Unusual wear on chain tension adjustment bolt!

I was adjusting my chain tension today and noticed that the chain side (left) adjustment bolt was a bit hard to turn. I pulled it out to put some more anti-seize on it an squirt some PB blaster in the hole, when I noticed that the threads are worn down and rounded off.

This is only happening on the chain side. The brake side is in perfect condition.

Chain tension has been carefully monitored and the adjustment bolts have always been tight.

Any idea of what might be causing this?

Worn bolt on left, good bolt on right:


It looks like one of the spare bolts that I have had in my tool kit for years and is just worn down by the constant rubbing against other loose bolts while trail riding.

Yup, Both my Huskys 07 510 SMR and my 11 TE 250 have the same issue??? I removed the chain guard
on the 510 ( never plugged the holes) , I thought maybe some crud got in there ???. Then I got my new
250 and swapped the rear sprockets 40 to 50 that came with the bike. and found the same issue (left side). Not sure why now, I never road the 250 hard during the break-in. Always Torqued axles to spec.

Something got in a bind during an adjustment or the axle was not tightened securely enough while riding. Once the subtle damage was done to the thread insert, it continued to damage the threads on the bolt when you removed it. Be sure to run a tap in the hole or you will damage another bolt.

The drive side is taking more of the load also, probably why the right side is OK. BTW, I had my bolts out a while back and no issues.

Same thing on my bike, I was swapping CSSs alot in the beginning, adjusting the chain alot, it was driving me crazy, so I ran a tap into the hole, and ran a die on the bolt, put a tiny dab of heavy grease on it, and it has been OK since then. I always thought it was an isolated thing to me, I never dreamed that it was happening to others.

Exact same drill to above i did, tap and die and never seize paste.

You guys are just talking about cleaning up the treads, not installing a Helicoil are you?

Same here on my 09 SM. Only on the LHS. Ran a tap through the s/arm hole and replaced with SS bolts. I wondered if there was some weld or part of the s/arm fouling the bolt inside the s/arm. Also you need to tap the hole to the depth of the tap to clear it good. Then some copaslip grease.

On my bike it was some weld (bead) that was inside the swingarm. Even when I cleaned it up with a tap, a small piece of weld got caught in the threads and ruined a new adjusting bolt I was installing.

Yes just run tap and die no helicoil.