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Photos are cylinder 2 only, cylinder 6 has only a valve seat issue with no damage to piston or head. I suspect the exhaust valve burned up for #2 and 6, but 2 got it bad.
I'm looking at two options:
Grind down the piston smooth, hone out they cylinder wall, pull the valves, get the seats reground, clean the valves and replace as needed. I'm expecting to replace the 2 exhaust valves. 500 total
or
Pull the engine, do a full stock rebuild replacing the piston with a used piston, all new bearings, seals, and rings. TSP ported heads. 2k total
I need advice on the best use of my time. If I can run the the engine for more than a year I'll be happy. It will take me 6 months to pull and rebuild vs 2 weeks to shadetree it.
Looks like the spark plug strap snapped and didn't go out the exhaust fast enough. I'm not sure it would do quite that much damage though. Maybe a ring let go and bounced around for a while. Really could have been a dozen things. Perfect time for cnc heads and a stroker kit.
Those almost look like eyebrows on the piston tops from valves coming in contact with the piston. Or is it just a wipe of the crud on top of the piston? Some of the build up looks like normal carbon fouling. I would clean up the pistons and cylinders as is to get a good look before disassembling the bottom end. You might be able to get away with repairing the heads and running it.
Looks like the spark plug strap snapped and didn't go out the exhaust fast enough.
Marks look about that size, It really looks like something just came through the intake and got stuck in the cylinder. I can accept that as an answer.
The real question I have now is: Can I use this piston?
I want to sand/grind the piston smooth, get the head done, and go. It's the difference between months of downtime and days of downtime. If it blows up in the future it blows up...
Marks look about that size, It really looks like something just came through the intake and got stuck in the cylinder. I can accept that as an answer.
The real question I have now is: Can I use this piston?
I want to sand/grind the piston smooth, get the head done, and go. It's the difference between months of downtime and days of downtime. If it blows up in the future it blows up...
I would smooth out the piston and get the head done, then pop it on and do a leak down test. You’ll know right away if the rings are trash before you waste time putting it all back together for nothing.
Marks look about that size, It really looks like something just came through the intake and got stuck in the cylinder. I can accept that as an answer.
The real question I have now is: Can I use this piston?
I want to sand/grind the piston smooth, get the head done, and go. It's the difference between months of downtime and days of downtime. If it blows up in the future it blows up...
The piston looks fine. Clean it up. I had a keeper let go about two years ago and dropped the valve. It hit the piston and left a bigger mark than on your piston. The piston hit the valve so hard that it bent the valve and broke the valve guide boss. The machine shop had to weld the boss to put in a new guide. The piston however, is fine and I have driven the car over 10 K miles since then.
While the cylinder walls on these motors are thin, the rods and pistons are strong. Do the valve job and restart the car. BTW. your estimate for the head work is too high. My machinist charges 90 per head for labor plus parts such as valves, seals, etc. The repair should cost about $300.00.
The piston looks fine. Clean it up. I had a keeper let go about two years ago and dropped the valve. It hit the piston and left a bigger mark than on your piston. The piston hit the valve so hard that it bent the valve and broke the valve guide boss. The machine shop had to weld the boss to put in a new guide. The piston however, is fine and I have driven the car over 10 K miles since then.
While the cylinder walls on these motors are thin, the rods and pistons are strong. Do the valve job and restart the car. BTW. your estimate for the head work is too high. My machinist charges 90 per head for labor plus parts such as valves, seals, etc. The repair should cost about $300.00.
Thanks for the insights. Especially the advice on head job pricing...
I've cleaned up the piston, it does not look so hot. There are some deep cavities you can see. Will be honing this cylinder and should take care of the scratching. I'm gunna give it a go.
Machine shop is closed today for the holiday. I'll be dropping the heads off monday, hopefully he can get it back by next weekend!
OK. And the piston doesn't look bad. The piston crowns in these motors are real thick. I also believe something entered the cylinder. You should know by now if the ground strap came off the spark plug. If not, then something entered through the intact tract like a stone or a washer, etc. Good luck to you, and post the results.
So I cleaned all 8 pistons today, and honed the #2 cylinder wall with moderate damage. Cleaned up mostly.
I noticed on #7 there is also similar looking damage, but not quite as severe. Something must have got in the intake...
But what’s the odds? Had to get through air filter and MAF. I’d have to carefully inspect those rings on both cylinders. GM started using low tension rings in 02’ I believe, maybe a ring end broke off? I’m guessing for sure, but I doubt very seriously it came in through intake. I’d say it’s internal.
But what’s the odds? Had to get through air filter and MAF. I’d have to carefully inspect those rings on both cylinders. GM started using low tension rings in 02’ I believe, maybe a ring end broke off? I’m guessing for sure, but I doubt very seriously it came in through intake. I’d say it’s internal.
