Looking at the Challenger172 manuals... the pictures are really ratty... Here is the roll picture from the Challenger manual which shows the 2 grooves, one groove is notched, the other is smooth. You just remove the set screw and flip the roll on the shaft to use the other groove.
- Challenger_roll.jpg (5.22 KiB) Viewed 13217 times
It looks like the Challenger172 had 2 different drive rolls, it was originally part 165603, but was later changed to part 090423. Perhaps the earlier version only had one groove? The later is the same drive roll as used in the Miller 130XP/150/185, so it should be pretty available at parts stores. EDIT: Found a clearer manual and a third party store with the 165603 part and it does appear to show a single groove. The 090423 replacement also appears to be a single groove? I could have sworn the all the Challengers and the 130XP/150 used a dual groove roller, but apparently not? Ouch on the price...
I made my replacement roll out of plain mild steel with a V groove in it. Hardened would probably be better, but it probably doesn't see enough use to warrant. The groove is a simple sharp V, it doesn't need to be deep, just enough to hold ~1/4-1/2 of the wire diameter to keep the wire in place (and setting the groove in line with the feed helps immensely). The traction is really done by the friction between the upper and drive rollers. It was extremely easy to make on the lathe in a few minutes, center hole with a slightly snug hole to the shaft, outside diameter a bit larger than the stock (this was a bit of a guess), part off and drill/tap a hole for a set screw. I made a few different grooves of various depths in my replacement, but ended up using the shallowest as it seemed to give the best grip.
The Challenger172 originally used the 10A or M-10 MIG gun (the Challenger used the M15). The replacement for that is the M-100 MIG gun or M-150 depending on serial number. According to the 2021 parts guide, the M-100 is now apparently replaced with the MDX-100. The liner kit for the M-10 MIG gun is 194010 for .023/.025 or 194011 for .030-.035, which are both readily available. For the old 10A the part number was 129178 for .023-.030 and 129179 for .030-.035, which don't seem to be available any longer
See the official Miller Parts Guide for the latest numbers. Miller tends to be extremely good with making all their manuals and replacement part numbers available. The Challenger172 shares a lot of parts in common with the later Millermatic models, so other than the 10A MIG gun, most replacement parts can be found:
https://www.millerwelds.com/-/media/mil ... .pdf?la=en
If your MIG wire is splitting it is definitely bad. The wire shouldn't be able to be crushed in the rollers. I would start by blowing out the MIG gun liner, put in a new good roll, check that there is a gap between the tension arm and drive base so the spring has some action, and make sure the polarity is set right (DCEN for flux core, DCEP for gas). When you feed the new roll, I would first lay the MIG gun out flat and feed by hand, it should slip thru fairly easily with only a small constant drag up to the tip (which will be harder to initially push thru, then easy again). Pull it back out and feed in with the drive. If there is skipping or hard places to push in the gun it may be a bad liner.