Is this piston still useable?

[1slow2door]

I pulled the head on my car after a valve dropped (after a full head rebuild last year). The valve whacked it a few times so I guess it's really unuseable but I want to make sure anyways rather than having to tear everything apart again. The valve is bent, but it stayed together. There is also some metal "dust" in the bore which I'm guessing came from the piston and would need to be cleaned.

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[jrohner]

I would sand it smooth and keep using it.

 

[velocitysport31]

You really dont have to sand it smooth, it will be fine just slap your new head on and rock it.

 

[Redwidow]

You really dont have to sand it smooth, it will be fine just slap your new head on and rock it.

You need to sand it smooth so that any little burs dont get hot and burn off and end up going through your turbo.

I would just sand it as smooth as you can and reuse it. No issues there

 

[donniekak]

Most of the time when you bend valves they are nicked, but ok. The damage to that one looks more severe. I bet the ringland is pinched onto the ring. I would at least pull it and check the ring groove for deformation.

 

[99gst_racer]

You really dont have to sand it smooth, it will be fine just slap your new head on and rock it.

If you don't sand it smooth, then the high spots of those indentations will become hot spots on the piston, and that could lead to pre-ignition (detonation).


OP - It's difficult to be sure without close-up pictures, but it does look like it will be fine to use as long as you sand it smooth.

 

[BigBeans]

In the second photo the cylinder wall looks really sketchy.

Is that just the picture?

 

[GooeyGus]

In the second photo the cylinder wall looks really sketchy.

Is that just the picture?

I think the "bad spots" on the cylinder wall are actually just reflections of the top of the piston

 

[1slow2door]

Thanks for the responses everyone. Dumb noob question, but so in order to sand it, what would I have to do? Do I just go at with sand paper and flatten out the chipped portion? Or is it something that needs to be done professionally? I also forgot to originally mention that the pistons move up and down without an issue while turning the crank, so would the rings/lands be screwed up? I tried getting better pictures, but this is about all I could come up with. The dark one kind of shows how deep it is.

BigBeans - There's some oil that leaked out of the HG, and there is some tiny metal flakes in there (that I think would clean out easy), but it looks ok in person.

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[Long Duk Dong]

A couple of notes of interest here. One is that I would recommend sanding any and all sharp edges as smooth as possible or you risk creating hot spots in the cylinder and creating pre and or post detonation. Two is that one of the gouges appears to be on or near the crown of the piston. I can say that I have sanded smooth blems in pistons such as those before and have gotten by BUT I have had a couple come apart (One in a Novi 2000 302 and the other in a N2O 350.) after doing so as well do to stress fractures that I didn't notice. I have done them in the block with a dremmel. If you choose to go this route make sure to tape everything else off as best you can. Get the piston at top dead center before working on it and make sure to use a good shop vac. and blow everything out as best you can. Do not forget to change the oil as well and check the filter for any metal after the next oil change. Hope this helps.

 

[danl]

Since those are stock cast pistons and the force is really close to the edge of the piston the chances are good that the top ringland may be cracked. I would replace it. Its really not a huge deal to find another stock piston to press onto your rod. You can even reuse the piston rings on that piston if they are fairly new and still have "spring" to them. If you want hit that cylinder with a 3 stone hone for about 30-60 seconds with kerosene or wd-40.

If you do have a crack in that top ringland, and heat gets to the top ring, the piston will melt into the ringland, build up into the ring and ringland gap area, and gouge the cylinder wall. That block looks way too nice to chance doing that to it.

 

[BigBeans]

Is there any scoring or scratches on the cylinder wall, or just metal flakes on the surface?

 

[1slow2door]

No, it looks pretty clean. Just some flakes on the surface. The crosshatch from the factory is still there, although not as clean as the other pistons.

Danl - It's a pretty much stock (minus BSEK and a lengthy cleaning/painting last year) 140k block/pistons. So maybe I should pull it to see if anything else is messed up? Is there any way to check the ring without pulling it?

 

[BogusSVO]

drop the pan and pull the piston.... as hard hit as it looks I would have to agree with others that have posted, and check for pinched rings.

pinched rings are fairly common in the 4g that has bent valves.

if the rings move smooth in there lands then buff the piston with sandpaper or a flapper wheel and drop it back in...

I would not try to sand the piston in the block, grit can/will be left between the block and piston causing block wear and/or ring wear.

 

[99gst_racer]

Is it safe to say that if the top land if pinching the top ring, that the piston is garbage? Or is there a fix for that?

 

[BogusSVO]

if its pinched, you can try to run the proper sized ring groove cleaner bit thu it.....

personaly.. id junk it and replace it... but have the shop to a weight match of the old piston to the new one


I am sure one of the vendors here will have a single piston they would sell....

I doubt this is the first time it has happened.....

 

[white92talontsi]

There is something you all are over looking here. Whenever you have piston to valve interference you end up ruining Rod bearings. What happens is when the pistin contacts the valve it displaces the oil around the bearing. This in turn will slightly mushroom the bearing.

Personally if it were me I would drop the pan, pull the piston and check the ring lands and the skirts real good. If everything looks good there then I use these anytime I have to deburr the top of a piston.

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Replace the rod bearings on that cylinder and call it a day.

The last 4g63 that I had to pull the head on due to a jumped T-belt ended up coming back a month later because it ruined the rod bearings.

I wouldnt put it back together with the old bearings.

Also it may be the picture throwing it off but if you look closely at the 3rd pic you can see that it appears that piston is no longer sitting square in the bore. It is sitting closer to the wall on the side the valve contacted it. If its like that then i bet the ring land pinched the ring in the groove. Chances are the skirt may have been damaged on the opposite side if where the valve contacted.