So why do I have no compression in #5 cylinder? pics with head off
#22
Originally Posted by nytoy
the #5 Exhaust port on the manifold has a lot of carbon, plus soaking wet with oil. So it's a ring issue, even though the walls are not scored?
Like the ringland could be cracked or something like that?
Like the ringland could be cracked or something like that?
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Originally Posted by bowtieman81
Have you looked between the head gasket and block for any problems? Did not see a pic of the block surface.
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Originally Posted by LS1-450
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.
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Originally Posted by rocketman442
Where was the air going when you did the leakdown? Sounds like it was probably going to the crankcase huh?
#27
Originally Posted by nytoy
I did, 100% loss in #5, as in nothing sealing anywhere!
80% loss in #7
I pulled the head gasket off and it looks fine, no tears anywhere, no coolant trails on the block or head, so I am doubting that the coolant went under or over the gasket.
I poured some gas in the exhaust and intake ports on the head and it's tight as a drum.
I'm still shocked it could be a ring issue but leave no marks or traces on the cylinder wall.
My rebuilder is coming over tomorrow afternoon to look at it, should I start getting on his case about assembling it wrong or not untill I pull the engine and pistons out and figure out what happened?
80% loss in #7
I pulled the head gasket off and it looks fine, no tears anywhere, no coolant trails on the block or head, so I am doubting that the coolant went under or over the gasket.
I poured some gas in the exhaust and intake ports on the head and it's tight as a drum.
I'm still shocked it could be a ring issue but leave no marks or traces on the cylinder wall.
My rebuilder is coming over tomorrow afternoon to look at it, should I start getting on his case about assembling it wrong or not untill I pull the engine and pistons out and figure out what happened?
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?
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Originally Posted by 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?
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Originally Posted by rocketman442
Thats kinda weird, with that much leakage it should have been obvious, what kind of air pressure was you putting into the cylinder?
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.
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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.
Maybe your repair order has your warranty as well.
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Originally Posted by 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.
Maybe your repair order has your warranty as well.
Thanks for all the help guys! Still open to suggestions! (wishing it wasn't the rings)
#33
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!
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!
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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
stop accessing the heads
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Originally Posted by linegtdt52
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
stop accessing the heads
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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..........
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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:
Thanks for all the help!
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:
- How far can you overbore a stock ls1 block? .20?
- 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
- 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?
- what are the best rings to use for n/a?
Thanks for all the help!
#39
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.
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.
#40
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.