Broken Piston tear down

[Dperreault]

[XFordGuy]

Good job so far!

[Dperreault]

Originally Posted by XFordGuy

Good job so far!

I know, anyone can take stuff apart but can it go back together? We will see.

[Jim Lembo]

That broken piston looks VERY familiar. What does the #7 Cylinder look like and also the combustion chamber and valves for #7,,,,,how did they fare when the pston broke?

[Dperreault]

Originally Posted by Jim Lembo

That broken piston looks VERY familiar. What does the #7 Cylinder look like and also the combustion chamber and valves for #7,,,,,how did they fare when the pston broke?

Surprisingly the cylinder wall is untouched. I was due a bit of luck after this disaster.

Here is a shot of the combustion chamber and valve tops.



The machinist said some of the nicks will come out in the when he machines the head.

[Jim Lembo]

Chamber looks almost identical to mine, shouldn't be too hard to clean it up.
While you got everything apart it might be a good idea to replace all your internal fasteners to ARP. (rod bolts and main bearing fasteners).
Are you going to get the heads done while they are off? Valve job, new seals/guides and maybe a slight milling to up the compression a bit? IMO, it would be money well spent and definitely enhance performance.

[Dperreault]

Originally Posted by Jim Lembo

Chamber looks almost identical to mine, shouldn't be too hard to clean it up.
While you got everything apart it might be a good idea to replace all your internal fasteners to ARP. (rod bolts and main bearing fasteners).
Are you going to get the heads done while they are off? Valve job, new seals/guides and maybe a slight milling to up the compression a bit? IMO, it would be money well spent and definitely enhance performance.

The heads are at the shop right now. 3 angle valve job and a mill on the faces. Surprisingly he checked out the valves and they were all straight. He's going to double check them since I dropped my old piston off to get pressed in to the control arm and seen the half moon mark in the crown.

I'm going to have my tuner bump the RPM down a couple hundred so we don't have this problem again.

[racingvette]

Originally Posted by Dperreault

The heads are at the shop right now. 3 angle valve job and a mill on the faces. Surprisingly he checked out the valves and they were all straight. He's going to double check them since I dropped my old piston off to get pressed in to the control arm and seen the half moon mark in the crown.

I'm going to have my tuner bump the RPM down a couple hundred so we don't have this problem again.

Rev limiter has nothing to do with the failure as stock is 6,600 and many of us run around 7,000 for years with no problems

As stated in your other thread on this I mentioned broken ring land as your #7 is proven to be due to bad tuning and too small of fuel injectors

Your pictures show this failed some time ago and driven that way over time

Being it was not tripping CEL and flashing for a P0300 says the old tuner turned off misfires function in PCM so real misfires were ignored by the PCM to prevent it from reacting to misfires and hence real misfires would cause out of timing of valve face kissing piston
You can bet they also detuned engine knock protection which would add to the piston slap damaging ring land.

Th past tuner was trying to hide/mask problems and caused the long term damage

Ring land breaks from that cylinder running way lean and causes cylinders temps to run way hotter over a good amount of time

If your thinking is reduce engine design by lowering rev limiter as protection to this failure assures it will happen again without doing as suggested several times in larger fuel injectors and then retuning for them

If rev limiter setting was the sole cause then ALL pistons over time would show at some point valve kissing piston top and possible the valve springs used were wrong for the CAM grind/lift and/or wrong length pushrods.

[Dperreault]

Originally Posted by racingvette

Rev limiter has nothing to do with the failure as stock is 6,600 and many of us run around 7,000 for years with no problems

As stated in your other thread on this I mentioned broken ring land as your #7 is proven to be due to bad tuning and too small of fuel injectors

Your pictures show this failed some time ago and driven that way over time

Being it was not tripping CEL and flashing for a P0300 says the old tuner turned off misfires function in PCM so real misfires were ignored by the PCM to prevent it from reacting to misfires and hence real misfires would cause out of timing of valve face kissing piston
You can bet they also detuned engine knock protection which would add to the piston slap damaging ring land.

Th past tuner was trying to hide/mask problems and caused the long term damage

Ring land breaks from that cylinder running way lean and causes cylinders temps to run way hotter over a good amount of time

If your thinking is reduce engine design by lowering rev limiter as protection to this failure assures it will happen again without doing as suggested several times in larger fuel injectors and then retuning for them

If rev limiter setting was the sole cause then ALL pistons over time would show at some point valve kissing piston top and possible the valve springs used were wrong for the CAM grind/lift and/or wrong length pushrods.

