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That is a very unusual engine failure. Is there bad scoring of the bore?

Not sure yet but I will let you know when I pull the head off.

i've heard of this happening in LS motors as bit, this is what i used for my ring gaps.

Hello,

Failure of pistons can result due to incorrect ring gap. However, this all depends on the environment and the construction of the piston and rings. If the ring does bind then most of the time the ring will break. If the ring lans are worn then the ring will become wavey before breaking but there will also be sealing issues with the cylinder.

If the ring break into a small enough fragment then it can get trapped between the cylinder wall and the piston scoring the bore and marking the piston. The worst I have seen is that the edge of the piston breaks off and exposes the centre of the piston. Now you have a hole in the piston and fragments being smashed up into the head. Ring gap is important, particularly in the newer engines these days with some much differing in the metal type department. I know of one engine builder that will weld the cylinder liners to the block on an LSx motor to stop the liner walk you get with high horsepower.

However, it is all good to summise what has happened. It is far better that you tear it down and look at the evidence then work a solution. I remember years ago when I found a 4.2 VC SLE. motor dead. Guy sold it cheap because it "threw a rod" but the motor was still together and there was no vent hole. Did a compression test and cylinder 7 was non-existant so know the problem cylinder. Got the car home and turn the motor over by hand, everything felt good. tried to start the car (yes knew needed to be careful) and yes fired but sounded like a rod.

Pulled the pan off to have a look and found all rods intact. Then moved onto pull the head. Failure was obvious. Cylinder 7 had no piston. what had happened is that the crown of the piston broke around the oil ring lan and then came completely off. the rod then pushed this up into the head and flattened the crown to the shape of the combustion chamber, the valves had punched through the piston as well, luckily the rockers etc had not broken. I did rebuild this motor and it was a amazing little v8 afterwards. So pull it down with lost of pics and find the true failure and work from there.

Sad to hear you had an issue. Now is the time to pull stumps and fix it properly.

Cheers
oldn64

Holden202T wrote:i've heard of this happening in LS motors as bit, this is what i used for my ring gaps.

Thanks Sam, I will definitely use that. Using my bore an increase of 0.004" of ring gap looks about right assuming the ring gaps aren't too tight to start with.

oldn64 wrote:Hello,

Failure of pistons can result due to incorrect ring gap. However, this all depends on the environment and the construction of the piston and rings. If the ring does bind then most of the time the ring will break. If the ring lans are worn then the ring will become wavey before breaking but there will also be sealing issues with the cylinder.

If the ring break into a small enough fragment then it can get trapped between the cylinder wall and the piston scoring the bore and marking the piston. The worst I have seen is that the edge of the piston breaks off and exposes the centre of the piston. Now you have a hole in the piston and fragments being smashed up into the head. Ring gap is important, particularly in the newer engines these days with some much differing in the metal type department. I know of one engine builder that will weld the cylinder liners to the block on an LSx motor to stop the liner walk you get with high horsepower.

However, it is all good to summise what has happened. It is far better that you tear it down and look at the evidence then work a solution. I remember years ago when I found a 4.2 VC SLE. motor dead. Guy sold it cheap because it "threw a rod" but the motor was still together and there was no vent hole. Did a compression test and cylinder 7 was non-existant so know the problem cylinder. Got the car home and turn the motor over by hand, everything felt good. tried to start the car (yes knew needed to be careful) and yes fired but sounded like a rod.

Pulled the pan off to have a look and found all rods intact. Then moved onto pull the head. Failure was obvious. Cylinder 7 had no piston. what had happened is that the crown of the piston broke around the oil ring lan and then came completely off. the rod then pushed this up into the head and flattened the crown to the shape of the combustion chamber, the valves had punched through the piston as well, luckily the rockers etc had not broken. I did rebuild this motor and it was a amazing little v8 afterwards. So pull it down with lost of pics and find the true failure and work from there.

Sad to hear you had an issue. Now is the time to pull stumps and fix it properly.

Cheers
oldn64

Thanks, yeah the other option is that a ring broke. The motor was shut down pretty quickly so hopefully the bore survived

heff0018 wrote:
Thanks, yeah the other option is that a ring broke. The motor was shut down pretty quickly so hopefully the bore survived

I would not be too stressed about the bore being scored. At worst you can sleeve the bore (it is not that expensive) an you get true straight fresh thickness none cast bore. They do work well and I have done a few now. One was my chev pistoned 202 block (but it was a frankenstein and was doen due to the frank nature of it)

You will have options, just post up when you tear it down so that we can see.

Cheers
oldn64

Holden202T wrote:i've heard of this happening in LS motors as bit, this is what i used for my ring gaps.

ring gaps.jpg

Did that sheet come with ACL pistons? sure looks familiar

nope got it with my SRP pistons.

Got the motor out and the pistons are intact and the bore is ok. I will take the pistons out tomorrow and see why there was no compression in cylinder 3. In the meantime here is a pic of the fuel system with th3 surge tank installed.