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C6 Corvette ZR1 & Z06General info about GM’s Corvette Supercar, LS9 Corvette Technical Info, Performance Upgrades, Suspension Setup for Street or Track
Perhaps my earlier thread was not adequately titled, so I have changed it for the better. My 2008 LS7 engine had the heads and valves changed at 13500 miles because it was out of tolerance in only 13500 miles. This was handled by Chevrolet warranty and I was assured that the problem was solved. Now, 15000 miles later, I find that the replacement heads and valves are out of tolerance again. Four intake valve guide clearances are already out-of-tolerance and the other four intake valves are already at the manufacturer's limit. Here are the measurements performed by AHP: (Any measurement over .008" is considered to be out of spec. ) 1 int: .008 1exh: .006 3 int: .008 3exh: .006 5 int: .009 5exh: .007 7 int: .009 7exh: .006
So the issue I raise is when, exactly, did GM fix the problem? While GM claimed to fix the problem much earlier through 100% inspection of their subvendor, the problem was still clearly present through early 2013.
Those of you with later C6Z06 cars and other LS7s, this is another wake up call.
Does anyone know if the 427 Camaro's are having this issue?
Here are my measurements at 75,000 miles, interesting how 2,4,6,8 are all within spec and 1,3,5,7 are out of spec. Could this be that the one head came off of the "bad" fixture and one came off of the fixture that was set up correctly. ??????
There is a specific reason the odd side is worst and I think there is more complete failures from one of those but I can’t speak intelligently on why or which one has a higher fail rate, someone on here will probably chime in and have a good answer as to why. Here’s my data from Khole@AHP on the wiggle of the core I sent back. 16k miles but the car has a good bit of mods for 4-5k of those miles and the idiots didn’t do any of the supporting valve train upgrades needed. So mine aren’t a good set to compare against.
Does anyone know if the 427 Camaro's are having this issue?
Here are my measurements at 75,000 miles, interesting how 2,4,6,8 are all within spec and 1,3,5,7 are out of spec. Could this be that the one head came off of the "bad" fixture and one came off of the fixture that was set up correctly. ??????
Im not sure on the Camaro but I don’t see how they wouldn’t have issues as well, same heads. If you want some good data and review search threads by “Mordeth” or find his “winter mod” thread. Dude is an awesome guy, he’s got AHP heads and all the works. His vette is a dedicated race car and pretty much only see WOT driving. I believe he’s done two vale guide inspections and Khole’s MS90 are holding strong. Very pleased to see that especially since his car is pushed to the max when driven and he races that thing a lot.
There is a specific reason the odd side is worst and I think there is more complete failures from one of those but I can’t speak intelligently on why or which one has a higher fail rate, someone on here will probably chime in and have a good answer as to why.
I have read quite a bit on the subject. I do recall one of the articles that was written had said something to the effect that the company that had the contract to machine the heads had one of their fixtures set up incorrectly and the cylinder heads that came off of that fixture are the heads that cause the problems. Now, I'm not sure if this is true, but it is highly possible due to not ALL cars having the issue. Who knows!?
Does anyone know if the 427 Camaro's are having this issue?
Here are my measurements at 75,000 miles, interesting how 2,4,6,8 are all within spec and 1,3,5,7 are out of spec. Could this be that the one head came off of the "bad" fixture and one came off of the fixture that was set up correctly. ??????
Really? The issue with the heads is all 427 engines. Based upon anyone in hear that has dropped a valve or has valves out of spec. Mine were out of spec with only 4200 miles. The 427 in the camaro has the same problem you just don't here about as often because there are only a hand full of camaro's with a 427.
Really? The issue with the heads is all 427 engines. Based upon anyone in hear that has dropped a valve or has valves out of spec. Mine were out of spec with only 4200 miles. The 427 in the camaro has the same problem you just don't here about as often because there are only a hand full of camaro's with a 427.
Easy..... I know it's an issue, I just went through it. I'm just not sure EVERY 427 has the issue though. I thought maybe you had some information other than internet gossip.
Easy..... I know it's an issue, I just went through it. I'm just not sure EVERY 427 has the issue though. I thought maybe you had some information other than internet gossip.
