How do you burn an exhuast valve? And how poorly will the motor run if you do? Any symptoms? Thanks guys

 

I belive from it being stuck open. And you melt/deform it?

 

How do you burn a regular valve? How obv. is it when your driving that the valve is burned? I'm being told mine are burned because the heat from the manifolds? Thanks guys

 

I don't know for sure but I heard that if you have a major exaust leak you can burn your valves over time and if your timeing is way off it could also cause it. You could try a compression test on all your cylinders if you want to be sure your valves are still good. Not sure what symptoms it would show but I would guess a loss in power and gas mielage. Someone correct me if I'm wrong.

 

Yeah I will diff do a compression test sometime and check them out. I heard its like having a bad head gasket with bad valves. Not sure how true that is though.

 

My dad has an 86 jeep that has a 2.8l v6 with a 2bbl carb, and the muffler was worn out and all rusted out and if he reved it up he could get it to backfire, and he thought it was real cool so he would do it all the time, ran it till the muffler eventually blew out and fell off, he picked it off the side of the highway and kept it as a trophy, lol!. For about two years he ran it with no muffler without adjusting the carb and now it has 2 burt valves. The thing sucks, it can only go 30mph if your going down a hill in town only when its cold. If you try to floor it it bucks, most of the time you can only go 15mph, once the car warms up it just really sucks, eats gas like crazy, failed emissions, basically the car sucks at life and just sits; only gets used for getting groceries down the street...

 

Valves get burnt when they are exposed to excessive heat. Mostly when they either get stuck open or, for some other reason, not able to dissipate heat quickly enough. Most of the time it's from excessive RPM with weak springs, or an exhaust leak at the head/exhaust manifold. When a valve is off the seat, there is no where for the heat to go, but when it seats again, all the heat is instantly dissipated into the head, that's why valve jobs are so important. The seat must make as much contact as possible with the valve. When you float a valve due to the weak spring theory, the same thing happens, there is just no where for the heat to go, so it melts the valve.

An exhaust leak lets a small amount of oxygen into the port, where it combines with the heat that's already there and the unburned fuel that ALWAYS comes out of a cylinder. It oxidizes(burns) the fuel, causing excessive heat, and that screws up the valve.

As for symptoms, you will notice a roughness at idle that slowly goes away as you increase RPM. You will have poor fuel milage, a fuel smell from the exhaust and a plugged cat VERY SOON. Any knd of cylider sealing problem will show up like this.

Do a compression check, that will give you an idea of what all the cylinders are doing as far as balance. Then, if you can get a hold of one, use a leak down tester to find where the leak is going. That''l tell you if it's just going past the rings, past the intake, exhaust, or headgasket.

Be carful with a compression test alone though. We had an explorer at the shop the other day that felt like it had a dead hole, the OBD-II code was for cylinder 6. That cylinder was pumping out 110PSI while the others were doing 140PSI. Not a bad spread but definitly where the miss was coming from. You wouldn't thing that it would be as severe as it was with 110PSI of pressure, but when we did the leak-down test it had 80% leak out the exhaust. A DEFINITE problem. On a worn motor (150K+ mi.) you want to be right around 20% leak, that's normal. It almost all goes past the rings.

Anyway, hope this helps.
Jeff

 

Thanks man. Diff a big help for me

 

Something I forgot to put in the last post for ya', if you get to actually do a leak down test on the cylinders, make sure that you put each one at TDC BEFORE you test it, or you'll just get a major leak out one of the valves and end up with a false diagnosis.

Good Luck,
Jeff