4.6is pistons after engine failure

[SamW]

My 4.6is blew its engine couple of years ago, most likely due to a timing chain guide failure and the engine can't be turned manually. So far the car has just been sitting in the yard but now I decided to look more into it.

I took pictures of the pistons of the passenger side cylinder bank through the spark plug hole and thought it would be interesting to share them.

As can be seen, all but one of them show significant marks on them, and being an interference engine, valve contact is likely. Although, to my eye the marks on top of the pistons definitely look interesting! Any ideas what could have happened?

EDIT: Just noticed the marks on the top two pictures look very similar, so I might have accidentally mixed the pictures but you get the point.

[X5chemist]

Interesting residue pictures. I've never seen any like those. Are they oil residue with bubbles spots?

[Factory6speed]

I'm not sure what the third picture is, but the other three that looks like carbon buildup that's caked on, that will flake right off if you touch it. That's what my m52 looked like. I flaked it off with a screwdriver. 30 years of 87 octane and poor maintenance.

[SamW]

I pictured the pistons in the driver's side also. Attached is a one of them, all looked quite similar. This definitely looks more like typical carbon buildup so I guess Factory6speed is correct. I believe it was the same thing in the passenger side but somehow it was much more severe. I might just have to open up the engine a bit more to see how it looks like in there.

[Factory6speed]

Here's one on the Google images, sorry about the size I don't know how to fix that on this website.



Not saying you don't have a valve mark there somewhere. But I think what is pictured is mostly heavy carbon buildup. When I had a piece of aluminum scrap in the combustion chamber of the b58, it didn't mark the pistons, but it made markings in the wet carbon build up that was on the pistons, and looked really scary through the camera. You can't really see anything in those cameras. At least I can't.

[X5chemist]

Poor fuel and maintenance? It's probably why mine smoked at start up and heavy foot acceleration. All gone now with good fuel and major maintenance issues fixed or up to date.

Tear it down!

[SamW]

As a matter of fact I have now started to tear it down a bit to see if I could pinpoint what went wrong with it.

I actually hadn't personally tried to rotate the engine by hand but it was done by the garage where it was initially towed to. So I first wanted to verify this myself and tried to rotate the engine from the crankshaft bolt after loosening all the spark plugs. Doesn't move at all in either direction. I would have thought that with a leverage arm of over 1 meter (+3 feet) there would still be some movement in some direction but it's completely stuck. The belts were still in place but I guess they shouldn't add that much of a resistance.

Also removed the passenger side valve cover but nothing extraordinary there, at least to my eyes.

I also dropped the lower oil pan being almost sure I would find pieces of chain guides there but it was all clear.

[Henn28]

Did the oil pump and chain look ok? Sounds like it may have been oil starved somehow and seized.

[Factory6speed]

Are you sure the car wasn't in gear (park)?

[SamW]

Originally Posted by Henn28

Did the oil pump and chain look ok? Sounds like it may have been oil starved somehow and seized.

Since I only removed the lower oil pan I was under impression that that oil pump and chain wouldn't be accessible. But now looking at the pictures online I wonder if the oil pump cover can be removed then exposing the pump itself and the chain without removing the upper pan?

Originally Posted by Factory6speed

Are you sure the car wasn't in gear (park)?

Also a fair point. I had to recheck this, and in fact it was in park! I put it to neutral and tried to turn the engine but it's still completely stuck.