Can a slightly bent ringland be repaired?

[stidnam]

I have got a set of forged pistons that one piston has a small slight bend in the ringland I guess from being dropped. Can this be bent back so that they can be reused? Pistons were very hard to acquire so would like to use them if possible.

It looks worse than it is as the bend is right near/on the gudgeon pin hole so the lower arch you can see in the pic is mostly from the gudgeon pin hole. Compare the right side of the pin hole with the bent bit on the left to see the raised bit. The ring width is 2.5mm

I thought that maybe it could be bent back with a press applying pressure on the bent spot only. Alternatively can this high spot be safely machined down without bending back? As this is the oil control ring there shouldn't be much compression forces on it right?

[fixeruperer]

how much is one piston ? id seriously weigh it up.

sure you could fix it, but you would have to stick it in a lathe and check that nothing is protruding, there is not much material there to begin with and is only going to get weaker, and when warming up it could grow unproportionally to the rest of the piston. that lil dent is going to be in the back of your mind for ever.

i, my self, would replace the piston. especially if its something im going to lean on.

[Daddio]

I'd take the high spot off with a needle file...even filed down its no thinner than the adjacent machined bit over the gudgeon pin so any worries about thermal expansion are really unfounded. After you have cleaned off the lump, check you have a nice smooth surface (polish off with ultra fine diamond needle file...dont use wet n dry cos it will not end up flat.) and the ring land is flat...maybe put the oil control ring in and make sure it can turn in the ring land without binding (rings rotate in the lands in use). I wouldnt try pressing it down for fear of fatigue (plus press tooling to get in there would be hard to find) but if you have access to a skilled machinist, a lathe will do just as well as the needle file IF set up right with the right tool.

Edit: Guarantee no one would bat an eyelid at filing the ring ends to correct ring gap, I dont see why fixing this minor issue would be so different?

[fixeruperer]

im just over cautious. maybe the normal cut out groove from the gudgeon mixed with the dent is scaring me (as said "looks worse than what it is") that shit just plays over in my mind haha.
ive repaired pistons before, but never the ring lands. and never in something im gonna lean on.

better yet, take it to a engine recon machine shop, and see what they say.

[trd_st184]

I'd be particularly worried that the ringland would have been pushed outwards, depending on the level it could scratch or prematurely wear the cylinder block.

For me i'd prefer the piece of mind knowing that there were no prior issues, but you may find a machinist will be able to repair it. Especially when building up a motor. Could you possibly contact the manufacturer of the pistons to see if they can send a replacement with the same specs? For the money you'd no doubt be putting into it, i'd get a replacement. I'm sure the professional machine costs could come out to a similar amount to a replacement piston.


I'm sure it will all work out no worries either way

[Sam_Q]

if you fix this i suggest a crack test

[stidnam]

The ringland is not pushed out so that the piston is out of round in that spot. I was thinking of putting it in the lathe here at work and skimming down the high spot until it is flush with the rest of the ringland. I measured the thickness of the material to determine what would be left if skimmed down. The high spot is 0.5mm above the rest of the ringland. The thickness of the ringland in the middle of the gudgeon pin hole where it is at its thinnest is 1.1mm and increases to 2.1mm on either side. Now if it is ok to have the ringland at 1.1mm where the gudeon pin hole is then by skimming it the ringland on the side of the hole reduces in thickness by max of 0.5mm so would still be thicker than the 1.1mm. The only section where it may get thinner is in the middle of the gudgeon pin hole as it appears that the high spot starts at or just off to the left of the gudgeon pin hole so at worst the thickness of the ringland at the middle of the gudgeon pin hole reduces to 1mm.

The other thing I have considered is that the bent does not stay the same height for the depth of the ringland and the greatest high spot is the first 1.5mm in depth of the ringland and then bascially disappears. The ringland depth is 3.5mm so the outer 1.5mm would be weaker.

Reallistally though it is a very small area in the scheme of the total ringland and I couldn't see that it would have a large amount of pressure on it as it is the oil ring so I'm leaning towards trying it. If it was the first two ringlands then there would be no question in my mind and I wouldn't use them.

Last time I priced up getting a single piston via SPS it came out to be about $400 for one piston. As I don't know the exact specs of the piston sending it to Mahlee would mean an additional fee to work out the dimensions etc. As this is a piston from the group B 396e evolution motor (race/rally version of the 4tgte with the 84mm stroke) it is not exactly like the specs are widely available on the net.

Sam_Q not sure if you are referring to a crack test as is or after if I try to bend it back?

A few more pics to show the bend

Unbent other side of the piston



Bent side



Bent side from slight top down



Side shot of bend



Bottom side of bent area. It is the triangular section on the edge that you can see which is where the bend is.

[SHEPPO3930]

do note, most pistons aren't round! They are slightly oval when cold so when they heat up and expand, them become round (this is due to the non-uniform shape underneath the crown where the gudgeon pin goes. So be bloody careful when machining it in a lathe.

i don't see an issue with trying to fix it. and you may as well try and fix it before buying a new piston (if you can).

[Billzilla]

Get a new piston, it's not worth the worry.

[trd_st184]

Get a new piston, it's not worth the worry.

I think so too, for the cost and time of having to trip the engine apart again and repair any damage that may be caused if there was something wrong with the piston it'd be considerably more than the $400 for another piston.

I'd want piece of mind, the replacement unit would be sure to guarantee that. Be curious to see how it all goes though.

I wonder how the dent on the piston got there, its a pretty hard spot to create the damage if it was to fall.

[HAVABEER]

yep i'd defineitly go new piston

but if your going to machine it up i'd get someone who knows how to use a lathe properly to do it.
i only say that as your going to have to get it running true and on center and you'll probably have to grind up a parting tool thats undersize of the ring groove width and if its running out of round your going to hit the piston its self and affecting the sealing capabilities of your ring.

honestly if you can't get a new one easily take it to a machine shop and make them do it.

[dnegative]

Get a new piston, it's not worth the worry.

Depends if a new one can be found
But, it is only the ring land for the oil ring so its not under the same stress as the first compression ring, if it could be fixed to a half decent standard maybe give it a go.