I have quite a few of the older Kato SD40, SD45, U30C, and C30-7's and I really like them for their reliability and durability. One thing that has bothered me is the way they would rumble through any of the code 55 turnouts that I have had on my last two layouts. No such problems with code 80 like on the Ntrak layout or the staging yards of my current home layout. Apparently the older releases of these models have what in the hobby are called "pizza cutter" wheels as they have a flange that is almost as deep as the rail code 55 rail is tall.
So I decided to see if I could do something about this and found that Kato USA sells packages of 6 locomotive axles with low profile wheels so I order several sets of these.
Once I got the new wheel / axle sets I wanted to make a side by side measurements of all the dimensions of both new and stock. My first impression of the new wheels is that they look more like railroad wheels. I also noticed that they also appear to be the same or similar as what are on some of my newer Kato releases. Below are two photos with the dimensions I measured on each type of wheel set.
The main difference between the two is that there is a .013 difference between the flange depth. The old wheel flanges are actually slightly larger that the height of the code 55 rail which is .055 so no wonder the wheels bumped. The wheel itself is .015 narrower than the stock wheels but since flanges on both are right on gauge I don't believe that would make any difference but it does look better.
To change the wheels the trucks needed to be removed and then opened up to expose the axles and gears. Then those are popped out and the new ones popped in, they are a perfect fit. It's a good idea to clean out the cups in the brass contact frames that the axle points go in before re-assembling the trucks.
It is an $8.00 investment in each locomotive but I feel it's worth it as they are otherwise such great runners and already have DCC decoders in them. Little by little I plan to got through the fleet with this improvement.