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so i have a 1981 280zx non turbo and the valve on cylinder 5 exhaust side, is stuck down. i taped it with a hammer poured marvels on it and it still wont return. thought it was lifters but recently found out n/a l28s did not have them. any insight on what to do helps.
 

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1983 280ZX Turbo
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Where I think this will end up is to pull the head and fix it correctly. Not sure if the cause would be a bent valve, but that's possible.

But to start with, you could buy one of the inexpensive fiber optic scopes that attach to a smart phone, pull the spark plug and look inside the cylinder. You might see something informative.

The idea of spraying the valve with penetrating oil (mentioned below) might be worthwhile, and if you get it working you would then change the oil and filter to get rid of the penetrating oil. Be patient, it may take a few days of soaking the valve stem to see if it will free up.

I would not suggest using a hammer on it. I also would not use pliers or vise grips of any kind to try and rotate the valve stem, because if you scratch or damage the valve stem the valve becomes useless. It will tear up your valve seal and you'll have to pull the head and replace the valve.
 

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Has the car been sitting for any length of time with ethanol fuel in it? I've had this issue on more than one occasion from bad fuel. Old/varnised fuel will cause valves to stick BAD. Most recently I had it happen to a '67 Dodge truck that has been in the family since new. Sat for a few months and went to crank it.. Cranked hard a couple of revolutions and wouldn't start. Pulled the valve cover to find every intake valve stuck, and as a result every push rod bent..

I haven't been under the valve cover of a Z for a number of years.. Is there enough room on the valve stem to get a pair of pliers or vise grips? Rotating the valve back and forth while pouring something (or letting it soak) in something thin like SeaFoam or maybe penetrating oil might help free it up. That's what I've done in the past. Hitting a valve with a hammer that's already bottomed out probably won't do much.
 
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