Is this piston defective or usable?

[averagejoe]

So I recently took apart a Gamo Carbine 640 that has sat for the last ~12-14 years because I thought it had a broken spring. After a few shots it became very crunchy and I could have sworn the barrel flopped down an inch when cracked which is why I decided to chuck it in the back of the safe and promptly forgot about it. I brought it out and it wasn't crunchy any more and there was no flop. Maybe the spring came out of the bind it was in?

I noticed that the end of the piston on the inside of the seal seems to have been smooshed during manufacture. It leaves a gap on the inside of the seal and stands proud, around level with the top of the seal instead of below like the rest. Is this something to worry about? Can I just file it flat with the rest and go about my day or will it need to be replaced because of that gap? I noticed that there is a slight mark on the face from the compression chamber because of it.




And the spring left a lot to be desired. One end was closed and ground flat, this was the other end. I am guessing that was the cause of the binding.

[TriggerHappy416]

The shape is of the piston end is important to hold the seal in place.

It's salvageable for sure. I think you can try carefully hammering the raised part back down to the original shape. Then lightly sand down any burrs.

For the spring end, I see a lot of them come from the factory like that from non-premium brands 10+ years ago. Just polishing down the rough edges will be fine. If you can heat and bend the end of the wire to be perfectly square and and grind to a flat surface, that would be be the best solution. Here's a picture for reference.

[Dukemeister]

I concur with TH416, peen the dovetail end flat and file level, grind smooth. Since the end doesn't contact anything the surface finish is mot important, jut try to get the profile back to true shape. How it got like that is a mystery, but probably happened outside the gun. That spring is a mess. You can dress it as suggested, or just replace it with a decent spring. Springs is cheap.

[averagejoe]

The shape is of the piston end is important to hold the seal in place.

It's salvageable for sure. I think you can try carefully hammering the raised part back down to the original shape. Then lightly sand down any burrs.

For the spring end, I see a lot of them come from the factory like that from non-premium brands 10+ years ago. Just polishing down the rough edges will be fine. If you can heat and bend the end of the wire to be perfectly square and and grind to a flat surface, that would be be the best solution. Here's a picture for reference.

I concur with TH416, peen the dovetail end flat and file level, grind smooth. Since the end doesn't contact anything the surface finish is mot important, jut try to get the profile back to true shape. How it got like that is a mystery, but probably happened outside the gun. That spring is a mess. You can dress it as suggested, or just replace it with a decent spring. Springs is cheap.

Alright, thanks, I just wanted to make sure it was fine to save it. It looks like it got damaged during manufacturing. Possible when it was crimped into the end of the piston tube, it would take a lot of force to damage it like that.

I already have a spring and replacement seal thankfully. The spring has both ends closed and flattened nicely.

There was molly on the spring but the piston tube was slathered in silicone grease. It ran down the tube and covered everything else. Can't complain for $60 back in 2008 I guess New spring is getting molly and the seal is getting Krytox since a friend sent me a tube years ago.

[Daryl]

Your spring was made like that. It did not become damaged through shooting it.
I would replace it.

[averagejoe]

Your spring was made like that. It did not become damaged through shooting it.
I would replace it.

Yup, well aware. Somebody hit it with a grinder at the factory and didn't finish the job. Once I opened it up I figured that was why it suddenly started binding after a low amount of shots and getting crunchy. Given how one part was partially cut through it likely would have broke off sooner than later. Spring and piston seal have been replaced.