dantj

Decided to tear the LQ4 down that was in my Jeep to freshen it up. Had some noise previously but i narrowed it down to lifters, and MMO freed them up. Motor had zero noise after this, just burned a bit of oil.

# 5 was replaced about 15k ago. Thats why the piston is a little cleaner.


Anyways, everything looked good, til i pulled the pistons out.

#2, #5, and #7 are all cracked in pretty much the same spot. Upper corner closest to the front of the motor.

No real signs of wear in the bore, bearings all looked great. Lifters were good, and cam bearings were slightly worn.

I'm running less timing than stock on 93oct. Couldn't add any timing due to knock retard popping up. Motor is bone stock.

mark21742

What compression ratio were you running? It sounds like you were getting a lot of detonation which killed the ring lands.

.boB

iTrader: (1)

Sure looks like detonation. What do the heads look like? And the tops of the pistons?

dantj

Stock compression 9.4:1

Heads and tops of the pistons don't look about normal for a high mileage engine. I haven't had a chance to closely inspect the heads yet.

A.R. Shale Targa

iTrader: (2)

My guess is it was majorly overheated in a front end collision.

RockinWs6

Very common problem with these stock GM pistons, fragile junk. They break if you look at them wrong.

dantj

Not sure if thats sarcasm or not, but funny that you say that...

Came out of an 01 denali that rolled 7 times. I've put 30k on it since.

However, about 15k ago, I cracked the upper ringland on #5. No damage other than the piston. Swapped it out, and changed out the injector too. So being that all 3 of these cracked in the same spot, I'm thinking that it happened in the last 15k miles.

Its also overheated once on me. Threw the belt after hitting a snow drift and I didn't notice it until it was too late.

A.R. Shale Targa

iTrader: (2)

I was totally serious. The overheating causes the ring ends to close and butt together. The aluminum breaks from the pinch.
When hot rod twin turbo'd that 4.8 to over 1200 HP with the JY short block, the only mod they did was to open the ring gaps.

Old Geezer

iTrader: (3)

"Came out of an 01 denali that rolled 7 times"
Had a lo mile Silverado that rolled. The dumass wrecker driver got it up on the wheels, and tried to start it. Kicked 2 rods out due to oil in the cyls. Yours could have suffered the same fate, sans the rod damage.

RockinWs6

Good Post.