Burned Valve in a Miata???

[Bama GN]

I ran a compression test on my 1990 Miata and got 175, 165, 50, 165. Well, looks as though #3 cylinder has problems, huh? I suspect a burned valve. Anybody else have a guess? It has a consistent miss and idles rough.

Anybody have info on a website that might provide me information on how to pull the head and more importantly how to put it back!!

Paul.

 

[UNGN]

Pull the Head? Pull the motor and drop in a 5.0.

 

[John Larkin]

Might not be a burnt valve, might be bottom end. However if you hold a dollar bill in front of the tailpipe while running and it tries to suck it in, you'd feel better about it being a burnt valve. I was shocked the first time I saw the test but now I'm a believer.

As for instructions, these cars have been out since 1990 so Chilton's are available I'm sure. Best thing you can buy. Saved me a bunch of money on my wife's old Nissan.

 

[TurboMike]

Pour some motor oil into the suspect cylinder. Do the compression test again. If the compression comes up, it's the rights. If it don't, valve or headgasket. I've worked on a few Miatas..not tooo big of a job.

 

[Bama GN]

UNGN, that is a simple drop in replacement, right?

John, I did take a piece of paper and held over the tailpipe, but It wasn't conclusive. I will try the dollar bill trick. The exhause SOUNDS like a burned valve.

TurboMike, ya know, it might be a head gasket. I can hear a spitting noise. Guess I won't know until I get in there. I will buy the Chilton's manual.

Paul.