SCAR17 piston cracking [Archive] - M4Carbine.net Forums

QuietShootr

01-19-14, 18:21

I did a detail strip on my SCAR17, and imagine my surprise when I started scraping the carbon off, and my tool FELL INTO THIS POTHOLE on the underside of the piston. I have 1722 rounds on the gun.

http://i950.photobucket.com/albums/ad346/QS762/public/IMG_1880.jpg

http://i950.photobucket.com/albums/ad346/QS762/public/IMG_1879.jpg

The gun functioned fine, I would not have discovered it until I detail stripped the gas system. I know FN will make it right, my experience with their customer service thus far has been superlative. Just throwing a data point out there.

HKGuns

01-19-14, 20:56

JPB

01-19-14, 21:15

Wow man, that's alarming. I can't see it in the pic, but I'll take your word for it.

QuietShootr

01-19-14, 21:18

That doesn't look good, in the picture it looks more like pitting than cracking, but that might be the light and/or the picture.

I wonder what their parts replacement schedule is on the piston? I would guess it to be north of 10K rounds.

ETA: You might also want to follow up with them on the proper cleaning method. I know on other similar systems it is recommended to use only a soft brush.....Not sure if that is the case here or not, but it is possible for aggressive cleaning to do more harm than good in some cases.

It's only been cleaned with a nylon M16 brush and Shooter's Choice, and that only twice. It's more than a simple pit, there is actually a chunk missing. Agreed, though. I'm not a big gas system cleaner. The rifle's only been cleaned three times.

ETA: The TRS says that the piston is to be replaced at 25,000 rounds - the rings every 5,000.

halmbarte

01-19-14, 22:29

Corrosion?

What kind of environment do you live in? Salt air?

H

G19A3

01-20-14, 01:18

From the pics, it almost looks like a porous casting defect. Is it possible it originally came that way new from the factory, and you missed it the previous two cleaning sessions?

Otherwise, did you inspect the rest of the gas system for similar "potholes?" I'm thinking one or three rounds of corrosive ammo.

m4carbine

01-20-14, 04:02

This is a first. Interested in hearing more on this one.

QuietShootr

01-20-14, 07:13

I did inspect it before, and this is new - which is why I started to go after it with a scraper. Up to this point I've only needed an M16 brush and SC to clean up the piston. I agree it does look like a casting defect. I have not knowingly shot any corrosive ammo, and I think if that were it, I'd see some orange around the gas regulator and front sight base.

From the pics, it almost looks like a porous casting defect. Is it possible it originally came that way new from the factory, and you missed it the previous two cleaning sessions?

Otherwise, did you inspect the rest of the gas system for similar "potholes?" I'm thinking one or three rounds of corrosive ammo.

G19A3

01-20-14, 07:28

I did inspect it before, and this is new - which is why I started to go after it with a scraper. Up to this point I've only needed an M16 brush and SC to clean up the piston. I agree it does look like a casting defect. I have not knowingly shot any corrosive ammo, and I think if that were it, I'd see some orange around the gas regulator and front sight base.

So it's not really cracked as it is "pitted?"

You sound like a very thorough person, but I will ask anyway. How does the rest of the rifle look internally...barrel, muzzle device, other parts near the gas block where the piston goes? Use a real good flashlight to inspect these areas.

QuietShootr

01-20-14, 07:35

So it's not really cracked as it is "pitted?"

You sound like a very thorough person, but I will ask anyway. How does the rest of the rifle look internally...barrel, muzzle device, other parts near the gas block where the piston goes? Use a real good flashlight to inspect these areas.

I just went and looked again. Just normal powder fouling and a slight amount of copper residue. I don't see anything abnormal.

VooDoo6Actual

01-20-14, 07:48

From the pics, it almost looks like a porous casting defect.

I seriously doubt that is a cast part. I would speculate forged. Appears to be grind / machining / friction surface anomalies.

G19A3

01-20-14, 07:50

I just went and looked again. Just normal powder fouling and a slight amount of copper residue. I don't see anything abnormal.

Did you check real well INSIDE the hollow chamber where the piston goes?

