bearing ID and OD for intermittent partial rotation side load application

[archibaldtuttle]

hopefully if all goes well there are a picture of a steering link and mounting post below. this is from small gray market japanese truck from 1991. newer models use bearings, oldermodels used bushing constructed of two steel collars bonded by rubber similar to a shock mount bushing.

parts and parts diagrams far and few between so i'm just trying to fill the space between the bore and post most sensible way i can. could be either roller/needle bearing or sleever bearing/bushing. very low use, just trying to get it below a half turn of play in the steering wheel.

for easy field application i'm trying to figure how close i can spec the ID and OD to the actual sizes of the bore and post. the bore currently is a little worn and i'd probably take it out to either 30 mm or 1.25 (currently avg. 1.160 so maybe it was 29 or 1 and 1/8 to start ??? and the post causes me a little more headache because it is turned down. the bottom third is just over 3/4 at .77 and the top is about .71.

my current set up is the old steel center collar with a 1" copper pipe pounded over it which gives me about 30 to 40 thousandths lash inside and outside. just trying to firm that up a little.

i'm not having great luck specing bearings because of the odd sizing. can i treat the .77 as if it were 20mm or is there an oversize 3/4. what would be standard clearance for field install. 10 thousandths difference in diameter or closer?

might be able to play with a few more copper sizes and slip fittings to limit the lash on the inside toward the post to 15 thousandths. and i could pretty readily have the bore taken up to 1.25 and that would leave no lash outside on a 1" copper slip coupling.

but i'm think it would be preferable to actually have a grease fitting and intend for the bushing to stay stationary, make it a little long and it with the nut like shoulder and then put a zerk fitting into the outside of the bore and overbore a bit to leave grease space. how much space should i leave for grease to keep play down but let grease in and insure that the rotation takes place along this surface . . .

this thing gets low use at low speeds on farm so i'm not worried about getting it to OEM specs, which apparently don't last long anyway as folks who handle used parts say these steering links are going all the time. and with this design i can always replace worn parts with copper pipe readily available that way. what would be advisable grease space. is there something wrong with copper as a sacrifical bushing in this application with virtually no rpms but levered side load. they always seem to use oil impregnated bronze but i'm got to go with what i got. i can't find any bronze that is going to do much for me and the copper built up from two pieces of pipe and two couples is pretty close.

sorry for the novel, was trying to include specifics and my design ideas.

brian

 

[Tmoose]

to me the post looks painted, as if all the rotation was happening has been happening elsewhere.
Is the post welded to the chassis, thus not readily replaceable? If so, it would make sense to clamp a snug fitting steel sleeve axially on the post, have bushings a press fit in the arm, and size the bushings for around 0.001" diametral clearance.

 

[archibaldtuttle]

tmoose,

thanks for taking a look a this repair. so .001 diametrical (so that means .0005 actual clearance on avg.?) is enough space for grease?


you are definitely right about the post. the turning has been taking place at the outside of the bushing assembly. they tell me the bushing assemblies on many of these japanese minitrucks are 3 piece sandwiches made up of a thinner outer steel sheel bonded to rubber bonded to an inner steel bushing.

if this assembly had outer steel, it was completely worn away, maybe it is deliberately soft material. and much of the rubber, esp. at the lower end of the joint was gone. i don't have the specs for the bore to know how much of the link arm itself may have worn in the process. it's not far out of round though. maybe 10 thousandths.

the setup you describe is actually pretty typical of the king pin arrangement in truck suspension. makes sense. i'll have the bore trued and press a bushing into it. assume that fit would be nominally identical. a 1.25 bore for a 1.25 bushing? I'm used to getting sets by application, not by measurement.

the bushing material is usually brass and i have expansion reamers to take it out evenly until it is .001 over whatever i can choose for a center bushing. what do you think about materials? don't see why brass wouldn't be appropriate.

as for a steel bushing to drop over the shaft, that is a little more complicated. i can't press anything on the center and it is going to be hard to get a bushing close to .77 shaft diameter. could get a .75 piece and bore it, but I'm thinking maybe i can go with 20mm which leaves a diametral clearance of about .0125 but use a strong steel bushing slightly longer than bore and it will be held still and straight by the nut on the shaft so i think that is why the center post is not worn (which is fortunate because its not readily replaceable or machinable.

thanks again,

brian

 

[Tmoose]

A bushing using rubber bonded to inner and outer sleeves (rubber in shear) is only capable of X degree rotation, like a suspension control arm. Way under 45 degrees I bet. If the angle is not too severe, and the radial stiffness is acceptable, bonded rubber bushings are a nice low maintenance solution.

I would favor a flavor of bronze with some lead in it over any of the fancy high strength bronzes since many of the high strength ones need gorgeous lubrication to survive.

Design of lubrication grooves and most importantly sealing will determine the life of the assembly.

m-a-y-b-e one of the fancy teflon filled bushings would be a decent choice, but investigation of PV values, surface finishes, and the not un-common requirement of rotating the parts dozens of times to transfer and distribute the fantastic plastic etc on the steel journal means the assembler needs to know and follow the process.