1958 Triumph Twenty-One - 2-Page Vintage Motorcycle Article

Description

1958 Triumph Twenty-One - 2-Page Vintage Motorcycle Article
Original, vintage magazine article
Page Size: Approx 8" x 11" (21 cm x 28 cm) (pages are front and back)
Condition: Good
NEW MODEL
FROM
COVENTRY
It was just twenty-one years ago that the
Triumph company was taken over by’ its
present management. To commemorate the
occasion of its “coming of age”, the Tri-
umph Engineering Co., Ltd. is launching on
the American market a completely new,
ultra-modern 350cc motorcycle aptly
named, for both the anniversary and its
displacement, the “Twenty-One”. Since the
larger part of the Triumph line comprises
machines of 500 and 650cc capacities, the
new 80 mph middleweight will fill the gap
between the 200 cc Tiger Cub and these
larger models.
Outstanding features of the new model
are unit construction of the engine and
gearbox, and comprehensive weather shield-
ing in the form of a well-contoured pressed-
steel enclosure on the rear half of the ma-
chine which supports a foam rubber twin-
seat. The Twenty-One has an overhead
valve, twin-cylinder four-stroke engine of
21 cu. in. (348 cc) capacity. Another at-
tractive feature is the inclusion within the
rear enclosure of such items as the oil tank
(a dipstick is provided), tool tray, car-
buretor air filter, battery, and most of the
electrical equipment. All these components
are neatly and compactly stored beneath the
twinseat. Both wheels are of 17 in. diame-
ter, typifying the current trend toward
smaller wheel sizes.
Embodied in the new 350 is the wealth
of experience in vertical twin design
amassed by the Triumph firm.
Technically, most interest will center
around the design of the unit construction
power-unit. The crankcase is in two parts,
split lengthways, and embraces both the
crankshaft assembly and gearbox. The gear
cluster is housed in its own compartment
with separate lubrication in the normal man-
ner. The whole engine/gear unit is remark-
ably clean: there are no awkward corners
to make cleaning a hard task. There is a
commendable lack of visible oil pipes and
control cables, and the distributor mounted
on the crankcase behind the timing side
cylinder has its leads and cap enclosed by
a rubber cover. Two slotted oil filler caps
for the gearbox and primary chaincases are
conveniently located on top of the engine
casing. The engine/gear unit is fitted in the
frame in such a way that removal is a sim-
ple and straightforward job. An interesting
feature of the gearbox design is that the
shafts and gears can be taken out without
disturbing the selection mechanism or the
engine in any way.
Bore and stroke dimensions of the Twen-
ty-One are 58.25 mm. and 65.5 mm. The
compression ratio is 7.5:1. A ball race
supports the drive side crankshaft and a
plain bearing of high duty material is em-
ployed for the timing side. Big-end bear-
ings are of the micro-babbit thinwall type.
An alloy cylinder head is fitted on a cast
iron cylinder block which has an alumin-
ized finish to match the head. Phillips
screws secure the rocker boxes and are
used for the primary chaincase outer casing.
The valves are pushrod operated from two
gear driven camshafts. Neatly tucked away
beneath the gas tank is the oil feed pipe
to the rocker gear—the only visible oil feed
above the engine.
The extensive enclosure of the rear half
of the new model together with a stylish
front mudguard of very generous propor-
tions gives excellent rider and machine pro-
tection from road dirt. That the oil tank
is concealed inside the "bodywork” is an-
11206-5712-04