NU - cylindrical roller bearing
306 - width and diameter series
E - (two piece bearing??)
M - Brass Cage (TVP - polyamide cage)
C3 - Radial internal clearance greater than normal
What you list is not really three different bearings, just that the first two do not give the internal clearance code (CN, C2, C3, C4) and number 1 and 3 do not specify the cage type, polyamide or brass.
I only use the brass cage bearing, but I can't really see why the polyamide would not be as good. The main bearings I use are C3 clearance.
Cylindrical roller bearings, single row come with designations NU, NJ, NUP,
The various designs of cylindrical roller bearings are distinguished by the
arrangement of their lips. Design NU has two lips on the outer ring, the
inner ring being lipless. The inner ring of design N has two lips, the outer
ring has none. Cylindrical bearings of design N and NU are used as floating
bearings. They are seperable which simplifies mounting and dismounting, both
rings can be fitted tightly.
Cylindrical roller bearing NJ has two lips on the outer ring and one lip on
the inner ring. They can accomodate axial loads in one direction.
Cylindrical roller bearings NUP are installed as locating bearings to
accomodate reversing axial forces. They have two lips on the outer ring and
one fixed lip and one loose lip on the inner ring. A cylindrical roller
bearing NJ with an angle ring HJ forms a locating bearing similar to NUP.
Single row FAG cylindrical roller bearings of the basic design have normal
Bearings suffixed C3 (radial clearance larger than normal) or C4 (radial
clearance larger than C3) are available on request.
The modified line contact between rollers and raceways of the cylindrical
roller bearings eliminates edge stressing and ensures a certain aligning
capability. The angular alignment of single row cylindricl roller bearings
must not exceed a maximum of 4 angular minutes at a load ratio of P/C<=0.2
(P= equivalent dynamic load[kN], C=dynamic load rating [kN].
The suffix M and M1 indicate bearings with roller-riding machined brass
cages. (German word for brass is Messing)
This is the info straight out of and word for word from the FAG cattledog.
You can see the E series cylindrical roller bearings, or so called super
blend secret is in the alignment paragraph which tells about an allowance
for the rollers to have a 4 minutes (as in degrees, minutes & seconds of
angular measurement) of misalignment and the edges of the rollers are
modified to have less edge stress along with that misalignment. In other
words this will make some allowance for the dreaded Commando crankshaft
The NU (two lips) will be written on the outer ring and the NJ (single lip)
will be written on the inner ring of the bearing you need for your Norton.
I have recently pulled apart a high mileage very well used well known
Commando motor with a non FAG NJ306 (no 'E')cylindrical roller on the drive
and a 6306 ball bearing on the timing side. The ball bearing failed, but
still had the seals in the bearing and was probably the reason why the
bearing failed. Had the seals been removed to allow fresh lubricant into the
bearing it may well have still been ok, who knows. Various other main
bearings from other reputable makers are available, as far as I know, FAG
are the only manufacturer who offer a brass cage, most others offer the
NJ306E with steel cages or indeed glass fibre reinforced polyamide 66 cages.
FAG NJ306E C3 are the socially acceptable bearing to use. They are the
bearings used as a spare part from Norton and are the proven product. If you
use another brand, don't tell anyone as this is akin to murdering your
grandmother and everyone will think your a dill and no one will talk to you.
Hunt for prices on the FAG items as they can be very expensive to someone
straight off the street. I have seen them as cheap as $50 each and have
heard they can be over $250 each. If you can only get them for a ridiculous
price, then come back to the list and ask if anyone can get them for a