Oh mighty gurus--

Enlightenment please??---

How do you know if you have a "burnt valve"??

Hear it tossed around, mostly by drag racers, but confused by what it means & the symptoms!!
Also, what is the likelyhood of it occuring to a daily driver??

( edit )
Thank You for any education you can pass!!

 

Do a compression test, or better yet, a leakdown test, and if you have low compression and you narrow the cause down to a leaky valve, then you have a "burnt" valve.

The odds of it happening in an unabused daily driver are relatively low.

 

Years ago (mid 70's) there was a vacuum gauge that would indicate if there was a burnt valve. I am not certain if that applies to more modern engines. Never run into one.

 

Thanks Apeiron!! Easy 'nuff to remember & apply!!

jwande--Never seen that before!! TDC the cylinder, Pull vacuum from the plug hole??

 

No you just hooked the gauge up, and the scale gave an indication the valve was burnt.

 

Interesting!!

Thanks for the replies!!

 

t-top,
A vacuum gauge connected to an intake manifold vacuum port will indicate some of the problems that relate to intake valves.

A crude test that can (or not lol) reveal a burnt exhaust valve is try to hold a stiff piece of paper against your tailpipe & watch for the engine to suck it back toward the pipe.

Both tests are done w/the engine running.

Leak down tests are much more conclusive but require special tools.

 

I have heard of the paper test before. We never used the vacuum gauge for anything other than trying to determine if we had a vacuum leak. As mentioned before, I have never run into one in my 24 years of working on all types of engines - tractors, implements, cars, trucks, motorcycles, small engines, and boats.

 

Thats a good idea, I'll try that for my car later as well.

I do not mean to threadjack but could a leaking manifold cause a burnt valve?

 

A vacuum gauge might work on a 4 cylinder tractor idling at 400 RPM, otherwise it's pretty hard to see a problem in an individual cylinder, especially with a large plenum.

 

I agree. We didn't use it often, and you are correct, only once or twice on a car/truck engine. I forget the spec, but you would look for the drop whenever the burnt valve operated. If you had a hot cam, you'd never find it with the vac gauge. Just a different method that I learned on years ago.

 

This appears to be a serious lack of skills/experience.

The dip & flutter of a vacuum gauge attached to the intake of an engine with a bad intake valve is distinct & obvious.

Elvis has left

 

That is what I have heard as a cause, a leaking exhaust manifold. I've seen burnt valves, but not on SBC motors. Usually the Dodge V6's, and some older foreign (Japanese) stuff.

 

Distinct and obvious when everything is agreeable, like the grind of the cam, engine speed, plenum volume, responsiveness of the gauge, length of the tubing, exactly how badly the valve leaks...

 

IMO--
Not a jack!! That Q does fit, & not a bad 1 at that!!

(edit)
Along the lines of Moe87--
How do you know when? What symptom(s) are looked at?

Way down on power all of a sudden? Knocking or ticking? {I mean not like a valve tick or header // manifold gasket leak tick} Smoke erraticly, such as when said cylinder(s) are on the exhaust stroke?

 

Loss of power. Its usually a gradual thing, I dont think you'd notice any noise out of the ordinary from the valve itself. Best way to check is compression test, IMO.

 

Thanks to all for the input and patience!!...

I understand now what it means, & what to do!