Harrison Machine Works Boiler and Steam Engine Construction Techniques

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Jumbo Axle and Bracket
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FIG. 15. THE CROSS-HEAD
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The 20 H. P. Jumbo Steam Traction Engine, Fly Wheel side-Rated H. P. 20, Brake H. P. 65

R. D. #13, Box 209 Brazil, Indiana 47834

Harrison Machine Works produced boilers for their
‘Jumbo’ engines in their own boiler shop. The shell was
rolled from 5/16‘ flange steel with the
seams being double riveted. Each sheer was stamped with its tensile
strength which ranged from 55,000 to 65,000 per square inch. The 15
and 17 HP Jumbo boilers were 30′ diameter and 20 HP boilers
were 35’. The 15 and 17 HP boilers had forty-one 2′ x
78′ flues and the 20 HP boilers had fifty-six 2′ x 78′
flues. The smoke box was independently rolled and attached to the
boiler with butt straps so it could be easily replaced if needed.
Each boiler built was several horsepower larger than its shop
rating.

Firebox construction was of the open bottom type with the inner
and outer walls riveted to a heavy cast mud ring. The crown sheet
was rounded at the top and slopes toward the rear. The sloping top
was to prevent the crown sheet from being uncovered when going down
hill and melting out the safety plug located in the top of the
firebox. A space of 12 to 14 inches was left over the crown sheet
to prevent foaming. The fire box was braced with
7/8‘ stay bolts and the bottom of the ash
pan has 16’ road clearance.

The rear axle was attached to the boiler with nine ‘ cap
screws arranged in a circle. The bottom of the axle bracket was
attached to the mud ring with three 7/8
cap screws to cause the mud ring to bear the sup port strain and
not the boiler. The axle spindle was cast into the bracket on a
taper and riveted over to cause the axle to be tightly drawn into
the bracket. If replacement of the spindle was necessary, the
riveted-over end could be chipped away, the old axle driven out and
a new one driven in and riveted over.

Jumbo drivers (or rear wheels) have a diameter of 78′ with
16′ or 18′ face rims to which an 8′ extension could be
added. The drivers were cast solid with the heavy hub being cast
after the rim to allow natural shrinkage to tighten the rim.
According to company publications, spokes on a Jumbo wheel do not
loosen up.

The engine frame is of the Corliss type with the guide and
pillow block cast in one piece. The piston was cast of grey iron
with a cored center to reduce weight and consequent weare on the
cylinder. The piston is 3′ wide with two snap rings each
7/8‘ wide. The piston rod is 1’
diameter and driven into the piston on a taper. The cross head was
cast steel with two adjustable cross head shoes or gibbs. The
diameter of the cross head may be increased a quarter of an inch by
loosening a nut and driving the gibb forward or backward. This
adjustment being possible due to the taper on the gibb bearing. The
pit man rod is forged from Norway iron with keyed adjustable bronze
boxes. The keys are arranged so that one lengthens and the other
shortens the pitman. The wrist pin is made of tool steel, tapered
and riveted over allowing it to be easily replaced. The crank disc
is made of carbon steel; pressed on and keyed to the main
shaft.

The throttle has balanced roller valves which allows the rollers
to un cover all steam ports simultaneously. This action can occur
on either for ward or backward movement of the reverse lever which
makes it possible to operate the throttle and reverse lever
together and eliminate one lever for the operator.

The flywheel operates at 235 rpm and is 40′ in diameter. The
15 x 17 HP have a 10′ crowned face and the 20′ has a
12′ crowned face. The friction clutch has a heavy balanced
spider equipped with six white oak shoes which are boiled in
linseed oil.

The two speed device which is found only on Jumbo engines
consists primarily of a high and low speed gear. The low speed gear
is riveted to the clutch spider, and the high speed gear slides
over the low speed gear, being connected to the clutch by means of
three triple tooth lugs cast on the spider. The power transmission
from either gear is accomplished by an intermediate gear, which
operates on a sliding segment. The sliding segment is controlled by
a lever working in a notched quadrant with three positions: high,
low, and disengaged. The sliding segment is disengaged by means of
the lever operating the sliding segment. The high speed gear is
unlocked and moved over the low speed pinion, locked in this
position and the inter mediate gear engaged by moving the shift
lever to the high speed notch in the quadrant. In low gear, the
speed is 2 mph and the high gear is 4 to 5 mph. When doing clutch
work the intermediate gear can be disengaged, allowing the clutch
to revolve with the flywheel giving added momentum to the flywheel
and eliminating clutch drag. The intermediate gear is located above
the centers of the speed gears and the equalizing gear, exerting no
strain on the sliding segment journal.

This (hopefully interesting) information is based on factory
material for 15,17, and 20 HP Jumbo engines. I’m compiling a
list of Jumbo engines and Harrison Machine Works equipment and
would like anyone with information to contact me.

DIMENSIONS OF BOILERS AND ENGINES

The following table shows the specifications of Jumbo Engines.
We reserve the right to make such changes, without notice, which
will, in our opinion, constitute an improvement in our
Machinery.

PARTS

JUMBO TRACTION ENGINE

15-Horse

17-Horse

20 Horse

Diameter of
cylinder……………………………………….

77/8 Inches

8 Inches

8 Inches

Stroke of
cylinder…………………………………………..

11 ‘

11 ‘

11 ‘

Speed of Fly
Wheel………………………………………..

235 R. P. M.

235 R. P. M.

235 R. P. M.

Diameter of
Boiler…………………………………………..

30 Inches

30 Inches

35 Inches

Length of
Boiler……………………………………………..

136 ‘

144 ‘

152 ‘

Height of
fire-box……………………………………………

33 ‘

33 ‘

40 ‘

Width of
fire-box……………………………………………

26 ‘

26 ‘

30 ‘

Length of
fire-box…………………………………………..

40 ‘

40 ‘

45 ‘

Length of
flues……………………………………………….

70 ‘

78 ‘

78 ‘

Diameter of
flues……………………………………………

2 ‘

2 ‘

2 ‘

Number of
flues…………………………………………….

41 ‘

41 ‘

56 ‘

Height of dome………………
…………………………….

24 ‘

24 ‘

24 ‘

Diameter of
dome………………………………………….

16 ‘

16 ‘

18 ‘

Diameter of driving
pulley………………………………..

40 ‘

40 ‘

40 ‘

Face of driving pulley……….
……………………………

10 ‘

10 ‘

12 ‘

Height of traction
wheel………………………………….

78 ‘

78 ‘

78 ‘

Face of traction
wheel……………………………………

16 ‘

16 ‘

20 ‘

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