Post by: goin_up_river771 on August 14, 2017, 04:41:56 PM
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Post by: Flusher on August 14, 2017, 08:18:49 PM
In your first picture, pistons get really weak where the valve notch gets dangerously close to the top ring groove. A true blower piston will have a thicker top ring land to increase strength in this area and to keep the top ring running cooler. I like to blend a radius there where the two intersecting cuts form a sharp edge and create a stress riser.
Depending on your combination of parts, you could be over 9.2:1 static compression ratio. I think you have a cam where the intake lobe closes early, building a lot of cylinder pressure. Iron heads retain a lot of temperature in the cylinders. I bet you have a fairly high dynamic compression ratio. Even a little boost could throw it into detonation.
How much run time would you estimate? Did you clean the burn pattern off the pistons before you took these pictures? If you did not clean the burn pattern off, I don't believe that it is a lean condition because the pistons are so clean, like they were just solvent washed. I think there is a lot of liquid fuel present in the cylinders, during combustion, that is detonating at peak cylinder pressure ATDC.
I can't really see a cross-hatch pattern on the cylinder walls. There is definitely a ridge at the top of cylinders for not much run time. Your first picture looks like the cylinder cross-hatch has been completely worn off by the rings, possibly from fuel washing the oil out of the cross-hatch valleys. Is it possible that you hydrostaticly locked the cylinders just enough to break the piston? I'm not saying there is not a detonation problem though.
I would also check the rings for signs that the gap is too tight and if the ends of the top ring have butted.
Maybe these videos will help:
https://youtu.be/Q1mRCNmYmGM
https://youtu.be/B5Zo0QN4Atc
Good luck,
Joe
Post by: goin_up_river771 on August 15, 2017, 04:37:30 PM
Looks like the results of detonation. I see a lot of pitting on the pistons. I bet you will see a lot of "peppering" on the ceramic of your spark plugs where molten aluminum from your pistons has transferred to the plugs.
In your first picture, pistons get really weak where the valve notch gets dangerously close to the top ring groove. A true blower piston will have a thicker top ring land to increase strength in this area and to keep the top ring running cooler. I like to blend a radius there where the two intersecting cuts form a sharp edge and create a stress riser.
Depending on your combination of parts, you could be over 9.2:1 static compression ratio. I think you have a cam where the intake lobe closes early, building a lot of cylinder pressure. Iron heads retain a lot of temperature in the cylinders. I bet you have a fairly high dynamic compression ratio. Even a little boost could throw it into detonation.
How much run time would you estimate? Did you clean the burn pattern off the pistons before you took these pictures? If you did not clean the burn pattern off, I don't believe that it is a lean condition because the pistons are so clean, like they were just solvent washed. I think there is a lot of liquid fuel present in the cylinders, during combustion, that is detonating at peak cylinder pressure ATDC.
I can't really see a cross-hatch pattern on the cylinder walls. There is definitely a ridge at the top of cylinders for not much run time. Your first picture looks like the cylinder cross-hatch has been completely worn off by the rings, possibly from fuel washing the oil out of the cross-hatch valleys. Is it possible that you hydrostaticly locked the cylinders just enough to break the piston? I'm not saying there is not a detonation problem though.
I would also check the rings for signs that the gap is too tight and if the ends of the top ring have butted.
Maybe these videos will help:
https://youtu.be/Q1mRCNmYmGM
https://youtu.be/B5Zo0QN4Atc
Good luck,
Joe
I probably have 10-12 hours on the motor and the pistons look exactly the same as when I pulled the head no solvent washing just wd40 the cylinder walls with a rag. The cam spec is a HR 620 lift 235 duration 112 LSA.. pistons are SRPs I'm thinking about changing all of them. I was thinking I shot my self in the foot with low octane. On this trip I had half tanks of month old gas topped if off with 91 then threw this Lucas oil octane booster in that I've never used.
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Post by: goin_up_river771 on August 15, 2017, 04:38:24 PM
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