The plastic tub of the Graupner PistenBully is starting to show its age. Due to embrittlement of the material fractures may occur. Especially the flange of the powered shaft is under high load. Therefore we added an aluminum L-profile (10x10x2 mm) to distribute the load on the two forward positioned axle flanges at our Graupner. The aluminum profile was filed to fit the axle flanges. This drawing (PDF) may serve as a starting point.
The strengthening fins of the flanges have to be filed flat in those areas where the aluminum profile will rest. For better adhesion roughen the surface of the aluminum and plastic with 150 grain sand paper in those areas where glue will be applied. Thoroughly decrease and glue in place with 2-component epoxy.
One of the gears of the 3rd gear set was destroyed at our Graupner PistenBully, after the shaft blocked. To avoid this regular greasing of the bearings should be done. The Graupner gears are module 0.75, which is not part of the preferred DIN standard and as such hard to get. A fitting gear set for the given shaft distance is possible with module 0.7 and 14/35 teeth. The small change in gear ratio is towards slower speed, which adds some torque. The mis-match of the shaft distance is only 0.1 mm. Such gears are available at Maedler.
The holes of the gears have to be adjusted on a lathe. The plastic gear has an inner bore of 7.5 mm and is pressed on a reeded shaft, which can easily be done on a vise. The brass gear has a 4 mm hole and got a M3-thread for the worm bolt.
The damaged plastic gear was reduced step by step on the lathe until only a small sleeve was left, which was cut with a knife and removed.
Repaired gear box with new gear set
We scanned the original building instructions which also include maintenance advice. It’s available for download as PDF by clicking on the image. The Graupner PistenBully was marketed as “The Blizzard” outside of German speaking countries.
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