LBZ: Another broken piston. What's the cause ?

[McRat]

We have run 100,000 miles on our LBZ and it has been tuned it's whole life, has hundreds of drag passes, several sled events, as well as towing. It even had water dumped into the engine when the truck was stolen, and we tried to start it without knowing. Talk about hydrolock! It still has the original pistons (knock on wood).

I've seen virtually new LBZ's at stock power crack a piston, and I've put 936rwhp through a set and did not crack them.

The LBZ piston has pin bushings press fit into them. When you press a bushing into cast aluminum, there is always the risk of a crack forming. It's perhaps the most common cause for cracked aluminum heads, the crack often starts at the seats or guides.

Is there a process issue with the bushing install during production? Perhaps. But without extensive sampling and inspection using NDT methods, there is no way to be sure. Forgings are more resistant to cracks than casting methods and alloys.

 

[Dvierra86]

Not a minor detail haha. To each his own though.

Haha I know I'm not usually super hard on the trans in the bigger tunes knowing it's a time bomb at this point.


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[Awenta]

Stock trans is minor details haha. It's got the jr with Mike l springs and holds the 230tune quite well. It did not like the new turbo though


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I doubt that


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[malibu795]

We have run 100,000 miles on our LBZ and it has been tuned it's whole life, has hundreds of drag passes, several sled events, as well as towing. It even had water dumped into the engine when the truck was stolen, and we tried to start it without knowing. Talk about hydrolock! It still has the original pistons (knock on wood).

I've seen virtually new LBZ's at stock power crack a piston, and I've put 936rwhp through a set and did not crack them.

The LBZ piston has pin bushings press fit into them. When you press a bushing into cast aluminum, there is always the risk of a crack forming. It's perhaps the most common cause for cracked aluminum heads, the crack often starts at the seats or guides.

Is there a process issue with the bushing install during production? Perhaps. But without extensive sampling and inspection using NDT methods, there is no way to be sure. Forgings are more resistant to cracks than casting methods and alloys.

Welcome back:thumb:

 

[Dvierra86]

I doubt that


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Honestly , it'll hold 132 on gps at wot 225k miles on trans all stock besides transgo jr and Mike l shift springs. It's hurting the trans every time but never hit limp mode and never thrown a dtc. Occasionally it'll stick in second coming up to a stop


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[IOWA LLY]

It will HOLD 132 mph......?????? And your on here asking why you broke a piston????

Stock transmission, 4094 turbo, pegged EGT gauge, and an idiot behind the wheel driving 132 f***ing mph.

You sir, are an idiot.


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[Dvierra86]

It will HOLD 132 mph......?????? And your on here asking why you broke a piston????

Stock transmission, 4094 turbo, pegged EGT gauge, and an idiot behind the wheel driving 132 f***ing mph.

You sir, are an idiot.


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When I did 132 it was stock turbo and 230 tune egt was 1700, I unstable I drive it like an idiot, not sure how it constitutes me as being one. I also never said I'm upset the piston broke I'm just curious what causes it. Boost egts or fuel timing. The transmission hasn't shown much evidence of failure I check the fluid level and condition and smell on a weekly basis due to I do drive it hard at times. Just noticed two different trucks same year break pistons within one week from another and the same turbo was on each truck when each engine broke piston. And honestly 132 wasn't that bad it got there pretty quickly if you stay in it. But back to topic piston failure not transmission failure


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[Dvierra86]

We have run 100,000 miles on our LBZ and it has been tuned it's whole life, has hundreds of drag passes, several sled events, as well as towing. It even had water dumped into the engine when the truck was stolen, and we tried to start it without knowing. Talk about hydrolock! It still has the original pistons (knock on wood).

I've seen virtually new LBZ's at stock power crack a piston, and I've put 936rwhp through a set and did not crack them.

The LBZ piston has pin bushings press fit into them. When you press a bushing into cast aluminum, there is always the risk of a crack forming. It's perhaps the most common cause for cracked aluminum heads, the crack often starts at the seats or guides.

Is there a process issue with the bushing install during production? Perhaps. But without extensive sampling and inspection using NDT methods, there is no way to be sure. Forgings are more resistant to cracks than casting methods and alloys.

You sir have been one of the few to give an actual answer. So is egts more of a culprit then fuel injection/timing ? Will running a bigger nozzle on a smaller hp tune be more safe vs a smaller nozzle on a larger hp tune ? I'm assuming the cyl pressures would be less with a larger nozzle inj vs a stock one


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[jnieberlein]

It will HOLD 132 mph......?????? And your on here asking why you broke a piston????

