af908

So, i thought all my Jeep needed was a head gasket. Changed it, started it up and it ran like complete crap. Had to floor the gas pedal to start it, and even when it did start it wouldnt idle unless i let it warm up a little. Even then it idled HORRIBLE, truck was shaking, etc.

I dont know what the hell i did, it ran fine before i pulled the head. Well, minus the coolant spewing through the exhaust, at least thats fixed now.

I noticed when i had the head off 2 or 3 cylinders had slight aluminum build up near the top. Im guessing when it overheated (which was the cause of the headgasket fail), the rings may have lost their tension, and some of the piston may have melted to the cylinder walls. Did a compression test, went something like this 110-25-26-100-50-x (didnt do the last cylinder, got frustrated and pulled the entire engine out after this). Also noticed that the dipstick was puffing out exhaust/air when i took it out.

So, OK, the lack of compression is whats causing it to run horrible... but WHY on earth did it run smooth when the head gasket was bad???

any ideas? anyone?

TheJerm

I dont know where the aluminum would come from, everything in the 4.0L is steel. I guess its time for you to stroke and bore that motor

http://www.jeepstrokers.com/forum/

af908

Even the pistons?

01 Laredo

TheJerm

all 4.0L are the same (TJ to XJ to WJ and ZJ's) and steel throughout The only aluminum on these motors are the intake manifold and accessory brackets

sgtskid

Not to mention the melting point of aluminum is 1220F.

af908

Maybe it wasnt aluminum, it sanded off a light blue color, sure as hell thought it was.

Maybe i wont have to buy new pistons. Hopfully just the rings then.

TheJerm

Thats not very high at all, Steel melts around 2000-3000F depending on its composition.

I'm willing to bet that you overheated the motor and melted the piston rings but where lucky enough not to seize the motor

sgtskid

You are correct, and the gases being combusted are normally around there. However, the parts should never get anywhere near that hot.

x2 on the rings, although that may have scratched cylinder walls.

af908

Thanks, ill let you guys know what i find tonight when i pull the pistons out of the block

af908

Umm, these pistons are definitely aluminum.

When i pulled it apart, i found the pistons had actually melted themselves to the rings, parts of the pistons were broken off, and that would explain the aluminum build up on the cylinder walls. Part of one of the pistons actually broke off when it came out of the engine.

Hopefully i will be able to just get away with cleaning the aluminum off the clyinder walls, theres no scoring so hopefully i wont need a bore.

3 pistons were like this.

freegdr

you need to hone out the cyl walls

af908

Yup sorry thats what i meant: hopefully i can get away with a hone and not pay for a bore.

freegdr

the tool looks like this use a lot of oil when using this

freegdr

as long a the cly are not scaRED YOU SHOULD BE OK

mwdouglas

can you post pics of the pistons