what would cause a piston to crack like this? fatigue or stress cracks or something else? still usable or needs replacing? the inside of the cylinder looks slick with no gouges.
The lines I see are not cracks. They are scores from something hard going through the hydraulic system. They don't show on the packing ring so one has to assume they happened in a past life. It looks like there are grinding marks all over the piston. It is worth checking on cost for a new one. The packing does the sealing and the metal is never supposed to tough the cylinder barrel but the piston does support the packing minimizing the amount of areas the bears the hydraulic pressure. If the machine is a toy, putting it back together with new packing is what most people would do. What does the wear ring look like?
I'd second what John C. says! Looks like old damage someone dressed off in the past. If bore in cylinder looks real nice I would assume tube was replaced at the time the piston was damaged. Like he says if a "toy" or low usage machine I would reuse it after doing a bit better job smoothing out things. If machine was mine That is what I would do. On the other hand if you are doing this as a repair for a paying customer who might come back at you a year from now and try to claim a failure at that time is your fault then I would show it to him right now and suggest installing a new piston! Just out of curiosity, why did you open up the cylinder? I'd be guessing the rod seals were leaking.
yes the seals was starting to leak,i repacked the other side about 2yr ago. wear ring doesnt show any damage
The rubber piston seal looks scratched to me, and not worn out from many hours. Take a good look at the inside bore of the cylinder and maybe post the best picture you can get of it.
The photos in the OP are telling you to "Look down the hole".......... When you do that I think you'll find the inside of the cylinder has more grooves in it than furrows in a ploughed field. The piston seal has scratches on it that, although they are not as deep, mate up exactly with the deep score marks on the piston. As others have posted above that cylinder has had a ****-load of something hard and unyielding pass through it at some point in its life. Whether that was recently or not makes no difference. The cylinder's probably toast.
i will admit it was getting dark time it got it pulled apart. i will look into the cylinder better today when the suns shining. i guess either way it will get repacked and see how long she last. i have owned the machine for about 4yrs and it has been seeping for a few months and finally just started a decent stream of fluid the other day.
As for the scratches on the seal ring, I would also be wondering if there is some rust on the cylinder above where the oring for the head seals and that is where the scratches came from on the removal of the piston. Do agree a good inspection of the bore is in order, sometimes the coating of oil will gloss over the scratches. Might have to wipe it down inside and then drop a light down in to see what it looks like. Try to take a couple pictures!
the seeping is from the rod seal, not this piston seal, so you'll have to look at the rod, and your hydraulic fluid to see why that was leaking. If you put this back together, at least look it over real well with light and no oil on the cylinder. You can hone out the scratches better than they are now and it might last twice as long next time...
Reach down in that barrel as far as you can reach. Drag your thumb nail around the circumference, anything that grabs your nail is your enemy. You'll definitely feel what you can't see. As you've already stated, it's yours, yer not beating it. I'm sure she'd be good for another go.
Go back to pic #1 in the OP. Is that some sort of pitting on the chrome of the rod or just bits of lint from an old shop rag sticking to it..? The rod doesn't look too clever to me.
Last pic is a tell all, those are file drags on the piston, has had a serious internal failure and gouged the crap out of it at some time. I'd be replacing that chunk of scrap.
I have reused worse pistons. If this is used on some farm hoe that only gets used 20 hours in a year, I would reuse it and go on. If my livelihood depended on the machine being in good order, I would be checking the barrel out. Who knows if it is even the original piston? or barrel?
Or even if the rod's straight ....??
Almost looks like someone used a big pipe wrench on that piston at one time.
thats just lint one the rod in the pics, there is no pitting or proud spots on the rod and only minor scratching. as for the bore i wiped it out and cant fell nothing inside that would have scored the piston like that. it is pretty slick with only couple scratches that i can see and dont fell no gouges or nothing to cut the seals up. im thinking maybe they swapped out the body when they had the failure and reused the piston maybe. i forgot my phone to take pics wheni put it back together, probly wouldnt have showed up good noway. but got it back together, guess time will tell how long it holds up but i didnt find nothing that made me scared of it. hydrualic shop said he has seen pistons worse, and to reusue it as long as the body is still good.
Did you check if the rod was straight..? That would be the only other roadblock to reassembly.
rod was straight
The important thing on re-assembly is to make sure the piston goes into the cylinder with the wide fiber section first, often the pistons on CAT rods can be fitted incorrectly, when the piston has just entered the cylinder enough to allow the cap to be fitted it's then best to bolt down the cap, as this does help keep things running true. tctractors
Great to see you post again!!!