replacing valve stem "O" rings

[supernaut]

I'm getting ready to replace the valve stem seals on my 75 k5 350 cid and wanted to bounce my diagnosis off the forum here.

Some of the plugs get oil fouled within a few hundred to a few thousand miles of new plugs being put in. No exhaust smoke during drive, deceleration, or on start up. I figure I am getting oil leakdown through the valve guides, not past my piston rings.

150,000 miles on engine, no knocks or anything. oil pressure fine. not tons of power, but certainly not as whipped as i would expect it to be. just hoping to squeeze another 10-20 thousand moderately trouble free miles out of it so i can buy some higher priority things before i save for a rebuild.

 

[diesel4me]

might not be seals...

If you get no "Puff" on startup,its probably not the valve stem seals--if they were gone you'd get a cloud of blue smoke every time you start it(especially first start after sitting overnight),or coast downhill and downshift it....My 305 puffs every time I start it,but it never fouled a plug(yet!)--so I dont plan on changing the seals on the valve stems anythime soon,if ever! (a little oil is GOOD for the cylinders--no "dry starts"! )..

I'd do a compression test--it could be the rings or piston wear letting oil sneak by and foul the plugs..usually if its bad enough to foul the plugs,you can see at least a little blue smoke from the exhaust...your PCV valve might be not working right,and letting pressure build up in the crankcase,that will make plugs foul quickly..

Ever see oil in the air cleaner housing??--if so,its probably bad rings or the PCV system...you could use "non foulers" on the plugs that foul to squeeze out a few thousand more miles without fixing anything,and add some "Lucas" oil stabilizer to thicken up the oil some to slow down the oil fouling..

 

[supernaut]

Thanks for the suggestions. i'll pop in a new pcv for kicks and take a serious look at my ignition system. Maybe I missed something there.

 

[diesel4me]

Some suggestions..

Try a new PCV valve ,and make sure its hose isn't plugged up,or collapsing under vacuum,rendering it inoperative--also make sure its vacuum source is not plugged with carbon where the hose connects to the carb or intake,and it has good suction while the engine is idling..the breather has to be clean too ,in the opposite valve cover..

Sometimes excessive fuel will foul plugs and make them look like oil did it..a choke that sticks or does not fully open will cause this..makes it drink gas at an alarming rate too!..weak spark can cause plug fouling too,usually caused by old plug wires or a weak coil..dirty air filter can do the same thing..

A "leakdown" yest is more accurate than a compression test when looking for excessive oil consumption reasons..put compressed air into each cylinder using an air hose fitting in the spark plug hole and turn the engine to TDC on that particilar cylinder and listen for leakeage out the intake,exhaust,or the valve covers...leakage from the intake or exhaust is from bad valves,the crankcase blow by shows up at the valve covers if the pistons and rings are leaking...NO engine is 100% airtight,so dont condemm it too easily..SOME leakage is normal..If your losing more than a quart of oil every 500 miles or less,it needs rebuilding most likely...good luck..

 

[supernaut]

I'm not sure i've got vacuum applied to the pcv, i'll have to check that today. definitely not burning a quart every 500. oil leaking down from my driver's side valve cover (didn't replace that one, AC in the way and i didn't want to deal with it) may be causing the plug wires to short out. I'll fix that.

If my pcv is truly devoid of manifold vacuum that might explain my dieseling problem that I couldn't fix for the life of me...

After this stuff i'll test the HEI unit before I do the valve seals. If I fix the problem I plan on doing the seals anyway, I've wanted to get in there and adjust the valves for awhile now. Not to mention replace the timing chain, that's a weak link i've always been burned by. then i can replace the whole oil pan gasket without cutting it where it goes under the timing chain cover.
lol crap this is starting to sound like an in frame overhaul. LOVE MY TRUCK!

I've got a carter afb carb instead of the rochester.