Pounder

Just the intake has to be removed or depending on the year !!! I have had the experience of the LS engines hard to refill with coolant and my theory was because the air could be trapped in the rear cyl. head. I did the all four corner mod three years ago and almost 20,000 miles. I had a PM to the above poster Bill Curlee on this issue and as you can see he has done this mod also. He is very wise so take it from there !!

aaronc7

I find it hard to believe that a little steam port is the root cause and you find plenty of people with the 4 corner steam vent that have similar #7 issues. To be honest, in my extensive searches I have come across many theories but very little good data/testing. At this point I'm just doing whatever I can do reduce heat-- be it coolant temps, combustion temps, short shifting on the track, etc.

Bill Curlee

Some people have attributed it to the two rear cylinders being hotter and running leaner than the others. Cylinder #7 worse than #8.

You have to ask your self; "WHY, or WHAT would cause that section of the piston to break???" It would have to BIND in that one spot because the cylinder or piston went out of round. Is the crack in the cylinder wall in the same area??

Could a combination of that cylinder being too lean and too hot cause that deformation??

If you flow tested all eight injectors and one injector had a little more flow than the others, I would put that one in #7

Just brain storming.



Bill

BURL

Old school suggestion. Those of you seriously into performance and concerned about #7. Put an EGT sensor you headers for #7 and one near front on opposite side of intake. Race with fuel normally used to race. Monitor gages in all aspects of engine condition - acceleration, deceleration, wide open throttle, idle to WOT, WOT to idle, etc. Is EGT (indicating lean) in any engine operating condition significantly higher on #7? If not look elsewhere other than mixture. Cooing, block problem, hot spots.

Would be interesting to start a thread and let every one who has experienced this problem send in their pics of the piston/cylinder. An similarities as to location and type of failure might become obvious.

Pounder

Common sense has served me well in my life. I look at the blocked off heads and think where can the water flow ????(very easy to trap air there) Plus it seems it is on the later LS 1 which are blocked off, not the early ones that at least have steam lines running from back to front.And it's the later LS 1's with the issue ??? WHY ??? The early ones still seem lower than the top of the cooling system, main reason I have all fours corners coming up and over connecting at the radiator. Whatever I am leaving mine as is !!!!

bmfvette

I understand your frustration.. It's not about the steam port...more about an air block within the coolant system.

You're correct that it's not the "only" cause of # 7 (or 8) dying.

As Bill suggests, could be a weak injector that ran the cylinder lean. Could be intake manifold design that ran the back cylinders lean (don't laugh this was discussed in length). Etc Etc Etc.

As 1st gen C5 owners that modified our cars, we took all precautions to eliminate the back two cylinders from puking on themselves. Cause lots threads on the forum were reporting failures. Most of us were not just daily driving the car.

Were just giving past experiences on what caused your ring land to find another home..

BURL

Again I'm old school but after studying the pictures the OP has shown I have my conclusion based on the following observations;

1. Piston thrust surface show no excessive scoring.
2. Piston combustion surface is good save a minor fuel wash pattern
3. Piston ring shows no scoring
4. Area above ring shows no scoring.
5. Appears there has been water in the cylinder.
6. There was some damage to cylinder head indicating the broken piston piece not melted - still hard.
7. Breakage pattern of the surface on piston indicates breakage from force - not from a hot spot or metal softening.

Conclusion - Fuel and air are compressible. Water is NOT COMPRESSIBLE. A large amount of water in a cylinder can bend rods break cranks, etc. The water WILL NOT BUDGE but something else will!

I believe a cylinder crack opened up on #7 under high engine temps and allowed a small amount of water into the combustion chamber and when the piston came up on compression - WHAM. This would be even more likely to happen if the water collected under the quench area where there is very little room (.040 - .060 - don't know exactly on LS engines) for water to puddle without cause damage.Then, with a chunk of piston missing, a large area or void near the leak was opened up to the piston and a channel was created to the top ring lands. The prevented further breakage by relieving pressure and the engine continued to run.

This may be a problem in some percentage LS1/LS6 blocks. Possible core shift (if that was still possible in the 2000"s) that leads to cylinder hot spots. Or just poor mold design or manufacturing tolerances when the blocks were cast , lined or bored. Maybe there were just a few defective molds so just a few bad blocks were produced. You would think if this is the case the engine builders would have recognized the tendency for this problem by now when doing sonic testing of blocks.

