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As far as I know, the LT2 engine has a good reliability record, but there has been a lot of news about the GM truck and SUV V8 engine failures due to crankshaft journal/bearing problems. Does anyone have any insight as to why failures of this type haven't translated to the LT2, and, for that matter, how confident can we be that the LS6 won't experience this issue?
As someone who has experienced an engine failure/replacement in my '24 Sierra AT4, the letter that GM sent me about the recall and extended warranty stated that some of the internal parts that were manufactured in a facility in Mexico were manufactured "out of spec" which caused the internal engine failure.
Although they are both 6.2 engines, they are very much different from each other. My best guess (and it's only a guess) is that the Corvette engines were simply lucky enough to have all their internal parts manufactured correctly. As mentioned above, I received a new engine under warranty and have been trouble free ever since.
How sure can we be that it won't happen again? We can't really. We just have to hope GM has a handle on this now with their new engines.
The LT2 has a forged crankshaft while I believe that the truck engines use a cast crankshaft. So different materials and I suspect machining process as well. FWIW, the LS6 also uses a forged crankshaft as well as forged rods.
The LT2 and the truck engines share a lot architecturally with the differences being in crank, camshaft, and intake due to the different purposes of said engine. Why the LT2 hasn't been caught up in the mess.
Do not get worried. The Cranks had bad chamfers on the oil holes. This was only some of the cranks and it was a supplier error.
Rest assured this issue has been fixed already and they just need to figure out what ones got the bad cranks and what ones didn’t. that is why this was so messy.
Do not get worried. The Cranks had bad chamfers on the oil holes. This was only some of the cranks and it was a supplier error.
Rest assured this issue has been fixed already and they just need to figure out what ones got the bad cranks and what ones didn’t. that is why this was so messy.
Yep, the large number of Trucks with "possible" V8 defects were between 2021 and 2024. Probable cause was resolved in later years. The Truck L87 6.2 Liter V8 had a cast iron NOT forage crank like the LT2 in Vettes. GM says machining errors and possible debris from their crankshaft vendor was the cause.
Wondered way the machining error was not caught? At least some speculation is the cause was cavitation due to a somewhat subtle "defect" of an excess chamfer of the crank oil to bearing inlet hole. When I checked, the info in a compelling video, found cavitation casued bearing defects is a known problem found with some racing cranks with excess oil inlet hole chamfer!
Below is a Pic I made after watching a compelling video by a group who took apart an engine that failed the GM "sound test." The bearing defects they found were similar to that reported with some racing crankshafts with excess oil hole chamfer. Best I can describe in a few sentences: It is caused by "cavitation" (essentially air bubbles) forming as the oil exists. Like foam in oil, under high loads, the bubbles collapse and oil losses some of its ability to keep the metal surfaces apart.
Upper Pic is what was shown in the video by independent folks who disassembled an engine that failed the GM "Sound Test." The lower is a better Pic than what I could get from their video BUT shows similar excess chamfer of the crank oil inlet hole.
My friend brought his GMC Denali with the potentially defective V8 to the dealer as GM required. They conducted the GM "Sound Test" where they listen with special tools to the engine operating. They can detect potential for failure and if found replace those engines. His (as I suspect a very high percentage) passed. They did change the 0W-20 higher mpg oil specified for the engine to Mobil 1 Supercar 0W-40 Corvette oil. Also changed the oil fill cap to show that is what is to be used in the future. GM also extended the warranty for the V8 engines involved, to 10 years, 150,000 miles.
Yep this is a detailed explanation of "cavitation" casued by excess oil hole chamfer on the crankshaft oil hole inlet:
Google AI: An excessive chamfer on crankshaft oil holes disrupts the fluid dynamics of the lubrication system, making the engine highly vulnerable to bearing cavitation. While a light, smooth chamfer is beneficial, going too large creates immediate mechanical and hydrodynamic problems.
