I have zero compression is a cylinder doing a cold and dry test and a cold and wet test. Spark plug is black. All other cylinders were around 135-145 dry and cold. Is a valve stuck open? Maybe head gasket? Truck was smoking when running. Looks like new engine time
thank you for the help

 

valve stuck most likely or less likely hole in piston. hard to say with no compression at all. I have a bore cam. One can be had for about 30 bucks or less online. you could stick it into the cylinder for a quick inspection

 

Would that explain black spark plug? And bad valve seals? Wondering if it can’t be fixed and need new motor

 

wouldn't know until head is pulled. that is the definitive way to know.

 

Engine sounds fine when running just smoked a lot. Will pull head on it. Will looking under valve cover provide any clues?

 

A leak down test will tell you where the air is going. I'd do that next.

Air in exhaust would be exhaust valve, intake would be intake valve. If either of those, you might get away with just pulling the head and going through it. If you're less lucky, like me, the air will go into the crank case, revealing piston damage. No sense pulling the head then. Either pluck what you've got and rebuild or find a donor motor.

For what it's worth I ran my damaged 351w for 4 months with very little compression in one hole while I gathered parts and built the replacement engine for mine (truck is my only vehicle). One of the pistons melted and had a stuck ring. Thing ran somewhat OK to be honest, just smokey like you said. The failed motor in my case was already a reman, and flat tappet. So I found a low mile roller for a donor. In the end, the new motor is so much nicer to drive.

 

Thanks for the reply. I’m going to put a reman motor in it probably from rock auto. Are they decent?