The rear coolant passage might help this situation by improving cooling and removing the tendency for #7 to crack or at least limit the extent of cracking. There may be people driving around now with a "weeping" #7 but because they don't push the cars the crack never open up enough to cause a problem - only symptom could be needing to add water a little more often than what would be considered normal

Just my .02 cents worth.

aaronc7

Thanks for the post and analysis BURL. I too and trying to sift through all of the observations and differentiate between the causes vs effects. I too feel like water getting in is what likely led to the rest of carnage. Still scratching my head over the root cause of the cracked liner/block though. There's data out there showing when guys ran the intake manifolds "backwards", 7/8 were still the problem cylinders, so I'm not totally buying the running lean thing... but then again I haven't done my own testing, so I try not to assume too many things. What's interesting is you see plenty of other #7 failures that look identical to mine. Same area of piston missing, basically same shape etc-- just google image search ls1 cracked piston or similar terms.

I have 400 miles on the new engine... break in pretty much complete. Signed up for a track day on 4-5 February, we'll see how it goes.

Pounder

one thing they I don't remember seeing is the fact of how hot these cars run. I didn't like seeing mine run up to 220 or more, been said that's in the design, well I don't know of any high performance engine that wants to run what I consider HOT !!! Heat kills a lot of engines, I have a 180 stat and the tuner has my fans coming on earlier. It runs at 192 all day and the highest I have seen it go in three summers is 206 !!! my two cents !!

BURL

Running lean did not cause this problem. Look at my observations. If it was a weak injector the resulting lean condition would have caused totally different damage - UNLESS it was severe detonation event and not prolonged heat.

Was your piston damage under the head quench area?

Thanks

aaronc7

Yes I agree, was just mentioning that because a few other guys brought it up. Injectors were flow tested after the fact and they were fine-- flow matched set.

As for the quench thing, I would say yes. I cropped a few pics to show the piston damage vs cc chamber/head. The cracked, but not broken off bit at the bottom lines up too.

BURL

OK, starting to get enough info for Root Cause Analysis. If you interested enough why not post for other #7 failure pictures on 2 or 3 areas of the Forum (Tech and FI. and General)

1. If the failures tend to be under the quench area then a small amount of water could cause more damage than in other areas of piston.

2. Opens up very small possibility of head piston contact in #7. You say I don't see any marks - well the marks went out the exhaust with the chunk of piston. This is kinda far fetched. What but what rods were you using? Engine twist? What did your quench area measure when you did build?? Read up on David Visard - see much the small block Chevy twisted from end to end at 6K RPM - you'll be surprised. That's the reason .030 - .035 quench was considered absolute minimum unless you wanted chance piston/head collusion. If you still have the heads examine the area of the quench pad very carefully - any marks?

BURL

1. How is the combustion chamber in the pick orientated to the cylinder pic? Is the piston break under the exhaust side of the quench area or the intake side?

2. Would you mind sending me a pic of the entire head so I can see combustion chambers on all cylinders yet have pic still be a relative close up?

Sorry to be so wordy. Won't bother you for a while after I get these answers. Thanks in advance.

aaronc7

No worries on the questions, I appreciating hearing your thoughts-- exactly why I posted this thread up.

0.) Reused the heads so I can't reference it now other than the pics below, but saw no evidence of piston hitting anything. Only damaage was some specks/nicks similar to top of the piston.

1.) The pic above if you were to take it and fold it in half like closing a book or something, that would be the alignment-- so the cracked side is under the intake valve.

2.) Only have 1 good pic that the shop sent me of the head. Going to post the direct links below so they will open up at full resolution:

https://i.imgur.com/SUJPyjn.jpg
https://i.imgur.com/1xQrvn9.jpg

BURL

Is that the ring gap directly under the broken portion of the piston?

aaronc7

Correct

BURL

Another large clue. Broken piece under quench area and ring gap under broken piece. But mostly on #7, not random - hot spot, cylinder crack, cylinder/block flex strongly suspected. Thinking on this. Will reply.

BURL

Still looking at this but in the mean time you and other guys tracking your cars may want to consider using "Water Wetter" or some other brand. May help with the hot spots if they exist. I know you went forged but hey, can't hurt. Stuff works pretty well.

aaronc7

I used water wetter once on my old turbo miata and it reacted with the coolant-- formed some brown gunk/solids, so I've been scared to run it ever since.

I haven't read any horror stories on here, I'm guessing its good to go w/ Dexcool.

bigmackloud

For what it's worth, I was running water wetter in my c5 when I had the cylinder 7 failure in Nov. I haven't touched my car yet, so I can't say what let loose but I suspect it will look like the OP's pictures. Every cylinder 7 failure I've seen pictures of failed in the each same spot. Many report cracking the block, but not all.

I also ran water wetter in my previous turbo miata (1992 1.6L) Which had 164k miles on it, motor had never been opened up, aftermarket turbo on it for close to 10 years, crappy piggyback tuning system... I was the 3rd owner to use as a dedicated track car. Sold to a guy who lives near road Atlanta and I hear it's still running strong. On a hp/L ratio, it put out way more than the corvette... yet never had a failure. Too bad my chevy wasn't built that well. I knew it was a mistake to sell that car, but I just had to go faster. Silly me.