H rod bearings

does any know why JD switched from inserts to babbitt bearings on model H connecting rods

I thought they were always babbitt.

From the beginning through S/N 21499, H tractors were equipped with insert-type rod bearings, and almost immediately bold warnings started appearing in the Field Service Bulletins such as the one pictured below.

Then, starting with S/N 21500, babbitted rods replaced the insert versions. Per a note in Field Service Bulletin 115-S which announced the change, the claim was made it was because it would .provide shim adjustment for taking up wear in connecting rod bearings rather than replacing the bearing shell as was necessary with the steel backed replaceable shell type bearing.

In those days, lubricating oils were not great, there was dilution of oil from distillate fuels, marginal oil filtering, etc., so wear of journal-type bearings and crankshafts were rather pronounced and swift. Mechanics were familiar removing shims to compensate for bearing wear and from the warnings it appears it was a common error to file off the rod cap mating surface to compensate for wear. So, perhaps Deere felt it was too modern of a design for the time and fell back into the old familiar and proven babbitted bearings with shim adjustment configuration.

can i update from babbett to insert rods, are inserts available .005-.010-.020 now that we have better oils and filters

You can substitute babbitted rods for insert-bearing-type rods and vice-versa. I don't know much about availability of inserts. Deere still offers standard size inserts (P/N AH662R), and at one time offered .005 inserts, but those don't show up in their online parts search. There's a possibility that some manufacturer makes various sizes of insert bearings that will fit those older rods. There's nothing wrong with babbitted rods and there are several places that will re-babbitt and resize rods for you.