chock is on. I wouldnt worry about it.

[4x4orbust]

valve stems would cause the smoke at startup.  just as you said, the oil leaks past them when sitting and pools in the cylinder.
   does it only do it on a cold startup?    blue/grey smoke is oil, black smoke is unburnt fuel, white is coolant. 

[DustyRusty]

Um, it appears to me your valve guides may be worn and causing the problem.  I'm not sure changing the valve stem seals will help much if the guides are worn badly.  If your engine is not consuming a lot of oil between oil changes, I would be inclined to drive it as-is.

Rusty

[bake74]

     Does it have a slight tapping sound when you start it up ?  Then as it gets warmed up and builds pressure the tapping sound goes away.  If so could have sticky push rods or valves.