I don't own a SCAR, but I have couple of FS2000's which have an almost identical gas block as the SCAR...well at least the SCAR16. Once field stripped with the piston removed, I can see inside the little chamber. Maybe remove the adverse gas plug too, IIRC. It will probably be dark with carbon, so you may have to clean it out first. If something foreign chemically/physically did that to the piston, there may be clues to the "female" side of the "male" piston.

G19A3

01-20-14, 07:52

I seriously doubt that is a cast part. I would speculate forged. Bears some research.

May be, but the gas block is definitely cast, so it wouldn't be too much of a stretch if the piston is too.

halmbarte

01-20-14, 07:57

May be, but the gas block is definitely cast, so it wouldn't be too much of a stretch if the piston is too.

Different parts with different stresses. All the operating power for the rifle is transmitted by the small end of the piston smacking into the bolt carrier.

And the FS2000 uses almost the exact same design. If the piston was a cast part I would have expected failures to crop up before now.

H

G19A3

01-20-14, 08:05

Different parts with different stresses. All the operating power for the rifle is transmitted by the small end of the piston smacking into the op rod.

And the FS2000 uses almost the exact same design. If the piston was a cast part I would have expected failures to crop up before now.

H

I agree, and the piston and op rod would be hardened I would hope. But the OP's pics look like a casting defect. The pitting is localized to a small spot.

VooDoo6Actual

01-20-14, 08:10

May be, but the gas block is definitely cast, so it wouldn't be too much of a stretch if the piston is too.

Sure possible. I'd be surprised & disappointed if the piston is cast. They know better.
I'll check w/ my sources at FN & get back later.
No prob.

G19A3

01-20-14, 08:18

Sure possible. I'd be surprised & disappointed if the piston is cast. They know better.
I'll check w/ my sources at FN & get back later.
No prob.

Disappointed would be an understatement.

Please let us know. Thanks.

If indeed cast, I'm gonna have to order a couple or three extra pistons. Don't want what happened to the OP to happen to my FS2000's without spares. In fact, might be a good idea to order them anyways, cast or forged.

QuietShootr

01-20-14, 08:24

I did. Oddly enough for the internet, I do know what I'm doing - I have been run through the entire SCAR armorer's course by someone who knows his shit and services a large number of these guns every year. He has never seen this defect either. I'll take some more pics when I get a chance, but there's nothing abnormal about the gas block, gas screw, regulator, or anything else that I can see.

Did you check real well INSIDE the hollow chamber where the piston goes?

I don't own a SCAR, but I have couple of FS2000's which have an almost identical gas block as the SCAR...well at least the SCAR16. Once field stripped with the piston removed, I can see inside the little chamber. Maybe remove the adverse gas plug too, IIRC. It will probably be dark with carbon, so you may have to clean it out first. If something foreign chemically/physically did that to the piston, there may be clues to the "female" side of the "male" piston.

VooDoo6Actual

01-20-14, 08:25

Disappointed would be an understatement.

Please let us know. Thanks.

If indeed cast, I'm gonna have to order a couple or three extra pistons. Don't want what happened to the OP to happen to my FS2000's without spares. In fact, might be a good idea to order them anyways, cast or forged.

Typically, a MIM or cast part in that config would be cast longitudinally or lengthwise. One would see a mold / cast line running lengthwise congruently if the case. I haven't seen it on mine or in the OP's pic. Concentricity is pretty important on this part.
Surely would want to know.

COZ ZINZKI

01-20-14, 08:40

I never took my gas piston out to clean yet. I'll be watchfull for any fissures & or pits /cratering.
That is strangely abnormal for that to happen , running non-corrosive ammo.
Gonna try the magnet trick to get the piston out. (cleaning rod with jag-tip too ) I'll see which one I prefer.

Thanks for letting us know ,this can happen to a forged part..

VooDoo6Actual

01-20-14, 08:46

Found the part here & in stock etc.
http://www.midwestgunworks.com/page/mgwi/prod/scar-parts/F141200010
They don't stipulate it's attributes.

