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Santa Train is the Northwest Railway Museum’s annual family event held after Thanksgiving.  First hosted in 1969, this seasonal excursion has become a tradition for thousands of Northwest families.

Locomotive 4012 as it arrived in 2000.
4012 was acquired from the Yakima.

While preparing for this year’s event, an engine crew caught locomotive 4012 being a little too much in the spirit of the season: it was a emitting a sound strangely similar to the Ghost of Christmas Past from Dickens’ A Christmas Carol.  The 4012 is a 1953-built Baldwin-Lima-Hamilton RS4-TC that has operated for the Museum for many years.  It has been a very reliable locomotive and has rarely been out of service.  A quick assessment found that the culprit was the engine cooling fan, which had suffered a partial failure.

The cooling fan is an important part of any diesel engine.  On the 4012, it is powered with the diesel engine by coupling a universal joint to the end of the engine driveshaft.  The universal transmits power to an angle drive and the cast aluminum blades are mounted directly on top. The speed of the fan is directly proportional to the speed of the diesel engine.  

After the fan drive was disassembled, the problem was evident: a number of gear teeth had stripped off one of the miter gears.  So each rotation of the shaft caused the gear to slip, which also damaged the universal joint.  If left unchecked, continued use would have stripped all the teeth off the gear and resulted in an overheated diesel.

Broaching a keyway.

Fortunately, an identical  6 diametrical pitch, 30 tooth, 45 degree miter gear with a 20 degree pressure angle was available from a gear manufacturer.  Unfortunately, the bore was too small for the existing driveshaft.  So Curator Pappas has his work cut out for him.

Gear mounted on shaft.

Using the Museum’s Monarch engine lathe, the bore was enlarged.  The second step was broaching a keyway in the bore to engage the key
present in the shaft to assure power transmission rather than slipping.
 Rather than purchase an expensive broaching set or contracting this work out,
this was handily achieved by grinding a broaching single point tool and running
it on a boring bar by hand with the lathe carriage.  This yielded a
perfect keyway that needed no hand fitting.  The final step was facing the
hub of the bear so as to set the lash.  The gear pressed on the shaft with
no problems and the gearbox has been reassembled.

A test run of the 4012 quickly established that everything was correctly fitted.  Now locomotive 4012 is ready to pull nine days of regular Santa Train 2014 to North Bend, and to support steam locomotive SCPC 2 on the special Friday, December 19 Steam Santa Train. 


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