Thread: testing for burnt valves

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I got a dollar sucked in half by my exhaust so I think I have some burnt valves. Is a leak down test the best way to determine this?
Also, is it measured over a specified time interval? because wouldn't any cylinder leak down 100% given enough time.

Burnt exaust valve or valves,I ran a 300 straight 6 for years with the burnt exaust valve.A vaccume guage will tell the story.

but I don't know what the vacuum should be without burnt valves.

if you don't have a burnt valve the gauge needle will stay study, if you have a burnt valve the needle will flicker real fast.

but wouldn't that only tell me if the burnt valve is on the intake?

Originally Posted by tcodi

but wouldn't that only tell me if the burnt valve is on the intake?

yes, then you would have to do a comp. check on ea. cylinder to find out which one was bad.

Mike thanks for that drawing. I'm sure it will help sometime down the line.

a vac. gauge can tell you a lot. i all ways run a vac. gauge in the dash of the race cars i built.

yeah I wish I had one inside my car, I couldn't get a vacuum gauge in the style of the rest of my gauges though.

ok, used a leak down tester last night and every cylinder came out around 20%, +/- 5 or so. On each one I could detect a sound if I put my ear to the exhaust pipe, it was faint as hell so I don't know if it was something else I was hearing.

Originally Posted by tcodi

ok, used a leak down tester last night and every cylinder came out around 20%, +/- 5 or so. On each one I could detect a sound if I put my ear to the exhaust pipe, it was faint as hell so I don't know if it was something else I was hearing.

sounds normal to me. did you use a vac. gauge?

no, I haven't run it yet with a vacuum gauge cause I don't have one, but I'm going to get one. Some things are still a little sketchy, like if I'm on the throttle real hard and then have to shift I sometimes get a pop out the exhaust. After taking all the plugs out last night I see that they are looking lean, which I don't understand because when I was warming it up before doing the test it was burning my eyes.

you can have a rich idle and a lean WOT. 2 dif. parts of the carb. what kind of carb. do you have?

"but wouldn't that only tell me if the burnt valve is on the intake?"
this is a ? you had before and no one answered it. this would tell you the burnt valve was on the exhaust, not the intake. if the intake valve was leaking then you would hear comp. blowing back up through the carb.

Originally Posted by lt1s10

a vac. gauge can tell you a lot. i all ways run a vac. gauge in the dash of the race cars i built.

thats one thing i love about the after market restomod gauge cluster i bought for my mustang, it looks like the factory one but they added numbers, a tac, and a vac/boost gauge.... so helpful

Originally Posted by thesals

thats one thing i love about the after market restomod gauge cluster i bought for my mustang, it looks like the factory one but they added numbers, a tac, and a vac/boost gauge.... so helpful

the gauge they put on some cars to help you with your gas mileage was a vac. gauge. light throttle good vac. WOT low vac. and if you watched the gauge you wouldn't mash the throttle as hard when taking off.