Century piston hole out of whack

[G3isMe]

I have a new Century "inch" receiver that has the piston hole out of alignment (off center). To make matters even worse, the hole does not appear to be "square" in relation to the other holes, i.e., it is drilled at an angle relative to the barrel hole. It is so out of whack that when I checked it before I barreled the receiver by screwing in the gas tube nut and tube, the piston won't slide through freely. When the piston does make it through, it is at such an angle that the end of the piston dang near hits the inside of the receiver. The last one I had like this I "fixed" by reaming the hole out with a Dremel, but it ended up looking like crap. Any suggestions on how to ream out the hole so it isn't to oversize, yet will still allow the piston to operate correctly? Also, if the hole is oversized (which will be the end result of fixing this problem), am I correct in assuming this increases the chances of bending the piston during cycling?

[Radio]

Since there's no gas seal in this area, your hole can be slightly oversize. The thought comes to mind, however, that I am totally clueless whether this could cause potential reliability problems with a piston flopping/binding due to the extra clearance. Barrel timing will also require extra attention, since any check of piston freedom of movement will obviously be less informative.

Assuming you are going to employ "backyard" tools, I would attempt correction with:
1) VERY CAUTIOUS use of a dremel;
2) a drill press with a looong drill bit and VERY CAREFUL, triple-checked setup;
3) a phone call to Century asking for a replacement receiver. (Ah, I like this one.)

If you wanted to be creative, I could imaging sacrificing your import piston for a homemade tool: slotting the carrier end of the piston to receive a roll of coarse sandpaper, and drilling/tapping then screwing on some kind of extension (concentric!) to the gas end of the piston. Chuck the thing into a drill, slop lots of grease around the piston head, slide the whole enchilada down your gas block (without a long tube, okay to leave a short tube in place) and line up/open up your receiver's piston hole that way. (This, of course, assumes you've already barreled the receiver in question, and that the piston end already fits at least somewhat into the receiver's piston hole.) A glorious path to true WECSOG brotherhood.

This has hurt my head. Going to bed.

--Radio

[Stoney]

Had the same thing on mine. The gas tube nut is what guides the piston, so opening up the hole above the chamber is no big deal. If its the gas tube nut hole that's off, get Century to replace it.

[G3isMe]

Originally posted by Radio
......If you wanted to be creative, I could imaging sacrificing your import piston for a homemade tool: slotting the carrier end of the piston to receive a roll of coarse sandpaper, and drilling/tapping then screwing on some kind of extension (concentric!) to the gas end of the piston. Chuck the thing into a drill, slop lots of grease around the piston head, slide the whole enchilada down your gas block (without a long tube, okay to leave a short tube in place) and line up/open up your receiver's piston hole that way. (This, of course, assumes you've already barreled the receiver in question, and that the piston end already fits at least somewhat into the receiver's piston hole.) A glorious path to true WECSOG brotherhood.

This has hurt my head. Going to bed.

--Radio

I have already barreled them as I didn't want to send them back, as I have had them laying around collecting dust for several months and I know that it is a crap shoot if the new ones would be any better. I actually have two barreled with the same symptoms, one worse than the other. The threaded hole (gas nut hole) appears in line and square relative to the other landmarks. Out of the 5 Centurys that I have barreled, counting these 2, 3 of them have had this problem. I guess I am a glutton for punishment, but I couldn't resist the price when they went on sale for $125 (now I think I know why they were so cheap), Oh well I expected to tinker with them.

Back to the problem. It is the smaller hole closest to the carrier that is off. I too usually use the movement of the piston through the receiver, etc., as a check for barrel timing, but obviously that option flew out the window. For these two I used witness marks, levels, and the two rod method. I like the idea of using an old piston for a reaming rod. In order for this to work I think one would have to turn the diameter of the piston down a small amount in order to fit the the rod with the sand paper in it through the receiver hole. Were you thinking of using a flap of sand paper, or small drum like one made for a Dremel. The drum option may be the way as I could drill and tap a piston to accept a small drum attachment, Hmmmm, I am going to try this. :biggrin: :] If all else fail I can always fire up the Dremel with a grinding stone. WECSOG 101 credits here I come!

[W.E.G.]

chainsaw file

[ce]

Yeah, I had one that was off about the same, and a chainsaw file is the way to go. Stick it in with the tang forward and use it as a draw file. Check often, and finish it up.

[G3isMe]

Originally posted by gary.jeter
chainsaw file
Damn, just when I thought I had an excuse to make a new tool attachment you come and tell me an easier and cheaper way to do the job. :wink: No WECSOG credits for me today. I'm off to the hardware store for a chainsaw file.

[W.E.G.]

Them chainsaw files is real brittle. They'll snap in two if you lean on it too hard. Leaves a real sharp break that'll take a chunk outta the side of your hand if you aren't paying attention. AMHIK. :uhoh: