Series A Hubs
This month I want to focus on the Series’A’ hub assembly. The hub is markedly different from
the hubs fitted to later Series. The general arrangement of the hub assembly is set out in
Illustration 1.
The hub body is made of (cast) aluminium alloy and measures 3.375” in diameter and 3.50” in
length. Of the length there are 2 spigots each of length 0.375”, and with a diameter of 2”. The
spoke flanges fit over the spigots and are 0.125” in depth. The brake drums come next, followed
by the hub bearing housings. The hub studs, which pass completely through the hub body, spoke
flanges, brake drums, and the hub bearing housings, are length 4.75”, and are secured by special
nuts (730/1); the hub studs are arranged with a PCD of 2.75”; the threads are 5/16” CEI.
The brake drums are steel pressings, approx. 0.130” in depth.
The hub bearing housing is 1.1/32” in depth, and has an outside diam. of 3.375”; it has an inside
diam. of 1.938” to take the bearings, on the inside this diameter is increased to 2” for a depth of
3/16” to clear the spigots.
The hollow axle passes through the hub body, the bearings, and the brake plate, it is 5.15/16”6.031” in length and has an OD of ¾”, and the ID is 0.5”. Incidentally it is the same length as the
distance between the fork legs on pre-war Brampton forks (6.031”).
The original fitting was an outer sleeve that slides over the hollow axle and provides for shims
between the bearing and the outer sleeve. The length was approx. 3.6” (two different samples
had lengths 3.19/32” and 3.5/8”) and had a OD of 15/16” and an ID of ¾”. Note that this is quite
rare now, apparently the factory made a modification to the hollow axle and outer sleeve so they
were combined into the more familiar type (i.e. the shouldered type as found on later Series) and
owners fitted these..
The bearing outer cups fit into the hub bearing housing and fit against the spigots. The bearing
cones fit against the outer sleeve (or the composite type of hollow axle), with shims as necessary
to control the end-float. Note the bearings are the same type as used on early Series ‘B’ and ‘C’,
and have dimensions of ¾” x 1.938” x 29/32”.
If necessary, shims are fitted between the brake plate and the bearing.
The brake plate are approx.0.140” in depth (so they are deeper than the post-war models).
The front and rear hub assemblies are identical. The rear hub assembly uses two cam bush
steadies fitted OUTSIDE of the E80 nuts. Note that the only parts which share a commonality
with the later Series are the bearings, the shims, the felt washers, and the nuts(E80).
Illustration 2 shows a section drawing of the hub assembly.
4
3
2
1
D
D
Thin nut(E80)
2 off
Outer sleeve
Hub stud nut(730/1)
10 off
Spoke flange(H2)
2 off
Felt (H47)
2 off
Hub stud(H19)
5 off
C
C
Shim(H17)
as required
Hollow axle(H15)
Hub body (H38)
Bearing(H22)
2 off
Hub bearing housing(H3)
2 off
B
B
brake plate
goes here
brake drum
goes here
DRAWN
Bill
1/4/2015
CHECKED
QA
A
TITLE
A
MFG
APPROVED
SIZE
C
SCALE
4
3
2
REV
DWG NO
hubillust
SHEET
1
1 OF 1
4
3
.25
D
cambush steady
only on rear hub
sits against the E80 nuts
.50
.937
1
R.438
D
1.124
2.65
.188
.50
2
.125
.187
1.182
.125
shims go here
between bearing
and outer sleeve
(on both sides)
DETAIL C
SCALE 4
A
C
C
C
6.031
outer sleeve
B
B
SECTION A-A
SCALE 1 : 1
Notes
as shown on the drawing the length of the hollow axle=6.031"
but in actual fact it is somewhat shorter, 5.9375"
A
DRAWN
Bill
the bearings used are SKF K9074/K9196 (H22), width=0.90625"
(the W5413 bearings are 0.9375" wide, i.e . 1/32" wider, so
making up the space between the bearing and the brake plate)
10/27/2014
CHECKED
QA
on Marcus's RFM the distance between the fork ends=7.125"
if you add two cambush steady's the the total width =7.031"
TITLE
MFG
APPROVED
the brake plates need to have a hole (tapped 1/4" BSF) approx.
1.125" from the centre in line with the cambush steady on the
opposite side to the cambush steady; for the brake plate used
on the front left this hole needs to blocked by a bolt
4
SIZE
C
SCALE
3
2
Hub and brake assembly
front and rear
Series A
A
REV
DWG NO
dimfronthub2m
SHEET
1
1 OF 1