I'm setting up to drill the mounting holes for the new rollers. The D3 rollers are 5 1/4 in the center section vs. 2 1/2 for the D2 rollers. This means to maintain the same clearance for the rear roller to the sprocket, I need to move the rear D3 roller forward a couple of inches. This takes the effective "wheelbase" of the track frame down from 32 inches (four rollers spaced at 10 1/2 apart) to about 30 (29 1/2). So I'm losing 2 out of 32 inches. What do folks think? I "could" keep a D2 roller on the rear to keep that last two inches. The other thing is that the centerline of the D2 roller is just behind the centerline of the pivot shaft. With the D3 roller in its new position, it's in front of the pivot shaft. I don't have a sense of whether that's critical or not. Here's some photos for comparison:

 

Thanks Jamie, I recall that now too but I thought it was mentioned on General Gear's website - couldn't find it there so I'm glad you were able to point that out. I guess I'll find out if/when I test maximum side to side articulation. Actually, I could probably do the math based on how far the spring can pivot, and the length from the spring perch back to the pivot shaft, and then the radius described by the rear roller towards the sprocket. I think I'll align the back of the 2x1s with the rear of the track frame so that if I need to redrill and position the rear roller, I'll have the option.

That's what I did, based on the General Gear information. I'm adding a 2x1 bar on the bottom flange of the track frames to space the D3 rolling surface at the same level that the D2 rollers are. My reasoning for moving the rear roller forward 2 1/2 inches was in case the location of the D2 roller center was critical to the sprocket. All the rollers have basically the same OD center section so that might just be a manufacturing consideration and the clearance might be much more than is needed. If the minimum clearance is accomplished by a D3 roller at an inch further forward, then that would suit me fine. I just don't want the sprocket to contact the center section when the frames oscillate

That would be great thanks Gee, much appreciated! I'm ready to start drilling any time now : ) I put the hard word on the machinist to get the pivot shaft done but he holds all the cards. I have several days of welding and messing around (at my slooow rate) before I need it anyway. New bushings from Grainger are on their way. Bought the same ones Toby put in his 5J so the pivoting should be just about perfect when done.

Thanks Gary, are those the ones on facebook? I can't see them unfortunately as I'm not on that platform. Do they have a contact # to ask about them and are they after 5U13237?