I thought black smoke is gas -- the rich, sooty unburned fuel. Bluish smoke was supposed to indicate oil burning in the combustion chamber -- as with oil getting past the valve stem seals and guides, or oil bleeding past the piston oil control rings.
Exhaust Color DiagnosisBlue/Gray Smoke:
ASE A1 Engine Repair Certification Practice Test wrote:
Q: A vehicle briefly blows bluish/gray smoke from the tailpipe only when first started in the morning. The most likely cause of this condition is:
A: A leaking valve seal will cause oil to leak into the cylinders chamber over time, usually overnight.
Blue/gray exhaust smoke is an indication of oil burning in the combustion chamber. These are possible symptoms and causes:
Valve Seals: Leaking valve seals will cause blue/gray smoke at startup because oil leaks past the seals into the cylinder after the engine shut down.
Valve Guides: Excessive clearance between the valve stem and the valve guide allows oil to leak past the gap into the cylinder.
Piston Rings: Worn or damaged piston rings will cause blow-by resulting in blue/gray smoke.
Worn Cylinder Walls: Worn cylinder walls cause blow-by resulting in blue/gray smoke.
PCV System: A stuck closed PCV valve will cause excessive crankcase pressure resulting in blue/gray smoke.Black Smoke:
Black exhaust smoke is an indication of rich fuel condition. These are possible causes:
Fuel Injectors: A leaking or dripping fuel injector will cause a rich fuel condition.
Fuel Pressure Regulator: A stuck closed fuel pressure regulator will cause a rich fuel condition.
Fuel Return: A restricted fuel return line will cause a rich fuel condition.White/Gray Smoke:
White exhaust smoke is an indication that coolant is burning in the combustion chamber (if you see this, you are not driving an air-cooled Corvair)
. These are possible causes:
Cylinder Head: A crack in the cylinder head (around the coolant jacket) will cause coolant to enter the combustion chamber.
Engine Block: A crack in the deck of an engine block near the coolant jacket will cause coolant to enter the combustion chamber.
Head Gasket: A damaged or blown head gasket will cause coolant to enter the combustion chamber resulting in white/gray smoke coming from the tailpipe. http://www.freeasestudyguides.com/exhaust-color.htmlhttp://mylist.net/archives/corvaircraft/2011/036119.html
http://www.corvair.com/user-cgi/catalog.cgi?function=goto&catalog=MAIN§ion=MAIN&page=6Part number C5857A: TEFLON INTAKE VALVE STEM SEALS-SET 6 ONLY GO ON INTAKE VALVES!!YES-WE'RE SURE!!
The Corvair Aircraft Engine Crowd wrote:
CorvAircraft> Valve Stem Seals
Rad Davis rad_davis at sent.com
Mon Apr 11 18:18:12 PDT 2011
Mark has correctly identified the reason that valve stem seals are used on Corvair cars. Simply put, they keep oil from oozing into the intake and exhaust ports when the car is parked on an incline and oil pools in the downhill rocker box.
You get a light blue puff at startup from oil down the exhaust valve stems. In extreme cases, enough oil down the intake valve stems can cause misfire due to fouled plugs on startup.
There is also the concern that car engine spend a lot of time at idle and light loads (high intake manifold vacuum), and some wear on the intake valve stems can result in a lot of oil being pulled down the intake valve stems and result in heavy restrictive carbon deposits on intake valve heads. I've seen engines like this - it does indeed happen with a granny drive cycle, bad seals, and some valve guide wear.
On the other side of the argument you have the simple fact that a tight clearance between valve and guide needs regular lubrication or it will become loose, and the stated purpose of a valve stem seal is to restrict oil flow into this space. It's a particular concern on the exhaust valves, which run much hotter and don't have the consistent strong difference in pressure to pull oil down the valve stem and keep them lubricated and cooled.
For a car, probably the ideal thing to do is break the engine in with no seals, then fit them to the intakes after break-in if you don't anticipate thrashing it enough to keep carbon off the valves. On an airplane, I can't imagine why one would run seals at all, for precisely the reason Mark mentions. In any event, there's no reason to use exhaust stem seals ever - all they prevent is a momentary puff of blue smoke on startup.
I don't call the Corvair engine the 'blue smoke six' for nothing. Accept this part of its character and be grateful it's not a radial or a two-stroke.
- Rad Davis
On 4/11/2011 7:00 AM, Mark Langford wrote:
Rodger Nicolls wrote:
Should I use the Viton valve stem seals on only the intakes or on the exhausts also?
I think conventional wisdom on aircraft engines is don't use them at all on either valve. I've never put any on my engines, and I don't "use" oil or blow it all over the place either, so apparently that works. Aircraft engines don't experience that high vacuum situation that you'd get with a car going downhill with the throttle shut, so it's not a problem in our usage. I left them off my first engine because of my VW experience...they'd just melt off and you find them in the sump at the first oil change. Conversations with William Wynne verified my belief that they were unnecessary. I cherish my valves and valve guides, and wouldn't mind a bit if they stayed better lubricated anyway...
Weight: 0 lbs 2 oz
Catalog Pages(s): 6,17(5)
Price: $ 15.05Part number C1030 (Regular): SEAL-VITON-VALVE STEM-SET 6--IF ASKED ONLY GO ON INTAKE VALVES!!-TEFLON= C5857A
Weight: 0 lbs 2 oz
Catalog Pages(s): 6,17(5)
Price: $ 11.15FROM CORVAIR UNDERGROUND - Left-click with mouse to enlarge the image...