I understand what you're saying. Unfortunately, all of the pistons have been kissed by the valves some more than others.

So that's telling me that not only did the tuner turn off all of the warning codes but the RPMs were also too high for the springs in the valve train. Me and my buddy are going to try to determine the lift and duration of my Cam and make appropriate changes to the valvetrain if necessary.

I am also planning on bringing my fuel injectors to my tuner and having him pump them up to 36 pounds, after everything is put back together. I certainly don't want a repeat of this disaster.

On a different note. I really would like to pull the Billy boat bullets off my car as they are way too loud. If I put the stock titanium system on my Z would that caused a problem with airflow since I have long tube headers, high flow cats, and that high duration and lift cam?

[DucZ06]

Originally Posted by Dperreault

On a different note. I really would like to pull the Billy boat bullets off my car as they are way too loud. If I put the stock titanium system on my Z would that caused a problem with airflow since I have long tube headers, high flow cats, and that high duration and lift cam?

I would be interested to hear the response to this as I have been having the same question lately. Thanks for posting the pics, looks like it could have been a lot worse than it was.

[MikesZ06]

Originally Posted by Dperreault
On a different note. I really would like to pull the Billy boat bullets off my car as they are way too loud. If I put the stock titanium system on my Z would that caused a problem with airflow since I have long tube headers, high flow cats, and that high duration and lift cam?

Originally Posted by DucZ06

I would be interested to hear the response to this as I have been having the same question lately. Thanks for posting the pics, looks like it could have been a lot worse than it was.

As I told Dperrault in a pm, I don't believe the stock titanium exhaust restricts the air flow at all. If they did, you would see power gains with just aftermarket cat backs and you don't.

My suggestion is to slap on some Borla cat backs. Not nearly as rowdy as the BB's but a nicer sound IMHO than the oem. Some folks like the Corsa system too But I prefer the Borla's.

Mike

[racingvette]

Due to the fastburn head design for the LSx engines and even stock CATs today the flow is pretty good and not a lot of backpressure

So mufflers themselves will not produce more HP and brand/type of muffler is more about the quality of sound the owner likes.

What can be an issue is seeing the amount of carbon build up on your valves and piston tops that

1. past owner was lazy and never did common maintenance in using a good decarb cleaner

2. That tune and mods were not matched well forcing a too lean of condition that the PCM non stop could not correct the AFR and thus was dumping in more fuel when it was not needed and causing CATS to run too hot causing the PCM to trigger the CAT overtemp protection which was dumping in even more fuel to try and cool CATs down

End result of that along with carbon build up is caking up the CATs, (they might have even been breaking up and clogging the mufflers) and corrupting the O2 sensors.

As much as the junk said in cyberspace USE also the rear 02 sensors even if not using CATs as the GM PCMs use the rears for short term fuel trims and what average fuel injector pulse width ON times for each drive cycle.

You would be real wise at this point to make the effort and verify 02s, CATs and existing mufflers are in good working condition and best is to replace at least both front 02s.

If your looking for gains replace both CATS with a true X-pipe at that location thus existing exhaust pipes and catback can be used.
This will increase the low end torque and change the sound of exhaust.

As to catback change the thought would be weight saving as stock system is about 75 lbs and other designs can cut that weight in half.

Rev limiter reduction is not the fix, the path is use a pushrod length tester to assure proper length rods are used and better vale springs
The later beehive designs work well

Dual spring is more about harmonics of the thin inner spring and not as much to prevent valve float.

If you want to prevent end cylinders from being too hot/lean the coolant lines the LS1 had do just that by the flowing water pulls heat out or
install water methanol injection even with a NA engine will pull 40 plus temp degrees out of cylinders and is cheap in long term costs.

Decent kits are less then $500 and trigger off the MAF output signal so can be adjusted to flow only when in upper engine loads

Originally Posted by Dperreault

I understand what you're saying. Unfortunately, all of the pistons have been kissed by the valves some more than others.

So that's telling me that not only did the tuner turn off all of the warning codes but the RPMs were also too high for the springs in the valve train. Me and my buddy are going to try to determine the lift and duration of my Cam and make appropriate changes to the valvetrain if necessary.

I am also planning on bringing my fuel injectors to my tuner and having him pump them up to 36 pounds, after everything is put back together. I certainly don't want a repeat of this disaster.

On a different note. I really would like to pull the Billy boat bullets off my car as they are way too loud. If I put the stock titanium system on my Z would that caused a problem with airflow since I have long tube headers, high flow cats, and that high duration and lift cam?

