Cat 20 final drive preload

My Thirty manual says to "screw the sprocket hub bearing adjusting nut on as tightly as it will go, and then back it off two notches to allow bearing clearance." When I rebuilt the final drives of my Cletrac HG, the manual had an actual force specification that I measured with a fishing scale. I'd be interested to know if someone has this number for the Twenty and where they got it.

Wyocat,

Yes it is the sprocket /bullgear hub that I'm setting the preload on. It is shim adjusted on the outer bearing but there is no spec in the book that I can find. It appears that the 10,15's have the adjustment on the end of the dead axle which is adjusted by the large nut. ( of which some endfloat is required )
The 22,25,28 looks to be adjusted by a large nut on the outer part of the outer support bearing. ( totally different set up to the "20" ).The cat 30 is nut adjusted not shim adjusted but the details in the book are rather vague. It just mensions doing the preload but not saying to what spec to do it to.
It appears that the 10,15,22,25,28 have "some " endfloat in the sprocket hub brg setup.
One would assume that some "endfloat " is required for the sprocket hub brg's.


Are there any other thoughts out there on this matter?

Speak up! LOL

Cheers djcat

Any that I have taken apart did not have any "end float". I am guessing that this term means endplay. I have never done a PL 20 but any of them with the nut design I use a dial indicator. As I tighten the nut I continually check endplay with the dial indicator. Keep in mind I also rotate the shaft as I am tightening the nut as to help seat the bearing rollers. Once I get to the point where I only have approx .005" of endplay I know that by tightening the nut to the next slot for the cotter pin is just about perfect. I always rotate the shaft quite a few times and recheck for endplay. One slot on the nut is not all that much axial movement so I know that I am not putting too much preload on the bearings. Whether it is right or wrong this is how I do it. I know by keeping the shaft still from any radial movement will help the entire final drive, by keeping the gear still and will provide a stable surface for the bellows seal to seal against since the sprocket will not be moving in any strange directions.

Here is the confusing part about bearings. Any bearing manufacturer will tell you that a bearing will last longer preloaded vs. having endplay. Endplay can easily be measured while preload is a guesstimate or a calculated amount. Preload increases very quickly, so a little will be just fine. I hope this helps someone out there. Alot of this old stuff just takes common sense. If the shaft turns hard, there is something wrong. Good luck!!

DJ - If I'm reading this right .. just looking at the sales brochure, and not the parts book .. the sprocket bearings are two taper rollers, and the preload on the "L" Twenty, is merely adjusted by the outer, dead axle nut?

[img]http://i36.tinypic.com/98x4xh.jpg[/img]

Bearing manufacturers have nearly always recommended a certain amount of bearing preload on heavily loaded taper roller bearings .. particularly under severe service, and where shock loadings are prevalent (as in final drives).

In the early days (we're talking 1927, when the "L" Twenty was released), I think you'll find that exact taper roller bearing preload, under heavy load, wasn't as well understood, as it became in later years.

Thus, there is no reference to any exact bearing preloads (usually measured with a string and spring scale) in early manuals. I believe that the engineers at Cletrac, A-C and other manufacturers were onto specified bearing preloads, before Cat engineers were. Final drives bearing preloads are virtually impossible to measure with a spring scale, due to the associated component drag.

The general rule of thumb I have always used .. is that low speed, heavily loaded taper rollers receive a modest degree of preload (to exact measurements if specified) .. but taper rollers that are high speed and relatively lighter loaded, such as wheel bearings, receive very little preload.
Many Cat manuals only specify a certain nut torque, without any reference to spring scale measurements .. unlike many other tractor manufacturers.
You need to remember that any clearance in bearings such as final drive bearings, creates a "hammering" effect on the rollers, when shock loading is encountered.
The greater the clearance, the greater the hammering effect, and the shorter the bearing life.

The bearing manufacturers give you preload/clearance tolerances for their specific bearings, and these tolerances can be quite wide, ranging from clearance to modest preload.
Here's a webpage with a lot of useful information on taper roller bearings ..

http://www.bearingstrade.com/taper-roller-bearings.html

OzDozer
Thanks for the information, you have more common sense about mechanical stuff in general then most That visit this board, THANKS!😊
Frank Fox

OZD,

The sprocket shaft is stepped on the left side of the outer brg as shown in your pic. There are shims used between the outer brg and the pivot brg holder that pushes up against the outer sprocket hub brg. By adjusting the number of shims will give you either preload or end float. The dead axle nut mearly holds everything tight up against the shims. Hope that makes sense..LOL


Cheers djcat.

DJ - Are you saying that the nut pulls the pivot bearing holder up tight against the step in the sprocket shaft? .. and that the bearing preload/end play is only regulated, by the number of shims? 😕

In the pic above, the pivot bearing holder is not shown as being hard up against the step in the sprocket shaft .. and it appears that the preload/end play is only regulated by the position of the nut.