Why it causes cavitation
Sudden Pressure Drop: The primary cause of cavitation is a rapid drop in pressure. When an oversized chamfer transitions into the oil hole, it causes a sudden expansion of the fluid flow path. This localized drop in pressure causes dissolved air in the oil to flash into vapor bubbles (hydrodynamic cavitation).
Air Bubble Implosion: As the crankshaft rotates, these bubbles are carried into the high-pressure zone between the journal and the bearing. The sudden increase in pressure causes these vapor bubbles to collapse (implode) violently, which sends out shock waves that blast away microscopic bits of bearing material.
Flow Separation: An excessively wide or poorly blended chamfer stops the oil from smoothly transitioning into the oil passage. The oil detaches from the wall, creating turbulence and voids where vapor bubbles can easily form.
Loss of Oil Pressure: Over-chamfering effectively increases the volume of the oiling pathway. Because there is a larger volume to fill, overall hydraulic pressure can drop, reducing the thickness of the vital protective oil wedge (hydrodynamic wedge) that separates the crank from the bearing
Pic I made after watching a Video by an independent group that disassembled a GM Truck engine that failed the "Sound Test." The bearing wear area they found matched what is found in racing engines with excess oil hole inlet chamfer.
SIDEBAR
My 1st experience with "cavitation" occurred in 1959 when in high school and built my 1st car, a '41 Ford Coupe Hot Rod. I replaced Henry's Econo 136 cid flathead called a V8 60 (for 60 hp) with a '50 Olds engine. Had the Ford Rad modified by blocking one water inlet on top versus two and same with the bottom outlet with only one on the oposite side bottom. The Radiator Shop also made it a 15 psi pressure rad. I watched as the owner pressurised and soldered any leaks as he increased pressure. Fitting a 15 psi neck and cap. Car ran cool around town and on a highway up to ~60 mph. But at sustained highway speed the engine temp slowly increased.
Brought the car to the radiator shop and described the issue. The owner asked what thermostat I was using. Said none as that that would be best. He smiled and said, you're cavitating in the water pump as the flow rate is too high at higher rpm causing air bubbles and inefficient cooling. Install a thermoset and it will be fine. I Did And It Was! BTW to get the low 60 hp original engine to power the car up hills it came with a 4.44:1 dif. Engine rpm at highway speeds was high!
Yep this is a detailed explanation of excess oil hole chamfer on the crankshaft oil hole inlet:
Google AI:
An excessive chamfer on crankshaft oil holes disrupts the fluid dynamics of the lubrication system, making the engine highly vulnerable to bearing cavitation. While a light, smooth chamfer is beneficial, going too large creates immediate mechanical and hydrodynamic problems.
Why it causes cavitation
Sudden Pressure Drop: The primary cause of cavitation is a rapid drop in pressure. When an oversized chamfer transitions into the oil hole, it causes a sudden expansion of the fluid flow path. This localized drop in pressure causes dissolved air in the oil to flash into vapor bubbles (hydrodynamic cavitation).
Air Bubble Implosion: As the crankshaft rotates, these bubbles are carried into the high-pressure zone between the journal and the bearing. The sudden increase in pressure causes these vapor bubbles to collapse (implode) violently, which sends out shock waves that blast away microscopic bits of bearing material.
Flow Separation: An excessively wide or poorly blended chamfer stops the oil from smoothly transitioning into the oil passage. The oil detaches from the wall, creating turbulence and voids where vapor bubbles can easily form.
Loss of Oil Pressure: Over-chamfering effectively increases the volume of the oiling pathway. Because there is a larger volume to fill, overall hydraulic pressure can drop, reducing the thickness of the vital protective oil wedge (hydrodynamic wedge) that separates the crank from the bearing
Pic made after watching a Video by an independent group that disassembled a GM Truck engine that failed the "Sound Test." The bearing excess ware matched what is found in racing engines with excess oil hole inlet chamfer.
This is one of many things that get spread wrong on the web.
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Yep this is a detailed explanation of "cavitation" casued by excess oil hole chamfer on the crankshaft oil hole inlet:
