How many 4.0's before I find a good one...
 

Long story short: Bought a 2000 XJ for my brother in law, 180k miles on it with a thermostat bolt broken off in the head that someone tried (and failed) to weld something on to back it out. Bought it for $700 and the guy included another 4.0 that supposedly had "90k on it" from a 99 XJ.

Left the 2000 engine in the truck while I tore down the other engine. Eventually got down to the block and found out the #2 cylinder has some kind of ridge or crack in the middle of the bore. You can easily feel it with your finger. Not talking about the normal ridge at the top of the bore, it's a few inches down and goes all the way around in a jagged line. So that block is trash.

Just pulled the 2000 engine out of the XJ and go it on a stand. Took the head off last night to peak at the cylinder walls. YET AGAIN the #2 cylinder looks like it had problems. At the top of bore where the little buildup ridge normally is there's some raised hard parts that I can't account for. Pics below. I noticed the edge of the piston looks a little jacked up too... marks on the cylinder walls could be from that? I'll have tear down further to figure it out... but wtf!

I'm sure this comes down to previous owner neglect, but damn! Might be looking for yet another 4.0 block very soon.


https://cimg4.ibsrv.net/gimg/www.che...633a075c27.jpg

https://cimg5.ibsrv.net/gimg/www.che...0eecf51715.jpg

One of the raised sections, going to try and scrape it off without damaging the walls

https://cimg6.ibsrv.net/gimg/www.che...17567b32dc.jpg

Red square is the deformed part, no idea how that happens... detonation?

Okay, the white stuff at the top AND the marks on the piston are melted aluminum from a scuffed piston. Those marks on the piston are from the piston passing over the seized aluminum at the top. You can remove it with a ridge reamer. I think that piston is toast, however.

On the other block, take some sandpaper or a hone and see if that ring IS a crack or just a ring mark from the piston sitting there for a long time.

Thanks Dave, that's kind of what I was thinking the buildup at the top was. I'm hoping that the piston destroyed itself but didn't take the cylinder walls with it, I guess I won't know until I get the aluminum off and feel/measure it. Ideally the ridge reamer would get rid of the aluminum and then a nice hone will clean it up.

On the other block I did actually hone the cylinder with a ball hone and it didn't even touch the line/crack. I'll have to get a picture of it later. Definitely something going on with that one.

So last night I cleaned up the 2000 block just to get a better look at it (the one with the aluminum buildup at the top). I just happened to run my finger around the inside of the bore to see if I felt any deep scratches.

No deep scratches, but you actually FEEL the cylinder being out of round. The other cylinder a nice and smooth and round. #2 feels like there's parts of the cylinder wall that aren't round any more. Which would explain why the piston seems to have grenaded. Guess I'm looking for another block!

why not take the block to a machine shop and see if they can do anything with it.. maybe it just needs a bore and hone.

there is a lot of meat on those blocks. it can probably be bored out and have some oversized pistons installed. certainly not as cheap as JY direct swap but you'll have the satisfaction of knowing you have a fully built block with no mess ups. (depending on how good you are with a wrench which based on your posts it seems like you can get around).and you can take the 0 down in the back and make it 4.1:laughing:

Only one if you buy a reman engine from a known rebuilder most of the time cheapest in the long run.

Looks like I'll be taking one of these blocks to the machine shop. Over the weekend I picked up another 4.0 from an 01 XJ, supposedly with 130k on it.

The #2 cylinder looks great on this one... but the #3 cylinder DOES NOT. It looks like the head cracked and was leaking coolant into the #3 cylinder, piston is clean as a whistle. Coolant sitting in the cylinder for a while, however, caused some pitting on the wall. I've tried rubbing it off and using various chemicals to remove... Simple Green, WD-40, naval jelly... nothing touched it. I'll try a quick hone but I doubt it's coming off without boring.