bowtieman81

iTrader: (35)

Have you looked between the head gasket and block for any problems? Did not see a pic of the block surface.

LS1-450

iTrader: (33)

Yes, either the ring land or the piston. When I lost #5 & #7 pistons, no damage was done to the cylinder walls & I had a piece from #5 floating around in the combustion chamber for a bit prior to getting blown into the cat. It was in the chamber long enough to dent a valve & squash the end of the spark plug. Ring lands were damaged from heat & didn't scratch the walls either.

nytoy

iTrader: (3)

Yes, did it today, just didn't post pics yet. No signs of a coolant trail or anything amiss.

nytoy

iTrader: (3)

I was afraid of that. I just don't understand how that happens when I didnt overheat the car or run nitrous, and kept religous watch over the oil level.

rocketman442

iTrader: (8)

Where was the air going when you did the leakdown? Sounds like it was probably going to the crankcase huh?

nytoy

iTrader: (3)

Couldn't really tell, put my ear to the oil fill cap, to the exhaust and to the throttlebody and I still couldn't feel a thing.

Mike@TEA

Are you sure both valves were closed when you did the leakdown? Usually 100% will be a really obvious failure like a big hole in a piston or a broken valve etc. Could you hear the air leaking when you leaked it?

rocketman442

iTrader: (8)

Thats kinda weird, with that much leakage it should have been obvious, what kind of air pressure was you putting into the cylinder?

nytoy

iTrader: (3)

yep, I loosened the rockers so they were totally closed. That's what I figured as well, in retrospect, I should have drained the oil and put my ear to the oil drain on the pan. A little late now that the head is off.

nytoy

iTrader: (3)

100psi, standard leakdown testor. Compresion tests showed 30-60psi on #5 and 90psi on #7. all others normal.

I should add this engine was rebuilt 3000 miles ago if it matters, I want to blame the local engine builder, but I guess it could be anything.

warpwr

Usually the repair order/receipt has the warranty conditions on the reverse side. Like a GM dealer is usually 12 months or 12,000 miles. The local shop I use is 90 days or 4,000 miles.

Maybe your repair order has your warranty as well.

nytoy

iTrader: (3)

The engine builder is coming over tomorrow to look at it, although I doubt he can discover much more since the engine is still in the car. '

Thanks for all the help guys! Still open to suggestions! (wishing it wasn't the rings)

owen v8litew8

its looking more and more like busted / cracked ring lands on the pistons.

the ringlands cant support the rings and then you get no ring seal.
the rings might be in tact but with the lands on the piston being cracked, the rings arent doing anything, so you got no compression.

tims B16 cylinder walls were perfect even though he had compression losses like you, from ring land failure... just too much boost on his stock pistons. maybe the previous owner of your motor used nitrous, or at least some owner of the LS1 in question at some point during its life.

I can just hear the builder now.... "you said to reuse the pistons"
you'd respond "I wanted you to CHECK them to see if they were reusable"
and he'd say "I thought you just wanted new rings"
and on and on and on... this freakin sucks!

damn what a cool forum, lots of great ideas and responses! nice to see this kind of support!

linegtdt52

iTrader: (12)

Dude, is you cant see your ring is fried then you dont need to be under the hood of that car. you can see the space where the oil is comming through not to mention the oil sitting on top of the piston
stop accessing the heads

nytoy

iTrader: (3)

Easy there big fella, what you see sitting on top of the piston is coolant from when I pulled the head. Obviously it's been burning oil which you can see. I'm done "assessing" the head thank you.

LS1-450

iTrader: (33)

ntoy,

Please let us know how things go w/ the engine builder.

fast98

iTrader: (16)

pour some very light weight oil into all the cylinders, measure the amount of liquid and time how long it stays there. u could use wd40. you could even use trans fluid. a bad cylinder will leak right away..........

nytoy

iTrader: (3)

Ok here's the run down.

Sure enough, if you look just right you can see there is a huge chunk about 1" big missing from the end gaps of the ring on the #5. Engine builder pointed that out. Not much damage to the walls which is werid, still wondered where the chunk of ring went.

When he rebuilt the engine he didn't use a torq plate to hone it since it was a light hone.

So what I assume happened is, because the block is aluminum, once I put the head on and headbolts is distorted the cylinders so that they were out of round and this caused my oil burning problem from day one.

He now says, overbore the block, get over size pistons and he thinks a torq plate from a ford 351 can be used because it uses the same 10 bolt head bolt style. He will assemble it but I'm paying for pistons/rings/machine work.

I need to do some searching and may post a new thread, but here are my questions:

1. How far can you overbore a stock ls1 block? .20?
   
2. What over sized pistons can I use without rebalancing the rotating assembly? Builder says use cast, because stock has cast, using forged would throw off the balance because they are heavier. I don't run nitrous, just road race
   
3. For the torq plate and honing, is there special plate I should get so the machine shop doesn't screw it up, do you fully tighten down the head bolts? Is there a procedure right up for this somewhere?
   
4. what are the best rings to use for n/a?

Thanks for all the help!

owen v8litew8

ok, rock on! this is good news.

I would use OEM pistons and rings if they come in oversize.

you probably mean .020" for an overbore size... (thats .50mm) its easy to misplace the decimal.
.020" is commonly referred to as 20 thousandths.

Nemesis9

iTrader: (3)

If you are going to spend the money for new pistons, I personally would go forged and have the assembly rebalanced. If you change your mind down the road about FI, NO2, etc you be ok for whatever route you head down. Forged pistons are in the $600, not too expensive.