Probably the 2nd best source or one of & schematic out thus far.
http://www.midwestgunworks.com/page/mgwi/ctgy/scar-parts

QuietShootr

01-20-14, 08:48

Just put an old .22 bore brush on a cleaning rod and poke the piston out from the rear.

I never took my gas piston out to clean yet. I'll be watchfull for any fissures & or pits /cratering.
That is strangely abnormal for that to happen , running non-corrosive ammo.
Gonna try the magnet trick to get the piston out. (cleaning rod with jag-tip too ) I'll see which one I prefer.

Thanks for letting us know ,this can happen to a forged part..

VooDoo6Actual

01-20-14, 09:01

Spoke w/ my contact @ FNH USA Shanon @703.288.4507 ext 4
He says Piston in stock $31.00 & in his opinion it is a forged part.
he said he'd "never heard or seen problem before".

QuietShootr

01-20-14, 09:11

Spoke w/ my contact @ FNH USA Shanon @703.288.4507 ext 4
He says Piston in stock $31.00 & in his opinion it is a forged part.
he said he'd "never heard or seen problem before".

Is it OK to call him and order, then?

VooDoo6Actual

01-20-14, 09:22

Is it OK to call him and order, then?
Of course, you bet.

QuietShootr

01-20-14, 09:34

Of course, you bet.

That's a fax number, bro.

VooDoo6Actual

01-20-14, 09:43

That's a fax number, bro.

LOL good one. Early for me here. Need more Aviation Fuel for my motor.

Here ya go:
703-288-3500 Ext. 4
BTW, the're not closed just disregard recorded message & drive on through prompts to ext # 4.

QuietShootr

01-20-14, 10:04

Pistons are $65. :-P

LOL good one. Early for me here. Need more Aviation Fuel for my motor.

Here ya go:
703-288-3500 Ext. 4
BTW, the're not closed just disregard recorded message & drive on through prompts to ext # 4.

VooDoo6Actual

01-20-14, 10:07

Weird talked w/ him this morning he said $31.00. WTF ?
Strange times Dawg. Nothing in it for me being dishonest w/ you..... go figure...
Ask him why the difference since he knows I called & spoke with.

QuietShootr

01-20-14, 10:12

I didn't mean to imply that - the weird thing was that he said 16 pistons are cheaper, but the TRS says that's one of the common parts. Oh, well. They're $65 everywhere else, too.

Weird talked w/ him this morning he said $31.00. WTF ?
Strange times Dawg. Nothing in it for me being dishonest w/ you..... go figure...
Ask him why the difference since he knows I called & spoke with.

VooDoo6Actual

01-20-14, 10:14

I didn't mean to imply that - the weird thing was that he said 16 pistons are cheaper, but the TRS says that's one of the common parts. Oh, well. They're $65 everywhere else, too.

No sweat. I'd call him out on it.
If you want me to, I'll call him & hold his feet to the fire.....

Let's get all the liars by the fire...

still sucks..

QuietShootr

01-20-14, 10:22

No sweat. I'd call him out on it.
If you want me to, I'll call him & hold his feet to the fire.....

Let's get all the liars by the fire...

still sucks..

If you think it'll do some good for you to call, I'm not going to argue with you - that's half price :-P

ETA: I should have just said "Well give me the $31.00 piston, I'll make it work :-P"

ETA again: I want to make it clear to everyone that I am in no way disparaging FN's customer service. Their warranties are no-shit, they replaced an entire gun for me once.

VooDoo6Actual

01-20-14, 11:42

Ok so here's the lowdown on the dl,
Called him & after a the usual pass around the hot potato call back & forth & speaking to Rita, the waiting, & all the busy bs like no one on the planet isn't busy as well or understands what busy is, got him to return my call.
After no less than 3 deflections of the direct question & 3 re-directs to answer the original question of why the misquoted price he finally took ownership of it & said he made a mistake.
It took 3 re-directs on my behalf mind you to get him to actually answer the question.
Good guy, good service just get it in writing or email is all.

