Ive been loving my new D2 5U orchard model and have been putting it to good use clearing a fire break around our property. But every time I take her out I come back to the barn with an issue. This time, I was out discing and felt/heard something that didnt sound right with the left track. I stopped and inspected, the left rear sprocket nut was loose and noise I was hearing was the track rubbing against the sprocket as well as the front idler. Im guessing the sprocket slide out due to the nut being loose and started rubbing against the track. 

I was able to limb back to the barn and here's what I found. The nut, locking retainer and the face of the sprocket all have a lot of wear, Im guessing due to it being loose. I know I need to press the sprocket back on but what should I do with the face of the sprocket and nut, do you think with the parts looking as they do, would I be ok to put it all back together after the sprocket is pressed on? Or should I try and do some repair machine work to get nut and or face of the sprocket flat again? Im only using this D2 for discing and only plan on working it once or twice a year, besides taking it out for a joy ride here or there. Thanks!

Hi, btsclan.
It's not quite as simple as just pressing the sprocket back on. If it has been running like that for a while, there may be too much wear in the splines for that to work. The nut was only ever designed to stop the sprocket falling right off on the ground. It is the press fit that is designed to hold it on. Excessive wear in the splines will make that a non-event so you need to examine the splines closely before pressing the sprocket back on - which may well mean breaking the track. On the (slightly) plus side, at least you don't need to remove the track frames to get the sprocket off to examine those splines.

OR, you could just try pressing the sprocket back on and hope for the best. Depends on whether you want a working tractor or 'toy'.

Just from your photos - and with my limited mechanical knowledge and judgement - I would say that the nut and the axle thread will be O.K.. It might be a good idea to 'acquire' a new lock washer.

Just my 0.02.

depending how bad it is worn you may be able to repair the splines use loctite quick metal or devcon metal epoxy

I thought you checked this back when you were asking why there's an oil leak. As you see, here is where the oil is coming from.
Hopefully the tractor hasn't too many hours running and the tapered splines are not trashed because the sprocket wasn't pressed on correctly. You have said that the previous owner put new steering clutches in not long ago and it appears it wasn't put back together properly.
I would get someone with the proper hydraulic press and try pushing it to the recommended 15-17ton, clean off as much oil you can with some Break Kleen put some sealer under the washer and nut. Tighten it up and give it a try. If it gets loose again, splines may be junk. Remove the track and remove the sprocket. If bad, you may get away with what Trainkid said.

Thanks, @side-seat, I have to admit I was planning on sorting out the axle nut leak but ended up slipping my mind to check

Looking at the nut and wear on the sprocket Im guessing it had been loose for some time. Im thinking that the previous owner didnt install the sprocket correctly when they rebuild the steering clutches. It also lived most of its life on a flat farm discing between orchard trees. My property has some steep hills so I was probably working the tractor harder than it has worked in a long while which could have caused the sprocket to slide out. 

I want to do it right and keep this tractor running for a long time. How much of a PITA is it to remove the track? My biggest reservation on tearing into it is finding the right tools and presses to get the job done. Where would one find a press and tools to remove the track and pull/push the sprocket back on?

I recommend watching Squatch253 videos on YouTube he shows everything on doing this job. I just did steering clutches on my d2 I didn’t separate the tracks I just loosed them up to where you can pull them off it’s not hard a little time consuming.

Interesting, thats good to know you can remove the sprocket without breaking the track apart. Im going to try and find a hydraulic ram and press the sprocket back on and see how it holds, if it comes loose again then I'll pull the sprocket and hope the splines on the shaft arent damaged.

There is a specification for how far the sprocket should be pressed on . Squatch's video should have it. If the shaft is worn you will be in for a more complicated repair. Parts tractor time.

Take a good look to the spline, if ok press them on with 15 to 20 ton.
If the spline is facing trough the sprocket you may have to adjust the nut, turn the inside out a bit on the lath.

And dont forget press the other side also! one failing spline is enough!