The track frame alignment with the sprocket is pretty critical. With the track separated and laid out, you use a stringline along the top of the sprocket, carrier rollers and idler to set the alignment of all three items.
The track frame position can be altered by inserting or removing shims from the track frame guide plate that is situated behind the big cast cover with 6 bolts in it, on the outer hub of the sprocket shaft.
Toe-in and toe-out is also a critical measurement for track frames. You measure centre-to-centre between sprockets and idlers and compare the variation in measurements. It should not be any more than about 1-2" - 3/4" difference.
Excessive toe-in or toe-out is caused by bent track frames, or wear in the outer hub bronze bearing, or wear/breakage in the bearing shells under the diagonal brace caps.
Another factor is whether the diagonal brace is bent or not. A diagonal brace with a bend in it can make the entire track frame tilt in, or tilt out, at the top (not vertical).
The diagonal brace looks unbreakable, but they're not as strong as they look, and they bend more easily than you might expect.
In fact, when the D6C was released in 1963, the diagonal brace was so weak, and bent so often, that Cat had to produce a factory upgrade that involved welding plates top and bottom to the diagonal braces, to strengthen them.
This was a free factory upgrade, and my first D6C, purchased in Dec 1966, had this upgrade applied to my tractor by the local Cat dealer, at no cost to me.
So you will find a lot of early D6C's wearing plated diagonal braces. My second D6C, bought new in April 1968, had strengthened diagonal braces, and did not need the factory upgrade plating.
