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sr71bb · 08-13-2023, 10:19 PM

In post 336 above, you will see where I mentioned I cracked a piston in the number one cylinder. The pic below shoes the top of that piston as you are looking down the hole. You will notice there is a lateral crack all the way across thru the valve reliefs

When this happpened the piston rocked in the bore and there was some scarring just in the cylinder bore. A STOCK LT1\LT4 has 4.065 diameter pistons. When LME built this motor they used 4.070 pistons so that they could make all of the cylinder walls perfectly true by using a boring bar to enlarge the bore to 4.070.

Now the reccomended maximum bore on these engines is 4.080. So if the cylinder wall needs to be bored LARGER than 4.080 then the block is unusable. From a visual inspection, 4.080 looks like it SHOULD be fine.

A cracked piston can be cause by a couple of different things. DETONATION is ONE of them but that is highly unlikely in this case since this car is run exclusively on E85.

A second common cause of piston failure is called HYDROLOCK. This can occurr when liquid gets in the cylinder and since liquid WILL NOT compress then damage occurrs when the piston tries to push thru the liquid which basically had no path to go. This can occurr for instance if a head gasket fails allowing coolant to get in the cylinder bore. Another cause to be excessive fuel in the cylinder bore which can be caused by an injector that hangs open for some reason.

The head gasket looks fine and this engine is fully studded so head gasket failure is OUT. As far as hydrolock due to excessive fuel goes, that also appears unlikely.

SO basically I cant determine WTF happened but I will say it is HIGHLY unusual to crack a piston in an NA motor.

So I will mark this down as "SHIT HAPPENS"

Racing this car in 104 degree heat probably doesnt help things either LOL

UPDATE 8/20

Looking at the piston after removal we noticed the piston WAS NOT cracked all the way thru so it was still in one piece. The top ring DID close up at the ring gap and butted together. The damage to the cylinder wall looks to be superficial so it looks like we may be able to use another 4.070 piston with a fresh set of rings but we will confirm that next week.

08-13-2023, 10:19 PM	#339
sr71bb Drives: 2019 Camaro Z-28 Join Date: Jul 2010 Location: Dallas Posts: 1,512	Diagnosis Number ONE piston In post 336 above, you will see where I mentioned I cracked a piston in the number one cylinder. The pic below shoes the top of that piston as you are looking down the hole. You will notice there is a lateral crack all the way across thru the valve reliefs When this happpened the piston rocked in the bore and there was some scarring just in the cylinder bore. A STOCK LT1\LT4 has 4.065 diameter pistons. When LME built this motor they used 4.070 pistons so that they could make all of the cylinder walls perfectly true by using a boring bar to enlarge the bore to 4.070. Now the reccomended maximum bore on these engines is 4.080. So if the cylinder wall needs to be bored LARGER than 4.080 then the block is unusable. From a visual inspection, 4.080 looks like it SHOULD be fine. A cracked piston can be cause by a couple of different things. DETONATION is ONE of them but that is highly unlikely in this case since this car is run exclusively on E85. A second common cause of piston failure is called HYDROLOCK. This can occurr when liquid gets in the cylinder and since liquid WILL NOT compress then damage occurrs when the piston tries to push thru the liquid which basically had no path to go. This can occurr for instance if a head gasket fails allowing coolant to get in the cylinder bore. Another cause to be excessive fuel in the cylinder bore which can be caused by an injector that hangs open for some reason. The head gasket looks fine and this engine is fully studded so head gasket failure is OUT. As far as hydrolock due to excessive fuel goes, that also appears unlikely. SO basically I cant determine WTF happened but I will say it is HIGHLY unusual to crack a piston in an NA motor. So I will mark this down as "SHIT HAPPENS" Racing this car in 104 degree heat probably doesnt help things either LOL UPDATE 8/20 Looking at the piston after removal we noticed the piston WAS NOT cracked all the way thru so it was still in one piece. The top ring DID close up at the ring gap and butted together. The damage to the cylinder wall looks to be superficial so it looks like we may be able to use another 4.070 piston with a fresh set of rings but we will confirm that next week. Attached Images __________________ __________________________________________ 2019 SS 1LE BIG NA A10 Eagles Canyon Raceway 2.7 CCW Below https://youtu.be/c9M5UHDftcA 4-15-23 at SCCA TT U1 Class MEGA Thread on THIS car: https://www.camaro6.com/forums/showthread.php?t=602092 Retired Cars BELOW: 1973 Camaro, 1969 Camaro, 1969 Camaro SS RS 2010 Camaro SS with 1000HP F1R, 2019 ZL1 1LE A10 Last edited by sr71bb; 08-20-2023 at 10:19 AM.