Cracked or Blown?

OK you tech gurus out there Iv'e got a question. Is the 2.5 prone to cracking in the head or block, or is my problem with a blown head gasket. The 86 MJ known as Little Ugly blew her engine, (nice holes in the #4 position of the block, wave to your friends on the other side.) I replaced with another 86 2.5. 2 days later, she gets HOT, rattles. Shut her down fast, and had her (they are ALL feminine) towed home. My question is this, are cracked heads and/or blocks common with the 2.5. Any tips on increasing the survival of a head gasket, if thats the problem? I know that center punching the area between the cylinders works on the SB chevy, anything like that for the Heep 2.5
Thanks

The 2.5l are prone to cracking around the valve seats, not so much in the blocks. I would suspect a head gasket from what you described. I haven't had any particular problems with head gaskets though. Just deck the heads good when you take them off and check your block too. Wouldn't recommend center punching the block. The 2.5l is generally a very dependable engine and if you chose to do a complete rebuild will last a long time.

Alot of times when you only do one piston it will cause unequal pressure on the head gasket causing it to blow. Plus it can spin an older rod bearing pretty quick too.

Haven't pulled anything yet. I have always recommended others NOT to do single cylinder rebuilds, do all four or whatever at one time. I didn't know how close the water jacket is to the valve seats, so I wouldn't have thought to look there. She gets pulled in the garage this weekend, so I'm going to take a look then. Will planing the head raise compression much? I do want to get a little more power out of her, but I want to keep it sane.

tsgtbob said:

Haven't pulled anything yet. I have always recommended others NOT to do single cylinder rebuilds, do all four or whatever at one time. I didn't know how close the water jacket is to the valve seats, so I wouldn't have thought to look there. She gets pulled in the garage this weekend, so I'm going to take a look then. Will planing the head raise compression much? I do want to get a little more power out of her, but I want to keep it sane.

Click to expand...

Basically the 2.5 is the same as the 4.0 or 4.2 sans two cylinders. It's a gusty engine, we have two our TJ's, one was rolled completely over and ran upside down for a few seconds but otherwise runs fine now [smoked like hell for the first few mintes after we fired it off though]. If you are going to have it out and apart take a closer look, if the bores look good and the lip is good might want to hone the cyls a bit, new rings and new bearings. Both of ours have over 120,000mi and are rock solid but the 4:10's also make a big difference and make it bearable with 30x9.50's...

I am planning to just pull the head off of it. If things look iffy, then I will pull entire engine (again). She's got over 280 on the clock, this is the second engine in the bay. Right now she's got 3:55s and 31x10.50s on her, so she's a bit sluggish. I have a set of 4:10s from under a diesel XJ for her (anyone want a diesel XJ,, make me an offer) She's a good 'un, kinda unique for this area. I got her off of a buddy of mine, who got her off of Eagle. The MJ torch is burning brightly here in the Laurel Highlands of PA.