FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: dozz302 on February 13, 2022, 01:08:56 PM
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I have a set of CJ flat top forged pistons that were fly cut just barely into the back side of the top ring groove, Could that be repaired?
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I would say that they are DOA. Sorry.
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Did it just nick the landing or is there a hole through to the inside of the piston? if there is no hole I would de-bur it and use it. It's the outside of the ring that seals as long as the ring is free in it's landing. But that's coming from a guy that used a hand held die grinder to cut eyebrows in flat tops with just a stencil and got away with it.
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If I’m imagining what has happened, 2 votes for DOA.
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Gas ports in pistons connect the top of the dome to the back side of the top ring groove. They assist in sealing by forcing combustion pressure to the top and back of the ring, helping the ring seal against the cylinder wall. If the cut is into the back side of the top ring groove, you might just consider it a partial gas porting job, and run them as is. I'd be more concerned with the thickness of the dome in the flycut area, you don't want that below about 0.200". If the pistons are thick enough there, you are probably OK as-is, if I understand the issue correctly...
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I certainly hope this is on the intake relief. Jay is correct about the "gas port effect BUT you have a short term chance of them surviving. Cylinder pressure will cause the area to flex during the combustion cycle and that WILL lead to the area cracking out "in time". In a drag race only application maybe 50 runs and POOF you will begin smoking. IF by some chance it is the exhaust side DO NOT attempt to run them and NO there is NO CHANCE of repair. The heat of the exhaust will melt the area very quickly. Welding is not an option as it distorts the ring land and anneals the area resulting in failure again.
You have some ashtrays unless you are very brave.
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I wouldn’t touch them, yes small gas ports to allow pressure to move, but that piston moving up and down, is going to load that area. Power stroke it will try to push on the ring land and intake the other way. Never mind a little detonation raising pressures, sorry to hear it but that’s a bit of a violent location IMO
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I will have to double check but I think it is strictly from the intake valve relief to the back side of the top ring recess. I don't think it really touched the top or bottom of the ring landing. It was not thru to under the dome. These are flat tops. I will take a closer look at the pistons and get back. They are not mine.
I see exactly what you mean by it may not really matter. The gas preassure is already hitting the top of the ring and getting behind the ring itself, which is all that small notch will allow gas to flow also. Any chance of oil some how being sucked up from below the ring on the intake stroke thru that small hole? (unlikely?)
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.................. you have a short term chance of them surviving. Cylinder pressure will cause the area to flex during the combustion cycle and that WILL lead to the area cracking out "in time".
The discussion of the effect in the exposure of the ring to combustion pressure is all very interesting but, I would heed the statement above! If one wishes a greater sum of responses from "the field" on this subject, just pose this inquiry to the 351C crowd as this has been an issue constantly recreated for decades there. ;)
Scott.
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I will have to double check but I think it is strictly from the intake valve relief to the back side of the top ring recess. I don't think it really touched the top or bottom of the ring landing. It was not thru to under the dome. These are flat tops. I will take a closer look at the pistons and get back. They are not mine.
I see exactly what you mean by it may not really matter. The gas preassure is already hitting the top of the ring and getting behind the ring itself, which is all that small notch will allow gas to flow also. Any chance of oil some how being sucked up from below the ring on the intake stroke thru that small hole? (unlikely?)
I GUARANTEE the piston will fail , it is only a matter of when. When vertical gas ports are drilled ( .043 hole) into the top of the piston , careful attention is paid to AVOID putting a hole in either of the two valve relief areas to prevent breakage. This is not a guess , this is from 30+ years in the piston industry and experience with the subject.
Randy
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+1 on Randy's comments.
They will fail.
Been there. Done that.
Nitrous will encourage quicker failure if applied....
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OK, well these were done years ago and that is why they are still in the boxes not used...they still look so pretty though.
Thank you for the experienced incite.
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Are they standard bore or oversize? Do you have the pins and rings ?