Look not trying to be a D**k but do you really think it only effected some and not others? I doubt that very much. The ones you don't hear about are the ones where people have never checked the valves. Is it possible to have valves out of spec and not drop a valve, yes absolutely. Just becuase you don't drop a valve dosen't mean they are in spec. Any 427 should be at the very least be checked.
Look not trying to be a D**k but do you really think it only effected some and not others? I doubt that very much. The ones you don't hear about are the ones where people have never checked the valves. Is it possible to have valves out of spec and not drop a valve, yes absolutely. Just becuase you don't drop a valve dosen't mean they are in spec. Any 427 should be at the very least be checked.
I completely agree with you.
But it is possible to have multiple machines performing a task and one, (or more), to be programmed incorrectly causing an issue with certain pieces. Just saying....
We will never know for sure, but I would think that if EVERY head had the issue it would be a much bigger problem than it is.
Now the coating on the valve could be a whole other issue which I haven't researched.
Does anyone know if the 427 Camaro's are having this issue?
Here are my measurements at 75,000 miles, interesting how 2,4,6,8 are all within spec and 1,3,5,7 are out of spec. Could this be that the one head came off of the "bad" fixture and one came off of the fixture that was set up correctly. ??????
It's entirely possible. Some heads can live a normal life and stay "within spec", others are bad off the shelf from a guide-to-seat runout standpoint...which means they're doomed at birth. Its a crap shoot...
Originally Posted by TriSum1
I completely agree with you.
But it is possible to have multiple machines performing a task and one, (or more), to be programmed incorrectly causing an issue with certain pieces. Just saying....
We will never know for sure, but I would think that if EVERY head had the issue it would be a much bigger problem than it is.
Now the coating on the valve could be a whole other issue which I haven't researched.
There's been documented failure on Camaro Z/28's w/ the LS7.
Valve coating on the Ti intake is definitely a thing. GM told Del West "thanks, but no thanks" during C6 production years on the micro polishing step for the intake stem. Apparently, GM changed their stance on this for the C7 cars running Ti intakes. Hmmm...I wonder why?
I have researched this problem extensively and my 2011 currently has the heads off to do a repair. The one thing I can say with certainty is there is not one single problem causing the rapid wear on the guides and other failures causing the destruction of the engine, there have been a bunch of problems which is why there is no single magic bullet fix which is what I think a lot of people are expecting. The best and most promising repairs are either American Heritage Performance or Late Model Throttle which have both taken the time to have Moldstar 90 guides made for them. This appears to be a solution to the wear problem.
Known problems:
Machine problems on some heads
Titanium valves with too coarse of a finish on the valve stems
Exhaust valves with a strength problem so GM changed the wall thickness
Rocker arm bearing problems
Crappy pushrods
Failing camshafts probably due to failing valve springs
I have researched this problem extensively and my 2011 currently has the heads off to do a repair. The one thing I can say with certainty is there is not one single problem causing the rapid wear on the guides and other failures causing the destruction of the engine, there have been a bunch of problems which is why there is no single magic bullet fix which is what I think a lot of people are expecting. The best and most promising repairs are either American Heritage Performance or Late Model Throttle which have both taken the time to have Moldstar 90 guides made for them. This appears to be a solution to the wear problem.
Known problems:
Machine problems on some heads
Titanium valves with too coarse of a finish on the valve stems
Exhaust valves with a strength problem so GM changed the wall thickness
Rocker arm bearing problems
Crappy pushrods
Failing camshafts probably due to failing valve springs
Don't forget - piston rod thrust face damage!
The proper solution is to throw almost everything from GM in the garbage.
I have read quite a bit on the subject. I do recall one of the articles that was written had said something to the effect that the company that had the contract to machine the heads had one of their fixtures set up incorrectly and the cylinder heads that came off of that fixture are the heads that cause the problems. Now, I'm not sure if this is true, but it is highly possible due to not ALL cars having the issue. Who knows!?
GM has known for more than 5 years, but they aren't saying so they do not expose their responsibility. IMHO.
10-17-2018, 10:39 PM
2013 LS7 heads failing Valve Guide tolerances