Stay frosty

QuietShootr

01-20-14, 12:29

thanks for doing that, man. I'm unclear though - is he honoring the price he gave you, then, or no?

Ok so here's the lowdown on the dl,
Called him & after a the usual pass around the hot potato call back & forth & speaking to Rita, the waiting, & all the busy bs like no one on the planet isn't busy as well or understands what busy is, got him to return my call.
After no less than 3 deflections of the direct question & 3 re-directs to answer the original question of why the misquoted price he finally took ownership of it & said he made a mistake.
It took 3 re-directs on my behalf mind you to get him to actually answer the question.
Good guy, good service just get it in writing or email is all.

Stay frosty

VooDoo6Actual

01-20-14, 12:46

thanks for doing that, man. I'm unclear though - is he honoring the price he gave you, then, or no?

Nope.
Just a sorry which was like pulling teeth.

QuietShootr

01-20-14, 13:32

Nope.
Just a sorry which was like pulling teeth.

<snort> No worries. Thanks again.

He did tell me to send the bad one to their service center and they would probably replace it. I'll mail it out tomorrow and see what happens.

RHINOWSO

01-21-14, 00:46

That sucks. The two in my SCARs and two spares are smooth with no issues. They should certainly replace it.

G19A3

01-21-14, 03:51

Well I gave it my best shot to help, QuietShootr.

I hope it all works out OK.

Stephen_H

01-21-14, 14:59

QuietShootr

01-21-14, 18:01

I've been staring at the picture for 5 minutes and can't see anything. Not to ask a stupid question, but it's not just carbon build-up chipping off is it (analogous to the tail of a DI bolt).

Stephen

No, there's a very large divot with a piece missing. I thought it was carbon at first too, which is why I started to scrape it.

Look at it again. I zoomed in on the piston.

http://i950.photobucket.com/albums/ad346/QS762/public/IMG_1882.jpg

justin_247

01-21-14, 18:32

No, there's a very large divot with a piece missing. I thought it was carbon at first too, which is why I started to scrape it.

Look at it again. I zoomed in on the piston.

The circled area? Looks like pitting to me.

22949

Heavy Metal

01-21-14, 18:42

I would have figured that to have been a screw or lathe turned part.

Heavy Metal

01-21-14, 18:44

No, there's a very large divot with a piece missing. I thought it was carbon at first too, which is why I started to scrape it.

Look at it again. I zoomed in on the piston.

http://i950.photobucket.com/albums/ad346/QS762/public/IMG_1882.jpg

Looks like the plating failed in that transition area. I suspect the part had bad plating. I would try and get them to replace that under warranty.

If I were FN, I would WANT that part back for QA/QC. That is a data point. They should gladly exchange it to get that back.

JusticeM4

01-21-14, 18:48

Spoke w/ my contact @ FNH USA Shanon @703.288.4507 ext 4
He says Piston in stock $31.00 & in his opinion it is a forged part.
he said he'd "never heard or seen problem before".

OP, how old is this SCAR? If its still under warranty I'd try to see if they can replace it for free.

QuietShootr

01-21-14, 19:56

I sent it back to them today. I'm sure they'll replace it. The gun is about 2 years old, it still has the 6-lug old style bolt.

JusticeM4

01-21-14, 20:12

Thats good. I think you may just got a bad piston. it happens, but as long as they replace it for you then its fine.

Every company may produce a defective product. Its what they do to take care of it that matters.

SRT-M4

01-21-14, 20:16

Looks like the plating failed in that transition area. I suspect the part had bad plating. I would try and get them to replace that under warranty.

If I were FN, I would WANT that part back for QA/QC. That is a data point. They should gladly exchange it to get that back.
Agree. The chroming flaked off and the metal began to corrode shortly after. Good find. FN needs to make this right and make sure that more do not leave the factory with any chroming issues.

Stephen_H

01-22-14, 09:24

No, there's a very large divot with a piece missing. I thought it was carbon at first too, which is why I started to scrape it.

Look at it again. I zoomed in on the piston.

Much better; I get it now. I don't know that I've ever seen a failure in hard chroming like that before. Right click, save as...