Exposed needle-bearings on inside of axle boxes

[rkcarguy]

I generally do not like having a needle bearing running on a non-hardened shaft surface, but, will share a story lol.
I have a 4-cycle racing go kart, and the centrifugal clutch I used for awhile had a needle bearing in it's hub that runs on the PTO side of the crankshaft which is not only not very hardened steel but it also has a keyway cut in it! I called the clutch company wondering if there was supposed to be a sleeve and they said no and it will work fine
So I carefully deburred the edges of the keyway pocket, cleaned everything, lubed it up with a little hi temp silicone grease and slipped the clutch and hub onto the crankshaft. Our track is a 19 turn asphalt track, and some of the corners are tight. To trim a few extra 10th's of a second I run a higher lockup RPM on the clutch and it helps launch you out of these turns but it also means this bearing works harder as whenever the clutch isn't locked up this bearing is spinning at anywhere from idle speed to 2700rpm. We warm up in pre-grid and sit there for several minutes while the previous race clears the track, the chain puts a side load on this bearing, the whole clutch gets hot, and we race in the rain with a lot of tire rubber coming off that gets into everything. I can't have too much grease in there because it can fling out and contaminate the clutch. It all ads up to several ways this bearing can fail. Well a whole season goes by and I'm heading into the last race in essentially a tie for 1st place points with 2 other racers. I didn't want this bearing to come apart (Murphy's law of course is always waiting especially if one is winning) so I ordered new bearings and fiber washers (seals wouldn't survive the temperatures) ahead of time and took it apart to replace them. There was no need, the bearing and even the grease I used still looked perfectly new.

[skid-roe]

Just an observation.
I am rebuilding a 30+year old coal burning Little Engines Baldwin Mogul 2-6-0.
It was built per the Little Engines plans with 13/16" needle bearings running on regular (non hardened) steel axles. The bearings had been greased regularly to keep the dirt out.
Upon teardown of the engine, the some of the axles had some SLIGHT pitting, which cleaned up with 3M Scotch-Brite cleaning pads.
It looks like that the the engine can go another 30+ years without worrying about the axle bearings, just keep the bearings greased !

[10 Wheeler Rob]

One the Allen locos the axle box has flanges only on one side and they are allowed to float back and forth in the frame by about 1/16". So I think they probably tend to stay up against the washers held by snap rings. They also have grease passages thru the axles that feeds the bearing in the center. So when you grease it tends to flush the dirt out of the bearing.