Totally confused about M38A1 Front Spindle Bushings

[Granny]

Hopefully, some of you guys familiar with the old stuff can set me straight on this one.....

Having spent over 50 years of my life in a machine shop I recently came across a situation that basically defies all the knowledge that I have gleaned during that time...

I was helping a good friend replace the brass bushings in a pair of 1957 M38A1 front wheel spindles. The new bushing OD measured approximately .020" larger than the bore. The Kaiser/Willys parts rep told my friend that the .020" press fit was correct and they would fit. Well... I bet my 50+ years of know-how that the bushing would buckle before it got 1/4 of the way in the bore. And... I was wrong... it went just fine... it did not buckle or crush... but, the ID did taper somewhat. It does fit the axle, and appears it will work just fine.

It is my very strong belief that .001" press would have accomplished the same thing and would not have tapered the bushing. can any one of you experienced guys/gals please provide some details and set me straight on this?

You already know you're appreciated!!!

 

[Croatan_Kid]

Wow... .020? I would have figured .010 max, but definitely more than .001. I'm not even sure how you got it to start and not roll the hell out of some metal if the bushing OD was .020 bigger than the ID of the hole.

Got a picture of the assembly?

 

[Falko]

We have an assembly at work that sometimes uses a brass based powdered metal bushing, and sometimes uses a carburized steel bushing. The nominal press fit on the steel is ~.006 and the press on the powdered bushing is ~.024.

They end up requiring the same force to press in, which mean the retention force in the housing is near equivalent. It's all about the elastic modulus both bushing and housing.

The free machined dimensions of each bushing are obviously different to achieve the same assembly dimension once pressed in.

 

[Granny]

We seem to be thinking pretty much alike on this. Personally, I would not put more than .001"-.0015" press on a bushing like this. I just don't believe that .020" press on a bushing with this thin of a wall will hold it any tighter than .001" will. I would still like to hear a technically sound reason for this from someone who is actually into the know-how of it... and I am already thinking of a couple of you.

Got a picture of the assembly?

No picture, but...

Spindle: Front Axle Spindle Fits 41-71 Jeep & Willys with Dana 25/27

Bushing: Front Axle Bronze Spindle Bushing with Flange Fits 41-71 Jeep & Willys with Dana 25/27

 

[Fabrik8]

You're right, a lower press fit would not have tapered the bushing, but there's obviously some reason that they're using such a high press fit. The alloy of bronze being used, and whether it's a porous Oilite-type bushing, will set the press fit tolerance, as well as the bushing geometry (wall thickness, etc) and the type of loading. A softer material and thinner wall will need a greater press fit to properly retain the bushing versus something like steel, and also the same types of material properties for the housing and for the housing geometry. Same stuff as already mentioned above. The bushing diameter also matters, as press fits are often a certain amount per bushing diameter (like 0.001 inch per inch diameter, just pulling made-up numbers out of my butt).

Usually a heavier than normal press fit (for a given material, etc.) is used for high loads or cyclic/rotating loads, to keep the bushing from moving in the bore (either sliding or rotating, depending...). It's a similar principle as bolt preload; the bolt preload has to be greater than the total amplitude of a cyclic load, else the load on the bolt can approach zero and fail from fatigue (repeated cycles from zero to loaded) or lose clamp force and stop sealing if it's a head bolt or whatever. So heavier loads in variable locations around the bore would normally need a higher press fit to keep the bushing from unloading and moving. Don't really know if that applies to your application or not though, it's just common bushing theory.

Is that axle bushing actually loaded very much? I don't really know anything about these spindles or what the purpose of the bushing is. Looks like it would just retain the axle or keep it from walking around, like the function of a C-clip (is that why the bushing is flanged)?

 

[WARRIORWELDING]

I'm picking up what your putting down.....think compression and roll forming.
Like rolling out aluminum to a smaller thickness which also work hardens the material. Being a very similar alloy I can see this being doable and actually gain some practical advantages in compressing the material.
Also in the area of operation.....this press fit would be field repairable, maintainable without anything more special than something to press it together. No special procedure, tools, or set up to follow. Send it home and your done.

 

[WARRIORWELDING]

Simpler thinking....softer material and easier to compress. More interference required to achieve the same psi load to retain without aditional retaining methods.

 

[Caver Dave]

Back when folks repaired OPE/small engines, most of the bronze-ish repair bushings in a cheaper B&S/Tecumseh (the output sides had bearings on the better engines) were like that... ream to enlarge the ID, press (hammer) in, and then ream to assure the alignment top/bottom (vertical) or side/side (horizontal)