youguessit

when my motor did that it didnt burn oil but fuel got into the oil... was wierd. till i pulled the heads off i mean. Did it in 7. sam **** only on the very top of piston. didnt hurt the heads. Detonated off....

RENE'S RAGE

iTrader: (96)

The piston probally broke off alittle at a time, as to one big chunk.
Shot out the exhaust, in small peices.

demonpixel

iTrader: (19)

Maybe so....still...I've heard stories of people dropping a small nut down an intake manifold and have it wreak havoc everywhere.

RENE'S RAGE

iTrader: (96)

Oh yeah, I was just saying maybe that's why you didn't find a large chunk of piston anywhere and no other damage.

66 BADBOY

iTrader: (2)

I don't wanna sound like a moron, but would this type of damage show up if a compression test was done on a motor? Just curious because I picked up a 60K mile 2001 LS1/A4 the other day. Compression checks were all around 185-195.

I'm wondering if its a good idea just to pull the heads to be sure? Or should I not worry about it because of the compression tests results?

demonpixel

iTrader: (19)

I don't think it would show up as much, because there's not an explosion going off. Combustion is not happening; the piston is just moving up and down.

Now, people will tell you that it's always a good idea to tear down a junkyard/used motor, and no one will tell you that you should pull a junkyard motor and run it in whatever car you want to put it in.

No one will ever tell you that, BUT people do it, and it turns out fine. Having said that, you don't know if anyone's run nitrous through a junkyard/used motor, or ran low octane gas when they should have run higher octane gas, etc.

It takes a little time (and money since you have to get new head bolts) to pull the heads on a used motor, but it's never a BAD idea to do so.

I'm glad I pulled the heads on mine man. A broken piston sucks, but it could have been way worse. I just put the oil rings and piston rings on the new piston and the machine shop already hung the piston on the rod, so I'm about to clean the deck surface and the head surface and put in the new piston.

I think the broken piston piece DID go out the intake, because there are some weird scratches around the cathedral port. Nothing that would cause sealing issues with the intake manifold; it just doesn't look normal.

KCS

iTrader: (20)

If it's a bunch of pieces, then the chances should be better that at least one of them would have been left behind, or at least leave evidence, like a marking or something. To have them all leave out of the exhaust valve all nice and neat just doesn't seem likely. Not to mention, it would have to travel across the cylinder to reach the exhaust valve, when the intake valve and quench pad are right above it.

KCS

iTrader: (20)

I don't know about a compression test, but possibly a leakdown test.

peedeerooster

iTrader: (1)

I have a 2005 CTSV. I had installed a Fast 92mm, NW 90mm ported TB, TFS 215cc heads, headers and all the usual boltons. The car was around 480 rwhp on the stock longblock. The AFR was in the 12.7 range and timing was 24 degress. After about 20,000 miles with the head, cam and intake, the engine started burning oil and smoking. Tore the engine down and you could move the #7 piston around in the bore with your thumbs. All other cylinders were tight and in good shape. I didn't have anything broken like the piston or rings. It just looked worn out. The shortblock was factory and only had 46,000 miles on it. Just put in a forged 408 shortblock. Will see what happens now.

Chalky

iTrader: (2)

Same thing happened to my old 02 Z. 11.5:1 CR, tuned. Broke off in same place.

Pulled the piston and wrist pin was almost frozen solid, piston woudl just barely rock on wrist pin.

demonpixel

iTrader: (19)

Well guys, I got a new piston and went to go install it today. Can't believe I didn't notice this before, but check this out, looks f'd up:





This is the #7 cylinder bore. I have no idea if that's fixable or not. Ran my finger over it and you can definitely feel a change in surface. Not comfortable putting that piston in now.

So now I'm trying to think of what options I have. So far I've come up with these options:

1. Tear everything down, take it to a machine shop, see if they can repair it and if so, pay the $$ and put everything back together.

2. Tear everything down, find a good stock block that's got good 8 cylinders, and swap everything over to it.

3. Start completely over with a new LS engine.

4. Give up and sell everything.

I feel like total **** right now because it feels like I'm basically one cylinder away from having a good daily driver muscle car.

Anyone else have any other options? Thanks guys, I appreciate the advice.

KCS

iTrader: (20)

That looks like a crack, but it might just be some crud on the cylinder wall. Take it to a machine shop and they can bump it in the hone very lightly and see whether it's cracked or not. You may get lucky...then again, nothing else has really gone right with this thing.

demonpixel

iTrader: (19)

Hmmm...would a flex hone help before taking it to the machine shop (I've never flex honed before)? One of these:



I heard flex honing doesn't change the bore diameter, so I should still be able to use the stock piston/rings, correct?

KCS

iTrader: (20)

Maybe not. In a rigid hone, like at a machine shop, if it's cracked it would leave a shadow where the stones didn't touch. A flex hone is designed to conform to whatever shape the bore is in, so you won't get that same effect. It'll just clean up the cylinder, but that's what the rigid hone is going to do anyways.

redz_02

iTrader: (4)

Can't you overbore the cylinders .05? Would that clean it up?

I thought a flex hone is just to polish/debur the cylinder walls.

demonpixel

iTrader: (19)

If I bore it 0.050 over, and get a new piston for it, I'm not sure how bad that would throw off the balancing of the rotating assembly.

KCS can probably confirm this.

KCS

iTrader: (20)

Not .05", but you can hone it .005". If the sleeve is cracked, it's typically all the way through and sometimes the aluminum behind it is cracked as well. It's repairable, just probably not worth it on an LS1 block.

Flex Hones can restore surface finishes on a cylinder wall for a new set of rings to seat. It's not going to change the bore geometry, or remove enough material to use a larger piston, but it can be used just to get a nice new surface finish for a rebuild.

Also, yeah a .005" over piston probably will throw off the balance a considerable amount. Not necessarily because it's a larger piston, but the material is different and can be heavier itself.

demonpixel

iTrader: (19)

Block is junk because of the crack.

The hunt is on for a new block...

sjsingle1

iTrader: (1)

so still no clues as to why this happens to so many engines????

demonpixel

iTrader: (19)

I was told that it's because of the intake manifold design. #7 is the last to get air, the air is denser, and this creates a lean condition. Increase the heat a little, or clog your #7 injector a little, and your #7 piston goes at the ringland.