[racingvette]

Originally Posted by DucZ06

I would be interested to hear the response to this as I have been having the same question lately. Thanks for posting the pics, looks like it could have been a lot worse than it was.

Would be smart is spending like $45 and places like Radio Shack sell a sound DBa test meter.

Consider the noise standard/laws, maximum DBa allowed is 94 Dba
With tester check other Corvettes at idle ( meter 45 deg angle to exhaust tips) using different muffler designs

If you want SAFE sound you want no more then about 82 Dba within drivers area. That would be safe for 8 non stop hours of driving
Every 2 Dba gain from that cuts down the maximum allowed time by half.

Once ears are damaged by high Dba there is no fix to repair hearing damage, just ask any of us hardcore racers :-(

If considering using a true X-pipe close to engine install that first with existing mufflers as sound will change and then decide on if another design of muffler is wanted.

A cheap fix is instead of replacing expensive catback is to install a bullet pre mufflers in drivetube area, they will not increase backpressure if good ones are used and will lower then DBa output of mufflers you have now.

[Dperreault]

Originally Posted by racingvette

Due to the fastburn head design for the LSx engines and even stock CATs today the flow is pretty good and not a lot of backpressure

So mufflers themselves will not produce more HP and brand/type of muffler is more about the quality of sound the owner likes.

What can be an issue is seeing the amount of carbon build up on your valves and piston tops that

1. past owner was lazy and never did common maintenance in using a good decarb cleaner

2. That tune and mods were not matched well forcing a too lean of condition that the PCM non stop could not correct the AFR and thus was dumping in more fuel when it was not needed and causing CATS to run too hot causing the PCM to trigger the CAT overtemp protection which was dumping in even more fuel to try and cool CATs down

End result of that along with carbon build up is caking up the CATs, (they might have even been breaking up and clogging the mufflers) and corrupting the O2 sensors.

As much as the junk said in cyberspace USE also the rear 02 sensors even if not using CATs as the GM PCMs use the rears for short term fuel trims and what average fuel injector pulse width ON times for each drive cycle.

You would be real wise at this point to make the effort and verify 02s, CATs and existing mufflers are in good working condition and best is to replace at least both front 02s.

If your looking for gains replace both CATS with a true X-pipe at that location thus existing exhaust pipes and catback can be used.
This will increase the low end torque and change the sound of exhaust.

As to catback change the thought would be weight saving as stock system is about 75 lbs and other designs can cut that weight in half.

Rev limiter reduction is not the fix, the path is use a pushrod length tester to assure proper length rods are used and better vale springs
The later beehive designs work well

Dual spring is more about harmonics of the thin inner spring and not as much to prevent valve float.

If you want to prevent end cylinders from being too hot/lean the coolant lines the LS1 had do just that by the flowing water pulls heat out or
install water methanol injection even with a NA engine will pull 40 plus temp degrees out of cylinders and is cheap in long term costs.

Decent kits are less then $500 and trigger off the MAF output signal so can be adjusted to flow only when in upper engine loads

Since I have decided to keep my Z. I just made the decision today to replace all the pistons with a flat head OEM spec after market replacement. This was a tough decision as I'm well over budget but in the long run it will be right. This will give me the best starting point with a fresh engine, just short of pulling the engine, which I'm not going to do. I'm happy with and in-engine Overhaul.

I'm going to get this Z to where it should have been when I bought it.

If you had $400-$500 what brand of piston set would you recommend? I plan on measuring the cylinder bore this weekend to make sure I'm within specs of an off e shelf piston.

Do you know the specs of our stock pistons. Unfortunately, all the number are Greek to me but my buddy mechanic will know.

Thanks.

[Dperreault]

Here's an update on my engine in-frame overhaul. I've decided to replace all eight pistons with a good set of forged pistons. My buddy is coming over Saturday and we are going check the bore stroke so we ensure we get the correct size pistons.

We are also going to try to determine the lift and duration of my existing cam . This will tell me whether or not I have the correct pushrods and also the proper springs in the valvetrain.

I am also replacing all four oxygen sensors just in case they were fouled by what racingvette was saying.

My heads are currently at the machinists getting milled and a 3 angle valve job. In the end I will have a brand-new engine when it's all said and done. I'm actually getting very anxious to get it all back together so I can see how she'll run

On a positive note, I did find a nice set of stock titanium mufflers a few hours away from me and I'm picking them up on Sunday. So my days of enduring the extremely loud bullet exhaust will come to an end.