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Venturi’s Automotive Forum :: Auto Repair :: For The Professional :: Burnt Valve
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AuthorTopic: Burnt Valve (Read 319 times)
DanD
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Burnt Valve
« Thread Started on Jun 7, 2006, 5:05pm »		[Quote]
Hey Guy’s I thought I would show you this one.
The next time somebody asks you; will that small exhaust leak hurt anything?
Show them this picture of the exhaust valve with a nice little V sliced out of it.
I told my customer about two weeks ago that we should do something with the exhaust manifold. It’s a steal header style of manifold that had cracked at the weld where #5 cylinder tube was connected to the main body of the manifold; the tube is only about 5” long and the same away from where it connects to the cylinder head. It wasn’t making tons of noise but you wouldn’t have a problem hearing it.
He (the customer) takes the car out on the highway pulls off the road at a gas station; fills up and when he goes to leave; there’s a dead misfire in the engine. An engine by the way ran as smooth as glass the last time it was in.
He brings the car back to me to have it checked. Sure enough #5 cylinder only has 50Lbs of compression.
Here’s my theory of what happened; driving at highway speeds the exhaust valves start to glow red-hot (normal). He shuts the engine off before the valves had a chance to cool. With his luck the engine likely stopped with that valve in the open position. The crack in the manifold allowed oxygen rich air to rush into the combustion chamber; a little leftover fuel, a glowing hot exhaust valve and you have the makings of a cutting torch. Which is what I think happened; looking at that nice pie shaped cut in the valve. LOL
I know it’s not nice to laugh but what’s that old Fram TV commercial saying; “ You can pay my now or you can pay me later” Now we have to fix/weld the manifold along with doing a valve job. It’s not a good thing to tell a customer I TOLD YOU SO but I couldn’t help myself. LOL LOL LOL
Dan.


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way2old
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Re: Burnt Valve
« Reply #1 on Jun 7, 2006, 5:30pm »		[Quote]
I just about have to agree with you here Dan. I think you hit that diagnosis on the head. We had a Crovm Vic that had a bad MAF and allowed the engine to run lean and it burnt a straight cut across the top of piston that was about 3/8 of an inch across. Looked like you drew a line on it with a ruler. The other 7 cylinders had the start of the same markings. So if the customer is an old one, go ahead and told him so.
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