trackdoc, the one that failed was S/N 7TR02736. The gear is a 153-1243 - been in use since 1998. It's been replaced by 420-2042 since mid-2012. A new gear is about $300, so we're now replacing all of them (every engine we have bar one has the former Part Number gear) as a one time only deal with the new gear when we pull them for overhaul. Previously that gear was only replaced based on condition when the engine was overhauled at 20k hours. The main problem we have is a number of engines that have already had 1st overhaul - what do we do with the gears in them..?
Don't get too wound up, the failure mode is sporadic (allegedly) but since we've had the failure it's focused our efforts wonderfully.
Mitch, they are actually an air turbine starter motor bolted into the flywheel housing. One TDI Turbostart will replace 2 x 50MT electric starters and is about 1/10th of the weight. Why anyone would want to use electric start (including the 6 8D batteries it needs - the air start version of the truck uses 2 x 4D simply to light up the dash panel) on an engine this big I have no idea.
http://tdi-airstarter.com/t50.php
KSH, We have a very small fleet where I am now. The biggest fleet I worked with was 140 trucks, a mixture of Cat 797 & Kom930E, the fleet moved 1.2 million tonnes of dirt a day. We always used to joke that was despite the management not because of it....................