Stock transmission, 4094 turbo, pegged EGT gauge, and an idiot behind the wheel driving 132 f***ing mph.

You sir, are an idiot.

:roflmao::roflmao::roflmao::roflmao:

My piston let loose also just driving down road, upon tear down the manifold gasket was in wrong restricting flow which may have been the final straw, also discovered 2 others with hairline cracks

 

[McRat]

You sir have been one of the few to give an actual answer. So is egts more of a culprit then fuel injection/timing ? Will running a bigger nozzle on a smaller hp tune be more safe vs a smaller nozzle on a larger hp tune ? I'm assuming the cyl pressures would be less with a larger nozzle inj vs a stock one


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I run so much timing in my tunes that it makes baby Jesus cry.

And have melted enough pistons to bump Mahle's stock up 2 points.

The popular theory is to run big injectors and shorter duration with less timing. But people STILL crack pistons.

I have an LBZ piston on my bench (from a friend) that looks like it was cracked at the factory. Like new, just in two pieces. Probably superglue it back together and run it.

Note that melting, not cracking pistons, is what was my downfall each time I blew an engine up from piston damage.

 

[Dvierra86]

I run so much timing in my tunes that it makes baby Jesus cry.

And have melted enough pistons to bump Mahle's stock up 2 points.

The popular theory is to run big injectors and shorter duration with less timing. But people STILL crack pistons.

I have an LBZ piston on my bench (from a friend) that looks like it was cracked at the factory. Like new, just in two pieces. Probably superglue it back together and run it.

Note that melting, not cracking pistons, is what was my downfall each time I blew an engine up from piston damage.

Hmm so for 600whp would 30% over injectors seem plenty ? I'm not asking much and I know my trans will need help real soon just mainly concerned about the engine being it's twice the cost as a trans and I can always just drive around in a lower switch position haha


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[jnieberlein]

I had 60 overs in that neighborhood and they worked very well

 

[McRat]

I personally would not do another build using LBZ pistons. While I didn't crack them, there is always the risk. LLY/LB7 or aftermarket pistons. One less thing to worry about.

 

[Dvierra86]

I personally would not do another build using LBZ pistons. While I didn't crack them, there is always the risk. LLY/LB7 or aftermarket pistons. One less thing to worry about.

I'm leaning towards the fingers and having them ballance within .5grams and then take rotating assembly to machine shop for further ballance and call it a day. Living in cali makes it tough to be complaint yet still be within relms of clean air standards haha figure 600whp is plenty for this state and more then enough to be super fun to drive


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[ripmf666]

If you dont replace the rods while doing Pistons it's not worth doing. Just throwing money into the wind for balancing, bearings and gaskets to have a weak link to cost it all over again shortly down the road.

 

[Dvierra86]

If you dont replace the rods while doing Pistons it's not worth doing. Just throwing money into the wind for balancing, bearings and gaskets to have a weak link to cost it all over again shortly down the road.

I'm not turning the engine up anymore then it is now. And also don't have another $2000 for rods he'll I don't even have $300 to begin with haha


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[ripmf666]

I'm not turning the engine up anymore then it is now. And also don't have another $2000 for rods he'll I don't even have $300 to begin with haha


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Rather waist the funds you don't have on the race cart or finger Pistons, the balancing and all gaskets and bearings needed for what your saying you want to do.
Just get a replacement piston and put it back together and turn it down and drive like a Saint. 132 and high gets is your issue.

 

[Dvierra86]

Rather waist the funds you don't have on the race cart or finger Pistons, the balancing and all gaskets and bearings needed for what your saying you want to do.

Just get a replacement piston and put it back together and turn it down and drive like a Saint. 132 and high gets is your issue.

I'm trading labor and some spare items I don't use for the pistons. Only Reason I'm getting the pistons. And I'm just doing the balancing to help prevent any unwanted vibrations which could harm the crank. Just as a precaution. I'm not gonna turn up the engine anymore than it is right now just need to fix the weak leak and let it last for a while


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[Dvierra86]

And I don't mind labor in doing it again later for better stuff I just need it on the road and able to handle my right foot until I can save up for good stuff


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[zakkb787]

Wonder why anyone hasn't mentioned a cut set of lb7 pistons yet... or instead of forged rods why not just a stock set of rods.