Harrison Machine Works Boiler and Steam Engine Construction Techniques


| September/October 1995



Axle and Bracket

Jumbo Axle and Bracket

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.