Borbin the 🐱

Not only have the CJ750 and M72 the same final drive (the thingy that connects the back wheel to the gearbox), but they also share the same Ring and Pinion gear of the Ural Motorcycle.
With the Ural 2019 and newer, final drives now running an European Ring and Pinion gear. Here I show you how to use those to upgrade your final drive (FD). So no more Russian or Chinese Junk!
See the Interview with Ural on youTube starting from 0:23 with details on the new gear set.

The European Ring and Pinion set is IMZ-8.128-05048 and has a 37/8 ratio.

Left side is my old one. Right side is the new one from the Italian production. Italians are specialized in flat round things (Pizza).

Bottom is the new one.

Bearings:

Ring bearing 6207c3

(35mm bore, 72mm OD, 17mm width)

Pinion bearing 3304

Bearings can have different properties. For example:
3304 A-2Z/C3
Angular contact ball bearings, double row
- 2Z: Shield on both sides (Z is for metal shield)
- C3: Internal clearance greater than Normal

3304 A-2RS1
Angular contact ball bearings, double row
- 2RS1: Contact seal, NBR, on both sides (RS is for rubber seal)

C2: Clearance less than normal clearance
C1: Clearance less than C2 clearance
C3: Clearance more than normal clearance
C4: Clearance more than C3 clearance
C5: Clearance more than C4 clearance

3304 A-TN9
TN9: Glass fibre reinforced PA66 cage, rolling element centered

The 3304 gets pressed on later to the pinion gear shaft. For the contact pattern, a plastic guide with the same dimensions as the bearing is used to make it easier to move the gear in and out of the casing.

The following places are a good source if you want to start with new parts. I have used them all and they provided exceptional service.
- ural-zentrale
- oldtimergarage
- sidecarpro
- mhmotoworld ebay or mhmotoworld

Please be aware that shipping damage can happen despite the best efforts of the packaging. Like this bend, which is a quick fix. Project on!

Note: The M72 has only one stabilization fin on the housing, while the CJ750 has two as seen in this picture to make the housing more stable. But in general parts are exchangeable.

Inspect all parts, and make sure all oil channels are clear.
The oil drain from the main seal to the bottom is most important. It prevents oil contaminating the break shoes.

FDs consumables. My collection.

Pinion inner bearing

The pinion inner bearing is normally 20x32x20, but with the new pinion it needs to be 20x32x16. This is a NKI20/16 Needle Roller Bearing.

The existing pinion gear race in the FD needs to be removed. A simple task using a Blind Hole Puller (from a Blind Hole Collet Bearing Race and Seal Puller Extractor Kit in case you are looking for such puller), and a piece of protecting plastic.

Make sure the tiny hole to the main bearing is also clear.