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Bolt Return Spring (Part No. 76) Broke


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#1 ky2970

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Posted 17 March 2013 - 02:07 AM

So this happened today after two games. It was fine during the game but it broke when I tried to just normally lock the bolt back manually to clear the LM4.
Posted Image

Good thing I have my NPAS en route... But has anyone seen or had this problem? Or what could've caused it? The reason the spring is kinda mashed is because I had to force the bolt into the carrier to disassemble it. But as you can see, the spring separated into 3 pieces...

Also note that I have not modified this bolt in anyway. I've never taken it apart or anything. Running dry propane but I keep up with maintenance.

Edited by ky2970, 17 March 2013 - 02:09 AM.


#2 Chuck S

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Posted 17 March 2013 - 03:44 AM

The the bolt stick forward in the chamber when retracing the bolt carrier?  I'm thinking lack of lubrication but that's a wild guess.

I can see a spring breaking at one point if stretched too far, but not in three places.

I'd think the spring is an available part if you call the Pro Shop.

-- Chuck

#3 thatguyx

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Posted 17 March 2013 - 08:47 AM

i bought my friend's used broken lm4c and this was the exact problem.  Bought the return spring assembly for about 10+shipping and threw it in.  I think he had less than 3000 rounds on his lm4c.  I think he may have over lubed (as he does with everything).  However, the replacement broke within 5000 rounds, and i ran it lightly lubed.  I think the problem is that it breaks at the point where it attaches to the pins.  Probably just a natural weak point.  The spring breaking in 3 or multiple parts is just from the constant slamming of the piston into spring itself.  

In terms of preventing this problem... there isn't much i can think of besides regular lubing and maybe angling some parts of the bolt carrier shown by dobey a while back.  

The NPAS piston return spring is definitely beefier looking and shouldn't be a problem.  I may have to pick one up next paycheck.

#4 akiraspeedstar

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Posted 17 March 2013 - 09:03 AM

I also have an NPAS on the way, even though I have a complete spare BCG on the side.

#5 ky2970

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Posted 17 March 2013 - 08:27 PM

I did dobey's tips on the bolt carrier and mine was moderately lubed with 30wt silicon oil. And like was said, I'm pretty sure the second break was from me trying to get the piston back in.

#6 okay47

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Posted 17 April 2013 - 09:10 PM

A little late, but I just encountered this problem today and am searching for the part no. 76.  I contacted KWA and they're all out of stock, my local stores are also out of stock as well.  I've checked Home Depot and alas they have a set of springs which are the correct length but just a size too large to fit into the nozzle tube.

I think I've found a suitable spring size through a specialty hardware retailer:
www.tacomascrew.com

lol yes I know it sounds like a porn website but trust me it's not (I wish it was).  I'll let you guys know when I get it, if anyone's interested.

#7 thatguyx

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Posted 18 April 2013 - 05:51 AM

Called the pro shop yesterday. They're expecting a shipment in maybe two weeks. But definitely interested in finding just a replacement spring. Seems silly having to buy a whole assembly for $10 when you only need a $2 spring.

#8 Rockhound117

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Posted 18 April 2013 - 08:28 AM

I suspect McMastercar would carry a suitable spring. The trick is finding it.

#9 netpoc

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Posted 18 April 2013 - 06:40 PM

Try your local hobby shop. I found a 2 pack for $4!

#10 thatguyx

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Posted 18 April 2013 - 08:05 PM

View Postnetpoc, on 18 April 2013 - 06:40 PM, said:

Try your local hobby shop. I found a 2 pack for $4!

Got any details, ie brand, size/dimensions, strength?

#11 netpoc

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Posted 19 April 2013 - 04:38 PM

These springs were from a RC car. I can't remember the specifics, but it was the only one of that size.

Posted Image

Posted Image

The size is 1-1/4" long x 1/8" thick. The tension is a little bit stronger than stock resulting in a slightly quicker rps (14.1 stock to 14.7 with this spring, for those of you who care. None the less, it works and it's in stock and $2.

