Ryan3481

SO this 00 Cherokee 4.0L I picked up, in what I thought was excellent condition, starts to misfire and trigger the engine light. Its high miles, so I figure no problem - just a little carbon buildup. Take the head off and am having my buddy clean the valves. After further inspection, valve #3 and #6 need it so we doing the entire thing to clean it up.

Then we notice that piston #2 is slightly melted. We were wondering if it was from the misfire, but then put two and two together. A lot of the car's cooling system has been replaced / looks new. We think it had been run overheated at some point, the previous owner changed the cooling system parts and then sold it when he saw the piston (or didn't know about it, but the new head gasket tells me something). But currently the piston is not triggering any issue with the engine light, and is still working OK. How dangerous is it to continue to drive the car now that we know this piston is in the condition it is? That is now my concern. The compression seems to be OK since it is not triggering the computer..

What I will eventually do is replace with a used, lower mileage engine. Reading other threads, I can see that is the most cost effective way to solve this issue: https://www.cherokeeforum.com/f2/jee...-64211/index3/

But I don't have the money for the used engine + install now, and this is my everyday ride. I just want to get people's feedback on how safe I am to drive it for the time being. I do not drive this thing aggressively, do not red line it, use all synthetics and maintain it to a T. I am just concerned about how long it could last in this condition. I guess in the end, I have no choice but to find out and see what the F happens..

Let me know what you all think.

KD3NE

Was it running really rough?

Can you take a pic of the piston or is it back together?

Years ago I had a truck that began to run really rough.

Turn out I had burned a hole in the piston.

I wonder if you don't have a very tiny hole where it is melted?


If it is back together do a compression test on that cylinder.

JeepingDan

Got a picture so I can give a rough estimate?

Ryan3481

actually, it was not running really rough. There was a bit of shake to the engine at idle, and we think that was the misfiring on the two valves -so the valves is what brought us to take the cover off and is what we are fixing now. it wasnt until we had the cover off that we even saw the issue with piston #2.

i may be able to snap a pic tomorrow if he hasn't put the cover back on yet. i'll post on the thread here if i do get a pic. i'll also inspect to see how far down the damage looks like it went on the piston. I've read that if the damage is on the top and not all the way through it could be fine.

fishtaconc

Most likley the melted piston was caused by a lean condition in that cylinder, probally from a dirty clogged injector althogh if it was overheated it may have been pre ignition. Either way it may be wise to clean the injectors.

Ryan3481

def cleaning the injectors in case that was the issue, but can I continue to operate it with the damage to the piston?

how will I know if the piston damage starts to become an issue, other than having it lock up while I'm driving?

Ryan3481

so the piston is just really slightly warped. i'll get a photo up tomorrow.

i'm going to do a compression test done too. if they are all within 15lbs of one another, I should be OK, right?

A_Jeepr

Replace the piston, yes it is ok to drive, however.

The piston got hot, it lost some of its shape. larger at the bottom than the top, only by a few thousands of an inch. This allows the top to expand and seal even better once the engine is warm. When the top of the piston "melts" it changes shape 2 things could have happened.

The piston might be out of round now, and or the top of the piston is larger at the top than it should be. This will cause rapid wear in the cylinder walls and could mean an engine rebuild later down the road.

Why take the chance? i wouldn't. its not hard to drop the pan, mic the cylinder with a bore gauge and change the piston while the engines in the Jeep.

My 2 cents.

Ryan3481

Here are pics of Piston #2. After looking at it again with my buddy, we determined that this piston just got hot and melted a bit of the aluminum off the top of the piston and on to the top / side of the cylinder. If you are looking at the pic of the entire piston head on, there is a bit of aluminum at 12 o'clock and 6 o'clock. The cylinder wall below this is clean and fine, and the piston is fine and has clean movement. This slight damage was at the very top, and is not below the rings. We did a compression test and everything checked out OK.

My only question is, do I leave the aluminum at the top of the cylinder, or try to remove. I don't want to do any damage in removing it, so I am kind of inclined to leave it be. The piston comes up to the top of the cylinder and sits flush with the bit of aluminum on the wall - there does not look to be any contact or rubbing.

I look forward to your thoughts.

A_Jeepr

looks like carbon burns. it should be fine.

not enough damage was done it looks to cause a problem. the very top 1/8 inch of the piston collects carbon, nothing else. as long as it didn't reach the first grove, jeep on

JeepingDan

X2 as long as it has good compression then you will be fine.

Honestly I was expecting something much worse.

84zmyfavorite

Last weekend I pulled the head on my 99, and found a very similar story on cylinder/piston #2. It caused the wrist pin to oval out the piston. Id replace at least that piston. Complete piston and ring sets on eBay for under $200.