Correct torque is key for install.
There needs to be absolutely no play between crank and BB at install.
Sounds simple right?
It can get weird pretty quick.
Rock solid when in the bike stand, but after a bit of pedaling, play develops and the crank arm backs off the spindle.
Some of the newer GXP are super reliable and will give no grief for their entire service life.
Others will do exactly what you describe.
If you detect play at install, remove the crank arm, grease the spindle again, and tighten it back down. Repeat until play stops. You should be able to put a good torque on it before overloading the bearings in the BB.
If you detect no play at install, but loosening begins when riding(which I think is what you are describing), the same approach applies. Remove crank arm, grease spindle, install arm and torque it down.
SRAM has the torque specs on their site.
Unfortunately, you can reach the specified torque on a "dry" spindle before the crankset is properly tightened down.
I'll bet that is the problem, even though it felt tight on install, it wasn't really tight enough.
GXPs that give continued problems have always been fixed for me by removing the crank arm, greasing the spindle, tightening it back down aggressively, and then checking tightness again before riding. For the next few rides, check tightness before and during riding, and tighten if necessary. You should only have to do this a few times if you didn't not get the cranks tight enough on the initial install.

 

Hey thanks for the input, yeah it's definitely not loose anywhere @ install, steep mashing brings it on. The play starts with the ticking and then creaks. Originally I was blaming the pedals because of my experience with a couple solid truvativ's.. I installed the x7 to spec from new and basically what I've tried so far after it loosened the first two times- clean and torque to spec with the stock grease (this SRAM had 3x more grease on the threads than the older truvativ's did), 3rd x tried park grease and that was last week so now that its loose again im wondering if it would hold dry.. anti-seize and bump the torque way up.. never tried loctite..or maybe the fixing bolt is just not mounted flush in the nds arm

 

Since you've had that arm on and off several times, it should be seating fully on the spindle by now.
I'd try more torque and see if it stops loosening.
I have 3 newer GXPs set ups here have been tightened down enthusiastically with no sign so far of too much preload on the bearings.
If you're needing to tighten to the point of excessive load on the bearings that would be weird.
I've seen a few GXP arms loosen to the point of falling off/almost falling off on the trail, and the fix has always been getting them tighter at install.
That bolt should not be backing out, so I hope you find the fix before going the Loctite route.
Have you pulled the bolt to inspect for wear or damage?

 

Thanks

There is no such thing as a side load on bearings with the GXP cranks, hence you cannot overload them. Just tighten the heck out of the bolt and make sure the splines are well lubed.

Had to tighten a chainring bolt, but after 20 hammered miles the arm is still holding solid so I'd consider it solved.. tried to take off the extraction piece and think it's frozen with loctite, oh well, deal with it later. Anyone reads this w/ the same problem slam that sob (almost guerrilla tight)

 

Haven't let it loosen that much yet.. It's not detectable until after the ticking and then creaking starts. At that point I can hold the chain stay and the crank arm aligned and push/pull to feel the small amount of play.

I'll have to take a look does that outer extraction plate come off, how did you get the bolt out to check it?

 

10mm allen for the outer extraction cap.
I've seen some GXP cranks come new with no loctite on the outer cap and others have green threadlocker installed.

 

There is no such thing as a side load on bearings with the GXP cranks, hence you cannot overload them. Just tighten the heck out of the bolt and make sure the splines are well lubed.

 

first of, Like StiHacka said, there is not pre-load on GXP. the system works by trapping the inner race of the non drive side bearing between the crank arm and a lip in the drive spindle. If you over torque the only thing you'll damage is the bolt will distort or strip (it will, I've done it) If you torque to spec, it should never come apart until you want it to.

issue that may have caused it to come loose...

• To many spacers to frame. Crank arm doesn't get enough bite on the spindle. The Alum of the crank arm wears/flexes/distorts and as you pedal it moves back and forth which will cause the bolt to work loose. I've seen this when someone gets a chain guide that mounts to the BB and doesn't remove a spacer when installing and also when they think it's a 68 BB shell and it's really closer to a 73. - Fix, you need a new crank arm AND BOLT at this point, and remove a spacer from the BB cups-frame.
  
• Bolt was OVER TIGHTENED and the threads are pulled out of shape (basically just before they strip out) and they no longer hold tight to the threads in the spindle. The threads have been weakened and stress allows them to flex a bit which in turn lets the bolt loosen. - Fix, new bolt (If you regularly pull the cranks, replace the bolt every third service, it's a tad over kill but cheap insurance)
  
• Bolt wasn't tightened enough or threads/interface was dirty at install.. - fix, new bolt, clean everything re-install.

Honestly, Locktite doesn't work. The best thing at this point is to purchase a new bolt (like 10 bucks if you search around, lots of bling colors from after market's too ) clean/de grease the threads out super well on the spindle and splines on both the crank arm and and spindle. Use PLUMBERS TAPE on the bolt(s) no grease on the threads but lightly grease the splines on the spindle. You only want 2 wraps of tape on the threads. It's easier to do if you wrap the plumbers tape on the bolt before installing into the crank arm then install the outer/removal nut.

One more thing, and sorry to inform you, but once you get that click, it's more than likely the splines in the crank arm are distorted and you'll always have issues. you more than likely need a new crank arm. But you can try just getting a new bolt, you'll know quickly if the crank arm is bad.

GXP systems are better designed... once installed. But during install they can be very finicky to cleanliness and if there is even a little spec of dirt in the wrong place it can end up badly.