#12 okay47

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Posted 19 April 2013 - 05:34 PM

Nice find, thanks for the info.  I got about the same specs as yours (2.5" length and 9/64" OD, practically 1/8").

Link:
http://www.tacomascr...t.A/id.13401/.f

By the way netpoc, did you knock out the pin in the rear silver piece to attach the spring or were you able to hook it up by opening up the loop in the spring?  Thanks

Edited by okay47, 19 April 2013 - 05:40 PM.


#13 netpoc

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Posted 19 April 2013 - 05:41 PM

I think you'll find that is way too long. The max length that spring can be is 1-7/16" or it will not allow the bolt to fully return. Oh and by the way you had better have a good 1/16" punch.

#14 netpoc

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Posted 19 April 2013 - 05:46 PM

I punched the pin out just enough to allow the old one to escape and sneak the new one in there. Don't completely remove it or its a pain to get started again.

#15 okay47

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Posted 19 April 2013 - 05:51 PM

Yeah thanks for the advice.  I initially tried to punch it out but it was taking quite a bit of effort and since I didn't have a replacement I just took the old spring and reshaped a loop for it.

#16 netpoc

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Posted 19 April 2013 - 07:04 PM

I found it helpful to have a 3rd hand... I held the punch and the part and put the roll pin over a phillips head screw in my workbench, while someone else gave it a good whack... Just enough for the pin to come out enough to take the old spring out and slip the new one in.

#17 okay47

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Posted 26 April 2013 - 12:08 AM

Hey netpoc,
Just got the springs in this week.  You were right, 2.5" was longer than what I wanted, but I can always cut those springs down and recoil them if I ever need to.
I placed another order with tacoma and got the 9/64" OD and 1-1.5" spring and they were just about right (maybe 1mm short).  I didn't want to break another punch (I broke my 1/16th last time) so I was able to slightly open up the hook on one end and wiggle it onto the silver piece.  Everything seems to be in order now but I'll be curious to see how it holds up since I had to open up the hook on one end.  Thanks for the advice

#18 netpoc

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Posted 26 April 2013 - 05:58 AM

No problem, and good idea to cut it. For the cut end you could just take about 2 coils and bend them 90 degrees making that connection point.

#19 -wigs-

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Posted 29 April 2013 - 04:52 PM

Wait you've never taken the bolt apart?
So how did you get the harbor freight oring on the nozzle? If you just pulled it out till you could get to the oring fully you overly stretched it out.
This just happened to me literaly a few hrs ago, a week after swapping to the danco #10 on the nozzle and 20k rounds into it. I think some #10s are too fat causing the nozzle to pull out but not return. I just clipped the 1/8inch of messed up spring off, folded TWO coils over instead of one and reassembled. The two coils around the pins instead of one should help, only qualm is the nozzle has a "stronger" return spring now so it only pulls out about an 1/8 of an inch when the bolt cycles and snaps right back. Shot a few mins ago and there is no loss in range or fps do all seems good.

#20 okay47

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Posted 29 April 2013 - 06:09 PM

View Post-wigs-, on 29 April 2013 - 04:52 PM, said:

Wait you've never taken the bolt apart?
So how did you get the harbor freight oring on the nozzle? If you just pulled it out till you could get to the oring fully you overly stretched it out.
This just happened to me literaly a few hrs ago, a week after swapping to the danco #10 on the nozzle and 20k rounds into it. I think some #10s are too fat causing the nozzle to pull out but not return. I just clipped the 1/8inch of messed up spring off, folded TWO coils over instead of one and reassembled. The two coils around the pins instead of one should help, only qualm is the nozzle has a "stronger" return spring now so it only pulls out about an 1/8 of an inch when the bolt cycles and snaps right back. Shot a few mins ago and there is no loss in range or fps do all seems good.

Hmm, not sure what you're asking.  But yeah, that's originally what I did with the broken spring until I got my order from Tacoma and replaced it.

EDIT: nevermind, looks like you're addressing OP.  Sorry bout that

Edited by okay47, 29 April 2013 - 06:11 PM.





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