Helwp! w/ YFZ Bearing Carrier & Axle Nut issue

[Sazjun]

Having a problem with my son's YFZ.
Started a couple weeks ago, he kept saying, Dad it's making a noise. I test rode and could not hear it.
Then last week he noticed the Axle nut was a few threads loose.
So I tightened it down, but then it wouldn't roll easy, so we loosened it back up a half turn and set the allen set screws in.
Rode it the next weekend with no problems but when we got home, the axle nut was a few threads loose again.
So I took it by the shop on Saturday and had the Yamaha mechanic look at it and tighten it down. He mentioned that we might be having a bearing problem.
Took it to Speedworld MX on Saturday night.
Same scenario, my son kept saying it was making a noise, but I couldn't hear it. Then an hour later he was saying that it felt 'loose and jiggly' when jumping. So I took it for a spin on the track.
It felt a little loose to me, I would have guessed swing arm bearings. Then about half way around - the chain shot off and jammed up between the front drive sprocket and the chain guide roller. The chain locked up tight around the axle and we were unable to get it loose, we towed it back to the trailer and took it home.
Pulled the shock and swing arm off of it last night (had to to get the chain unjammed) and gave it a good look over, The swing arm and shock linkage bearings all seem good, dirty, but no play and easy to move.
Then I got to looking at the axle and bearing carrier.
The rear sprocket has managed to slide right enough to gouge out the port side of the bearing carrier and has ground itself down about 1/8" into the carrier. The axle nut is loose about 3 threads. When you spin the axle it feels smooth and easy, but if you hold the axle and swing the swing arm, it grinds and grabs and doesn't sound good at all.
I am guessing that I am in for new bearings, seals and bearing carrier, but I want to make sure that is all the problem is so I don't get it back together just to tear up another bearing carrier.
The axle will play back and forth about 3/16" of an inch relative to the carrier, would that have been enough to throw the chain?
Any feedback from somebody that has experienced this problem would be appreciated. Thanks.

[Bowtie]

What year is it? 04/05 or an 06+? If the chain was adjusted to tight or to loose, 3/16's is all it would take to toss the chain.

[Sazjun]

06 - stock rear setup.
Had the axle replaced by dealer at 6 months, had the weak spline issue.
Loves to roost the berms, I'm sure that places extra stress on it.

[Bowtie]

Since it ground into the the side of the carrier, I would suggest that you replace it with a Lonestar carrier and if you can swing it, grab and axle and another lock nut. Double check the brake pads as well for any wear that might have happened there as well.

[Sazjun]

Does the Lonestar carrier fit the stock swinger?
Is it known to be of better quality?

Does it sound like my problem is centered around the bearings/carrier?
Or is there something else I should be looking at too?

[Bowtie]

Double check with Lonestar but I believe it does. And yes they make two different carriers, one cast and one billet, I personally run the billet with a +2 Lonestar arm on my 05 YFZ. And from what it sounds like is the bearings went bad and they were allowing the axle to get some movement as well as nut loosening up a bit probably due to someone trying to loosen the nut before removing the set screws, and so that is why the nut kept backing off and giving you the play.

[06YFZ45racer]

I had almost the EXACT same thing happen to me. My problem started with chain coming off and binding up against counter shaft sprocket and case saver! Thank goodness for that!

I bought a Slide N Glide kit for chain and new sprocket. Next weekend raced at ACP for ITP rnd #2. Got home and kids were climbing on quad. I noticed that the whole quad was moving up and down in the rear. I thought i had broken the frame/subframe, but it is gussetted. I kept looking and saw that the left side axle carrier bearing was toast and the axle was moving freely up and down in the carrier. I had to replace carrier with a new Lonestar part (which comes with new bearings and seals) and also replaced sprocket hub due to damage.

the only thing i can think that caused this was the week before when the chain came off and tightened up against the axle it stressed the left side carrier bearing and i didnt notice a problem then. I had just replaced all bearings and seals when i had the swingarm off for powder coat. The new bearing had approx 5-6 rides on them before the chain came off. I also nostice that the axle nut backs itself off a few threads during hard race/riding conditions, and I am still running stock axle nut w/ set screws.

[Sazjun]

Thanks for the feedback guys.
Sounds like I'm looking to replace the bearing carrier with the Lonestar version.
Just another $200 - I keep saying that everytime we go out it seems.