355 misfire and stuck valve

Yes, walnut blasting is effective in removing carbon without causing damage to the alloys. It is just important to be sure to do it in a way that insures that all of the media is removed.

 

I would want to see if all of the valves are carboned up or just that cylinder. I don't think these cars are known for that issue unless there's something else going on, like worn valve guides, bad injector or something else letting oil into the combustion chamber or making the mixture go wonky.

Here's a decent video of the process. One of the reasons they use walnut shells is it won't do damage if it doesn't all get removed, unlike sand or similar, but the whole process occurs with vacuum suction going on to pull the media and debris out. This is a very common issue on earlier direct injection engines that didn't have secondary wet injectors to wash the valves.

 

You could try carbon cleaning if you are lucky. Usually, zero compression means the valve has burnt out due to carbon deposit keeping the face of the valve from contacting the head to dissipate the heat into the head.

 

You can do the actual blasting with the engine in the car. Access to the intake valves is from the top and that is easy enough to get to. Access to the exhaust valve is from the side or the bottom after you remove the headers and that is a job in itself.

It's been my experience that the exhaust valves have more problem. Did the shop confirm what valve is having problem? Perhaps just do that cylinder.

 

That carbon buildup is being caused by something. Step one is figuring out what is causing it.

 

No idea what's wrong, but based on the pic it's a lot of buildup, and it appears oily. I assume the pic is taken from inside the cylinder and we're looking up at the faces of the valves? Walnut shell blasting is for the back side of the valves, not inside the combustion chamber. I suspect you're going to be taking the heads off.

 

I think you need a valve job.