SOHC 4.0 Cracked Cylinder Wall?

[bpopp]

I had a leaky radiator that I ignored for too long. It eventually led to overheating while my son was driving and then I eventually noticed white smoke in my exhaust. This got worse and eventually I started having misfires. When I pulled the engines/heads, I found coolant in cylinder 1:

I like working on cars, but as you'll see, I'm still a novice. I originally assumed head gasket failure and/or warped heads and I was hoping to not rebuild the block (around 180k miles). It appeared to me that the gasket failed between the cylinders, but I honestly didn't see any obvious damage to the head gasket.

The heads are at the engine shop being cleaned, surfaced, and reworked. While I waited, I started cleaning up the block. There's some pitting around the water jackets, but it's flat and I don't believe the block surface is too bad. Unfortunately in cylinder 1 there was some staining and I started to worry that it was a crack and in a moment of weakness and panic, I scrubbed it gently with scotchbrite. It cleaned up, but I noticed that when I turn the crank, there's a straight bead of oil left on the cylinder wall. It feels perfectly smooth and I can't feel anything with a fingernail. Could this be a crack? As you can see, I unfortunately scratched up the wall of the cylinder with the scotchbrite.

Based on this cylinder, does this block need to be rebuilt? I'm not looking for this rebuild to last forever, but I dumped $500 into an OEM timing kit and another $500 for the heads and gaskets so I obviously don't want to throw a rod after a week. I'd be very happy to get another 50k miles out of it. Thanks for any advice.

 

[Mbrooks420]

Certainly doesn’t look good. Can you feel it with a fingernail?

Looks like the scotchbrite really bit into the cylinder. I wouldn’t have expected that, at all.

 

[J_C]

^ Depends on the scotchbrite color... going by the pads with sponges on them, pink or blue won't scratch metal, new green will and even scratch glass, brown will scratch just about anything that isn't near diamond hardness.

If I were already committed to the heads expense, I'd throw them back on and see what's what... fingers crossed.

The potential crack, why would oil be coming through it? I'd suspect piston ring wear... but that doesn't mean you don't have a crack.

 

[bpopp]

Hmm.. these Scotch Brite were red (extra fine).. which is what FordTechMakuloco recommended for scrubbing the deck surface. I assumed it would be okay for the cylinder walls. Some of the stuff I'm reading says this is fine and many people use this technique as a poor man's deglaze as long as the scratches are horizontal. Some people say it should be punishable by death (or thrown rod) because the abrasive inevitably gets in the oil/water passages and will cause the bearings to fail.

As a novice, the amount of disparate information out there on procedure is very frustrating. Without cutting corners, you leave a lot of money on the table, but It's hard to know where you can safely cut corners. The scratches honestly look worse in that picture than they are because of the magnification. All three pictures are after the scotchbrite so it isn't noticeable without a camera.

As for the oil, I just thought it was odd that oil seemed to move irregularly along that piston wall. It's clearly lower in that spot and I just don't know why. I really don't think there's a crack there big enough for anything to come through. I can see behind that cylinder from inside the water jacket and there doesn't appear to be anything unusual from that side.

It just got my attention because it's the same cylinder that had coolant and I didn't see any obvious damage to the head gasket or heads. I wish I had seen some obvious reason for the coolant to be there.

I've decided to go ahead and just tear down the bottom half and see what's there. I've been avoiding it because it seemed scary and expensive, but after researching it, I think it will only add a couple hundred bucks (assuming there's nothing especially nasty).