2.5 liter 4 cylinder pistons

[jaekl]

I have a question to the guys running 4 cylinders. I picked up a 88 Comanche with 104000 miles. Piston #2 and #4 had holes in them. The cylinder wall weren't too bad, so I put two new pistons in and at 115000 it is still running great. I've seen some others with this problem. Is it common?

Anybody have an idea what causes it? What does it sound or feel like when it happens? Under what conditions, high rpm or high torque?

My 86 XJ has 180000 miles on it with no problems. I was killing time at the dealer in the early nineties and the salesman was shocked that I hadn't had to rebuilt it yet. Great sales pitch.

[ryno1121]

It may be the timing. Not hard to check or have someone check for you.

[mjeff87]

I've got 174K on mine and still going strong. I did just replace the timing chain last weekend (see thread in the Projects section if you're interested) because the chain tensioner was worn out. Ignition timing is non-adjustable, so I don't think that would be the cause, but I suppose if the timing chain was too worn out the valve timing could be affected (late). I can say I really feel the difference with the new chain on the butt dyno :D

 

Maybe a bad case of preignition :dunno:

 

Jeff

[87manche]

I second the preignition theory. I had an 88 mazda 323 with the 1.6L motor and it had burned a hole through the piston on #3. It has always ran great, after I replaced the piston and put a timing light on it we discovered that the timing was advanced about 20*. I guess that explains why it was so peppy, but the ignition had literally melted the aluminum piston, there was metal splatter on the con-rod.

[jaekl]

The holes were near the spark plug.

I understand the preignition issue, but would it not affect all of the pistons? Also normal ignition is advance already so with extra advance piston farther down the bore.

Could it be happening on the exhaust stroke with a superheated plug?

I'll have to borrow a strobe light to check the timing.

[feerocknok]

The holes were near the spark plug.

I understand the preignition issue, but would it not affect all of the pistons? Also normal ignition is advance already so with extra advance piston farther down the bore.

Could it be happening on the exhaust stroke with a superheated plug?

I'll have to borrow a strobe light to check the timing.

 

Woohoo! This is what my old motor had done on piston #2!

 

I personally think the cause was this:

[Eagle]

I personally think the cause was this:

Ding!

 

I saw the first picture and thought the piston looked like it had sucked in some kind of projectile, then I got to the bottom, saw the bent valve, and said "Yep ... that'll do 'er."

 

The question is, why/how did it suck a valve? Must have had a keeper break.

[feerocknok]

I bought a new block and head not knowing what happened to the old one, but always wondering in order to prevent it from happening again.

Thought from reading this post that maybe it was a more common thing? :dunno:

[87manche]

The holes were near the spark plug.

I understand the preignition issue, but would it not affect all of the pistons? Also normal ignition is advance already so with extra advance piston farther down the bore.

Could it be happening on the exhaust stroke with a superheated plug?

I'll have to borrow a strobe light to check the timing.

some cylinders run hotter than others.

Ever have a VW bug? Lots of people ran a colder plug on cyl #3 cause it always ran hotter than the other 3.