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Artist drawing of CPR No. 229, Mastodon.

Mastodon 4-8-0 Steam Locomotive
Mastodon was the unofficial name of the Central Pacific Railroad's number 229, the world's first successful 4-8-0 steam locomotive.

History and career
The engine was designed and built by the road's master mechanic, Andrew Jackson "A.J" Stevens at Sacramento Locomotive Works in 1882. The locomotive had two highly unusual features: the firebox shape and the steam distribution.

The rear part of the firebox was depressed so that the outer shell was below the water level, leaving no clear steam space, and the roof  sloped downward towards the back so that steam bubbles would flow forward until they reached the upper vertical part of the backplate which was in two pieces. The fire-hole door was in the lower backplate, and the firebox was very long, measuring 13 ft-4 3⁄4 in (4.08 m) to the tubeplate, the grate being 9 ft (2.74 m) long. It is not clear what object Stevens had in mind when he disigned this construction, however, it was probably costly to build and maintain. One thing is for certain, it did allow more room in the cab.

The special valve gear operated four slide valves for each cylinder, two of which were worked by Stephenson valve gear, but used for reversing only, and two more, on top of the first two, for controlling the cutoff, these being operated by a third eccentric through a rocking lever with a sliding block on one arm. The use of a double valve gear is reminiscent of Centipede, but separate valves for each end of the cylinder were novel on a locomotive. This valve gear gave very good steam distribution even at short cut-offs; short as understood for a saturated-steam engine with a boiler pressure low by modern standards. At long cut-off and a speed of 8 miles per hour (13 km/h) the indicated mean effective pressure was 124 lb/sq in (8.7 kg/cm2; 850 kPa), which is over 91 per cent of the boiler pressure of 135 lb/sq in (9.5 kg/cm2; 930 kPa), that is to say more than the 85 percent normally used to calculate the tractive effort at starting.

The only other locomotives to use such a valve gear were the 20 copies of Mastodon and CPR No. 237 "El Gobernador". All other steam locomotives with slide valves had just a single valve in the center.

After being readied for its initial shakedown run, the engine met with a minor mishap in which its large "balloon" stack was knocked away from the boiler. During all the careful preparations, apparently nobody noticed that the stack was nearly one foot (0.305 m) taller than the doors to the roundhouse. The problem was fixed and an impressive series of trials on the steep grades of the Sierra Nevada soon followed, in which it easily outperformed the smaller 4-4-0 and 4-6-0 engines used by the railroad in those days. Later, Mastodon was sent east to the Cooke Locomotive and Machine Works, along with blueprints and men who had built the engine, where more than 20 copies were produced; these were identical except for having their cylinder bore increased to 20 inches (508 mm) (from Mastodon's 19 inches or 483 millimeters). The success of this engine inspired railroad president Leland Stanford to instruct Stevens to build an even larger locomotive, which would be the largest the world had ever seen up until that time. This engine, a 4-10-0 named El Gobernador (CPRR No. 237), looked virtually identical to Mastodon, with the exception of being longer and having an additional pair of driving wheels. Unfortunately, this engine, unlike its predecessor, was doomed to failure.

Sometime in the early 20th century, No. 229 (now renumbered as Southern Pacific 2925) was converted from wood to oil-firing and was later assigned to the Oregon lines. Despite its historical significance, the engine was broken up for scrap at the Brooklyn Shops in Portland, Oregon, in June 1935.

Mastodon Overview
Type and origin
Power type: Steam
Builder: Central Pacific's Sacramento, California, shops
Serial number: 20
Build date: April 1882
Configuration: 4-8-0
Gauge: 4 ft 8 1⁄2 in (1,435 mm) standard gauge
Driver diameter: 55 in (1,397 mm)
Adhesive weight: 81,000 lb (37,000 kg)
Locomotive weight: 105,850 lb (48,010 kg)
Fuel capacity: 10,700 lb (4,900 kg)
Water capacity: 2,500 gal (9,500 l; 2,100 imp gal)
Boiler pressure: 135 psi (930 kPa)
Heating surface: 1,355.3 sq ft (125.91 m2)
Cylinder size: 19 in × 30 in (483 mm × 762 mm) diameter × stroke
Performance figures
Tractive effort: 22,595 lbf (100,510 N)
Operators: Central Pacific, Southern Pacific
Numbers: 229; renumbered 1950 in 1891; renumbered 2800 in 1901; renumbered 2925 in 1906.
Nickname: Mastodon
First run: April 1882
Disposition: Scrapped June 29, 1935, Brooklyn shops, Portland, Oregon.

See also:

4-8-0 Mastodon

N&W Class M

Steam Locomotives


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Artist drawing of CPR No. 229, "Mastodon."

Central Pacific logo.