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gatliff
User
Aug 24, 2005, 11:42 AM
Post #1 of 9
(2703 views)
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bad valve
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I am replacing the head on 4.3 the one valve has a good bite missing from it I like to know what did this and what I can I do to be sure it don't happen agrin
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DanD
Veteran
/ Moderator
Aug 24, 2005, 2:41 PM
Post #2 of 9
(2698 views)
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Intake or exhaust valve?
Canadian "EH"
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gatliff
User
Aug 24, 2005, 3:17 PM
Post #3 of 9
(2697 views)
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exh valve about a 1/8 " bite missing
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DanD
Veteran
/ Moderator
Aug 24, 2005, 5:46 PM
Post #4 of 9
(2694 views)
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It could be due to a lean running engine due to a vacuum leak or whatever electronic reason that made the engine run lean. A lean engine runs hot and I don’t mean coolant temp hot but combustion chamber temps.
Possibly a lean engine and an exhaust leak that would allow fresh cool air (oxygen) to rush in and burned out the valve.
Like what a blowtorch can do to a piece of metal when you’re going to cut it.
If the engine were run hard enough to cause the valve to turn cherry red and then the engine shut off to allow the cool oxygen rich air to rush in past an exhaust leak, the valve could be cut.
If this were the case here the “bite” you mentioned would be in the shape of a V or pie shaped piece missing.
If it’s just burnt then it’s just a mechanical fault, weak valve and or just bad luck, it’s a piece of machinery and it happens.
Dan.
Canadian "EH"
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gatliff
User
Aug 24, 2005, 6:49 PM
Post #5 of 9
(2690 views)
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Thanks the bite is like a u or v if the motor is running lean how you find the bug the motor use oil on that head bad would that do it also there no catalytic converter
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DanD
Veteran
/ Moderator
Aug 25, 2005, 3:50 AM
Post #6 of 9
(2669 views)
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Well I guess an engine that is burning a lot of oil could cause a valve to burn out if there was enough oil carbon built up to partially hold the valve open. With you saying it was burning oil it makes me want to warn you that rebuilding the cylinder heads may cause the engine to burn even more oil. That’s if the oil burning were partly due to worn piton rings.
With the rebuilt heads sealing properly on the intake stroke oil could be sucked up past the oil control ring into the combustion chamber and on power stroke combustion pressures may get past the compression rings causing excessive blow by.
How many miles are on this engine?
Dan.
Canadian "EH"
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gatliff
User
Aug 25, 2005, 10:48 AM
Post #7 of 9
(2650 views)
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I think the motor been replace before the casting # on the head was only used to 91 so the mileage is unknow the oil is from the guides on that head it fouled the plugs most on the cly with the bad valve but also on the other 2 cly on that same head a compession test show good compession on all but the one cly if anything the compession was to good 200 psi the plugs on the other head stay clean it use a qt of oil in a 100 miles the truck it self has 218,000
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DanD
Veteran
/ Moderator
Aug 25, 2005, 11:15 AM
Post #8 of 9
(2647 views)
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The way it sounds you’re doing the right thing and if it is just the guides for the oil consumption you’ll be laughing.
Do you have torque spec’s and valve adjustment sequence, if not let me know and I’ll get them for you.
Dan.
Canadian "EH"
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gatliff
User
Aug 26, 2005, 5:36 AM
Post #9 of 9
(2628 views)
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Thank you I think I set for now
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