Nah. If a ring or land broke it would show scoring on the cylinder walls. This something that entered through the intake tract. Example: A few years ago I took the CAI off my car to do other work. I noticed a pebble on the MAF screen. It was about the size of a BB. I never ran the car without the CAI, and do not know how the pebble entered the intake tract. I have noticed this phenomena over the years with carburated motors as well as injected. Somehow, substantial sized pieces can and do enter the intake tract. Go figure.
Nah. If a ring or land broke it would show scoring on the cylinder walls. This something that entered through the intake tract. Example: A few years ago I took the CAI off my car to do other work. I noticed a pebble on the MAF screen. It was about the size of a BB. I never ran the car without the CAI, and do not know how the pebble entered the intake tract. I have noticed this phenomena over the years with carburated motors as well as injected. Somehow, substantial sized pieces can and do enter the intake tract. Go figure.
If you look closely you can see some scratches in the cylinder wall, but I wouldn't describe it as scoring really. I have them mostly honed out. I imagine somebody was working with the intake manifold off and got exposed to a washer or something. It's also very possible these are two separate events, valve seat/bend issue and the piston damage.
I got the heads to the machine shop and the machinist reports two bent valves. Getting valve job, exhaust valves replaced with SS Manley valves, and all new OEM springs. I'm not too keen on the cost but it is competitive.; Cleaning, valve job, new seals, new exhaust valves for 550 both heads. To compare, TSP has PRC Stage 2 with all new valves 950 plus tax. I'm all stock so I stuck with just a repair.
I get the heads back friday, saturday I will check compression and leakdown to check for ring damage.
Heads installed and the car runs. I just installed and fired up, no compression test. It runs fine now!
I'm having other accessory issues like leaky water pump, no power steering, and no brakes i have to pump up to build pressure. Getting those sorted this week I hope.
LS intakes are notorious for collecting trash if they were ever on a blown up motor. Was the intake on a blowed up motor at some point?
If not did you drop some spark plug straps?
I had a valve break a considerable size chunk off once and did no damage at all, then another time I sprayed the absolute **** out of that motor one night and dropped a spark plug strap and left a huge scratch in the cylinder wall. Go figure a chunk of valve does nothing and a spark plug strap takes out a cylinder.
LS intakes are notorious for collecting trash if they were ever on a blown up motor. Was the intake on a blowed up motor at some point?
If not did you drop some spark plug straps?
I had a valve break a considerable size chunk off once and did no damage at all, then another time I sprayed the absolute **** out of that motor one night and dropped a spark plug strap and left a huge scratch in the cylinder wall. Go figure a chunk of valve does nothing and a spark plug strap takes out a cylinder.
I can kinda see it. A plug strap is small enough to get into all kinds of trouble, like between piston and cylinder if it tries hard enough (lol), but a big chunk of valve will just bounce around and HOPEFULLY get blown out the exhaust. Or get caught, bend a valve or hang one open, or just get pounded into the piston. If you're lucky....
If you look closely you can see some scratches in the cylinder wall, but I wouldn't describe it as scoring really. I have them mostly honed out. I imagine somebody was working with the intake manifold off and got exposed to a washer or something. It's also very possible these are two separate events, valve seat/bend issue and the piston damage.
I got the heads to the machine shop and the machinist reports two bent valves. Getting valve job, exhaust valves replaced with SS Manley valves, and all new OEM springs. I'm not too keen on the cost but it is competitive.; Cleaning, valve job, new seals, new exhaust valves for 550 both heads. To compare, TSP has PRC Stage 2 with all new valves 950 plus tax. I'm all stock so I stuck with just a repair.
I get the heads back friday, saturday I will check compression and leakdown to check for ring damage.
Yea, thats a little high. When I lost a keeper and dropped a valve as mentioned above, the bent valve broke the valve guide boss. The repair cost this: $90 for the valve job to one head; $50 to weld the guide boss; $12 for the valve guide; $40 for two Ti retainers (sold in pairs only), and $12 for the valve for a total of $204.
I'm glad to here the car runs well. I thought it would. Good luck on the rest of the repairs.
I can kinda see it. A plug strap is small enough to get into all kinds of trouble, like between piston and cylinder if it tries hard enough (lol), but a big chunk of valve will just bounce around and HOPEFULLY get blown out the exhaust. Or get caught, bend a valve or hang one open, or just get pounded into the piston. If you're lucky....
Sums it up lol.
The valve that broke was an exhaust valve so the chunk may have never even gone in the cylinder, it may have gone straight out the exhaust the second it broke. I still have the valve, and I come across it in the house tool box every once in a while and laugh.
The valve that broke was an exhaust valve so the chunk may have never even gone in the cylinder, it may have gone straight out the exhaust the second it broke. I still have the valve, and I come across it in the house tool box every once in a while and laugh.
11-21-2018, 08:26 PM
Stock LS6 Piston, head, and valve damage, unexpected 
