88305tpiT/A

iTrader: (2)

I have heard of people "burning" their exhaust valves for one reason or another but I have questions.
how exactly does the metal get burned? what does this actually mean and what causes it?
I think I may have a valve mis adjusted and I hope this doesent hapen to it until I can fix it.
thanks for the enlightenment.

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88 WS6 T/A 305 TPI--
K&N,Air foil,hypertech chip, thermostat+fanswitch
free mods, dynomax catback, urethane motor+trans mounts, PST front end poly stuff, Earl's hyperflex brake lines SSM SFCs, Bilsteins very trick homemade ramair, Accel 300+ ignition system. Ported plenum, intake and heads with 1.94I valves.
Planning: Heddman 1-5/8 longtubes, NOS 150 plate, replace the "peanut"! and Eibach Sportlines.
check it out at:
http://www.geocities.com/transam617

TomP

I'm probably wrong as hell, but I assume it means the same thing as "burnt a piston"... when you burn a piston, you melt through the metal. A burned valve should be a melted valve...


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-Tom P (Hot rodded 1986 Firebird 2.8l)

Damon

Heat the metal until little chunks of it start to come off of it and it loses it's ability to form a positive seal with the valve seat.

Usual causes:

1. Running lean
2. Running too much spark advance
3. Detonation/extreme combustion temps as a result of the above 2
4. Sustained high RPM operation under any of the above 3 conditions
5. Valve misadjustment causing the valve to not fully close. Exhaust valves shed the majority of their heat through the valve seat when they are seated. If you "hang one open" by misadjustment or other valvetrain problems you will eventually burn it.

Z's r Best

I had a small pontiac once (chevy motor) that began to miss real hard when it got to 75 or 80 mph in 3rd gear. When I pulled the head off it the #3 cylinder exhaust valve had a pie shaped slice burnt right out of it. It probably was advanced timing, high rpm, etc. I ran it hard and put it up wet for several years.

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Z's r Best

RB83L69

Damon's description is pretty good. They are usually caused in a street motor by something that makes the valve not seal such as too tight adjustment, wear on the seats, crack at the seat, valve bent/warped from overheating or sudden temp change, etc. The things he listed as potential causes are more typical in a racing situation, but can occur in any hard-used engine as well.

The combustion gas spurting out past the valve will erode the metal fairly rapidly, and the result is a valve and/or seat that look as if someone took an acetylene torch to them, because what has happened is exactly the same thing. You can tell this is going on because there is almost always a "fffft" kind of sound in the exhaust each time the cylinder in question fires.

If you have a valve that is being hung open from mis-adjustment, STOP DRIVING THE CAR until you get it taken care of. You are costing yourself a much bigger repair bill by "saving money" that way, kind of like "saving money" by driving around with worn-out brakes. They don't get cheaper to fix as the damage process advances.

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"So many Mustangs, so little time..."
ICON Motorsports

88305tpiT/A

iTrader: (2)

thanks for the info, I will adjust the valves for sure today.