I don’t think the 120v starters are nearly as robust as the 12v units, but they usually do work for a long time. Points of failure that I’ve heard or witnessed: the push button switch can fail - check it with an ohm meter first. Next point is the brushes/brush holder/field connections. Mainly the brushes - they aren’t very long to start with. Maybe 5/16” of brush material at most. For how often these get used, I doubt you’ll wear a set of brushes out, but worth checking condition, size, and wear pattern on the commutator. I always scuff the commutator with 220x sandpaper if it’s any color other than bright copper. Next point of failure, and probably the biggest pain to remedy: the armature. I recently acquired an Ariens snowblower with an HM80 that did nothing at the button. Everything checked out except the armature. The resin goo they seal the armature windings with at the commutator was cracked indicating it was dropped or something slammed into it hard enough to break every single winding connection at every single commutator bar. Two wires per commutator bar and 16 bars total. If you get to this point with everything else being fine, check the resistance between every pair of commutator bars. I took a sharpie and mark them 1-16, and get out a notepad to jot down resistance values between each pair of bars. 1-2, 2-3, 3-4, etc. The exact value of each isn’t that important, but the relative consistency with all of the values is. I went through my armature and soldered every pair of broken wires back to their respective commutator bars; 1.5-1.7ohm after soldering. Once reassembled, this starter whizzes the engine over like it has no spark plug in it. Surprised the heck out of me!
My other HM80 unit sounds labored; it works as it is, but turns over slower than a 1950 Plymouth. I checked armature resistance, and found a few bar pairs in the 4-12ohm range, but that really isn’t that bad. This one had way more resin goo covering the commutator connections, but I went through and re-soldered these connections for the heck of it; 0.08-1.4ohm was the range after, so this tells me they cut some corners on the armature manufacturing. I’m reassembling the second one tomorrow, so I’ll see if the solder trick gives it more rpm. I’m selling this machine, so I don’t really care if it works or not, but having it work properly is a selling point that helps.
Sorry for the winded response. It’s Ironic this subject came up while I have been working on two starters. The only reason I’m fixing these is so I can sell one of the units; I rarely ever use the electric starter as they rope start quite well even if it’s butt cold out. I have whittled my snowblower collection from a career high of 5 down to 1, and now up to 2 again.
Of course it moves frozen water that what snow is.