Valve Stuck ... Damaged Piston ... Options?
 

Ok, so I finally got around to tearing town the 2004 DII that had Zero compression in Cylinder 7, other than that all but the power steering pump seems to work fine.

I thought I would just be replacing the HGs. As soon as I pulled the head the problem was obvious. Valve stuck and broke and really marred up the piston and the head.

What are my options here? I have another Head from the 4.0 I pulled from our other 2000 DII.

What is involved in replacing the 1 piston? Can it be done without pulling the engine? What happens if I do nothing with the piston and fix from there up? power loss? catastrophic failure?



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If it were me I would clean up the top of that piston and look for any cracks. If it is just marred up I would run it. Fix your valve, do the HG and cross your fingers.

You're gonna wanna pull that piston and rod out and check it thoroughly. Something has to give, and if it was smacking like that, there is a possibility of a twisted or bent rod. If rod is okay, you can probably get away with smoothing out and cleaning up any ridges or marks on the piston

That head won't be worth the cost to machine out and repair the damage from the dropped valve seat. Best to get a used or already reconditioned head and call it a day

OK. I have 2 complete heads and valves from a 4.0 and from everything I have read they are the same as the 4.6. I will pull those heads off tonight and see how they look and pick the best 2 to have resurfaced. The valves and springs almost look new on the head with the damaged valve seat,
I was hoping to do this without pulling the front cover, oil pan, etc ....

I got this Disco for a great deal and knew it was going to be a project.

For as much as you have it tore down I would recommend replacing the entire engine. Even if you swap the heads and clean up the piston there could be damage to the connecting rod or even the cam. If the rod lets go you're back at square one.

IDK, I wouldn't pull the whole engine for that damage, I'd bet the conn rod is fine. Looks like you just lost the seat so it's not like you dropped the whole valve and had it banging around in the cylinder. Since it was running fine prior, I would clean up the face of the piston, replace the head (the 4.0s are the same), and button everything back up. That's assuming you are not building some bullet-proof overland truck.

measure the piston deck height, if the rod is bent the piston won't come up as high as the others.

I agree on pulling the piston and rod out for a good inspection, want to make sure the rod bearing is good. Just use the other head, not worth the cost to fix that one if you have another set ready to go.

When I was a kid about 40 years ago my little brother built a Camaro motor with high dome pistons. He put them in 180 degrees off. Hell of a noise when he tried to fire it.

If desired, you *can* pull that piston without pulling the entire motor out. Simply drain the oil, remove the oil pan, and with the heads off of the top, you'll have enough access to undo the piston from the bottom and pull out via the top.

I'm not telling you to do that. You can. It's fine to do it that way. I'm just pointing out that's an option.




I do think that you want to figure out *why* you had a piston collide with a valve, though.