Hello,
I have 1998 f150 4.6L I got from a friend, changed the fuel pump and it ran great. Then I changed the oil and it had a knock so I pulled the engine thinking I had a slipped bearing. Instead I found piston damage on 1 and 2. The thing that gets me is they are in the same spot on the pistons and the same shape. I'm trying to figure out what happened, maybe you guys can help. I'm going to go through with a rebuild.

Piston number 2.

Piston number 1

Head number 1

Head number 2

 

How many miles?

 

Did you clean the areas where the chips in the piston are? It looks like impact damage to me. The questions is what? Spark plug? Valve? Something got sucked in? In the top picture of the cylinder head it almost looks like some damage at the top of the pic to the intake valve. Another reason I say some kind of impact in the bottom pic of the piston it looks like another ding near the chip.

 

I dont know how many miles are on it. This is a replaced engine. I wiped off the cylinder heads but didnt really scrub into it. The spark plug looks like it sits to far inward for it to be spark plug damage. All the spark plugs looked good as well. The thing that doesn't make sense about this, if it was from something getting in engine, is that it's on 1 and 2.

 

I would just guess that what ever got in the engine got spit out or someone took it apart enough to fix it. Like if it dropped a valve they just fixed that but didn't fix the pistons. Broken timing belt/chain could have caused a couple of valves to collide with the pistons also. One reason on asked on cleaning it, it looks cleaner on the pistons where the chips are.

 

Right now that's only suspect for the knock I was having after I changed the oil. Everything else looked good. I couldn't find any evidence of bearing slippage or stuck valves. Would those two grooves be enough damage to cause an engine knock?

 

Too bad you've already pulled the engine. I think that there are some simple tests you could have done to determine if it was a bad bearing while it was running. Could be something else,like a loose torque converter bolt.

Beside that, why are you pulling pistons if you think that you spun (span?) a bearing? No offense, having initiative is generally a good thing, but I think that you've jumped way ahead and are kind of shooting in the dark. How do the bearings look?

Are those the heads that blow spark plugs? Doesn't seem to be any thread to hold them. Scary just to see from that side.

 

I started off just trying to check for things without pulling everything, couldn't find anything so I would dig deeper, couldn't find anything so I dug deeper. Wasnt until I actually pulled a piston that I found the groove. I don't think they are the heads the blow plugs. I know the 5.4 has the problem with the metal sheath breaking off into the piston.

 

Here's a thought related to the piston damage. Maybe the pistons got damaged when whatever made that mark got jammed in there. Check the piston skirt dimensions. Piston slap makes a knocking noise.

Any chance that somebody stuck something in to a plug hole and pounded on a piston? Can't tell the orientation from the pictures.

 

I keep looking at the top pic of the head. I see like a part of the valve or more likely the seat is missing. Might just be the light though. If its a used engine and not the original its hard to say what was done. The pistons could be from just about any engine. I'd say you need two new ones for sure.