Atlas/Craftsman 12 spindle back gear (10-242) bushing wear

[Bill1958]

Hey guys...could use some input/advice on something I am thinking about doing. I've been trying to come up with a good reason or two as to why I shouldn't do this.
So far...no luck. So any input from you guys would help! I'm sure someone has probably tried this in the past but I couldn't find any info on it so far.

I'm rebuilding the spindle assembly on my A/C 12...new bearings and 3 new bushings. When disassembling I found that the bushing in the spindle back gear (10-242) had excessive wear...that I could wiggle it while it was still on the shaft. The 2 bushings in the pulley (10-79) shown wear but were not a loose fit.

The pulley has the access screw for oiling the 2 bushings...but the bushing for the spindle back gear can only receive whatever oil manages to travel across the spindle from the left roller bearing and from the right from the pulley bushings. Since there was excessive wear on back gear bushing there probably wasn't much oil getting to it.

What I wanted to do was to drill an access hole thru the gear and bushing...use a bottom tap and plug it with a screw like on the pulley.
The small amount of material removed from the gear I'm thinking wouldn't hurt it's integrity and with the screw seated below the bottom land of the gear it wouldn't interfere with the gear mesh. Using the bottom tap I should be able to snug the screw down good enough where it wouldn't walk out. Probably something I would inspect each day before use.

Well...that's my thinking about it. What am I missing here....why would this be a bad idea?
Thanks guys!

Bill

 

[markba633csi]

Seems like a reasonable upgrade- remember though you wouldn't snug the screw down far enough to touch the spindle
since the gear (and pulley) rotate(s) on the spindle in backgear mode
In fact, it would be a better idea not to use a bottoming tap and cut the threads not quite all the way thru such that the screw begins to bind just as the top of the screw clears the lowest point of the gear teeth but before the screw touches the spindle surface
-Mark

 

[mattthemuppet2]

I'm a little confused - the back gear should be secured to the spindle at all times, it's how drive is applied to the spindle in both direct drive and back gear drive. Only the spindle pulley rotates around the spindle in back gear drive (and is locked to the back gear by a pin in direct drive). If there is a bushing in the back gear it can only be there for fitting the back gear to the spindle, not to act as a bearing surface because the back gear doesn't rotate around the spindle. No idea why the one in yours was worn, perhaps because the back gear had been run loose by a previous owner? Either way, as long as you're able to secure the back gear to the spindle at the correct spacing from the spindle pulley then you should be good.

 

[Bill1958]

Seems like a reasonable upgrade- remember though you wouldn't snug the screw down far enough to touch the spindle
since the gear (and pulley) rotate(s) on the spindle in backgear mode
In fact, it would be a better idea not to use a bottoming tap and cut the threads not quite all the way thru such that the screw begins to bind just as the top of the screw clears the lowest point of the gear teeth but before the screw touches the spindle surface
-Mark

Hi Mark....thanks for your input!
Yes...I don't want to get anywhere near the spindle shaft...that's for sure. My thought on using a bottoming tap (or a blind hole tap...same thing?) was to just go deep enough so the screw wouldn't stick up into the gear mesh. I would run out of thread before getting even to the bushing.
Was going to Loctite all the new bushings with Loctite 680. I read that for removal...use a hot air gun at 400 degrees would break the seal.
Thanks again for your help Mark!
Bill

 

[markba633csi]

To clarify: the large Bull Gear is keyed to the spindle- we are referring to the spindle take off drive gear which is coupled to the pulley with dogs/lugs
The factory calls it a back gear which is kind of a misnomer
Instead of Loctite you could use something like Rectorseal #5 plumbing compound which on exposure to air thickens to a sticky clay-like paste
which would hold the screw fast but permit easy removal

 

[Bill1958]

I'm a little confused - the back gear should be secured to the spindle at all times, it's how drive is applied to the spindle in both direct drive and back gear drive. Only the spindle pulley rotates around the spindle in back gear drive (and is locked to the back gear by a pin in direct drive). If there is a bushing in the back gear it can only be there for fitting the back gear to the spindle, not to act as a bearing surface because the back gear doesn't rotate around the spindle. No idea why the one in yours was worn, perhaps because the back gear had been run loose by a previous owner? Either way, as long as you're able to secure the back gear to the spindle at the correct spacing from the spindle pulley then you should be good.

Hey Matt...thanks for replying!
On my spindle assembly...my back gear (10-242) has 4 detents that the 4 drive dogs on the pulley assembly (10-79) fit into. Both assemblies spin freely on the shaft unless pin (10-256) in the back gear (bull gear) (10-241) is engaged with the pulley. On mine...10-241 is keyed to the spindle shaft and spindle drive comes from the pulley when pin 10-256 is engaged. I've never had it running yet but that's the way it seems to work.
I'll count my fingers before and after I power it up...just to be sure.
Thanks!
Bill

 

[Bill1958]

To clarify: the large Bull Gear is keyed to the spindle- we are referring to the spindle take off drive gear which is coupled to the pulley with dogs/lugs

Correct Sir!

 

[mattthemuppet2]

oh right, I got you now If they're sintered bronze I wouldn't worry about it, the oil added to the pulley oiling point will seep past (and into) the two spindle pulley bushings to oil the small gear bushing.

 

[Bill1958]

oh right, I got you now If they're sintered bronze I wouldn't worry about it, the oil added to the pulley oiling point will seep past (and into) the two spindle pulley bushings to oil the small gear bushing.

I'm not sure what the original bushings were...but the ones I'm installing are SAE 660 cast bronze...so they needs the oil.
Found them here at a pretty fair price if anyone's looking...you need to cut them to length. Was able to part them on my Unimat : )

https://www.bronzebushings.com/amfinder/?find=2--cast-bronze--cb--machined--sae-660-bearing-bronze-inch-sleeve-1-1-2-in-1-3-4-in-1-in-none-none-cb-2428-08-173400

 

[mattthemuppet2]

hmm, in that case I would suggest cutting (somehow) oil distribution grooves in each bearing to allow oil to get to the whole surface. It's going to be tricky as those types of bearings are more commonly stationary (think spindle bearings) with provision for an oiler or oiling system. Oilite or sintered bronze bushings are better for this kind of application with intermittent oiling.