I work at a Komatsu dealership. Komatsu and Cummins, as it was explained to me, goes like this, Komatsu uses engines that are bought from Cummins without a serial number. Komatsu then puts their serial number and engine model number on. Cummins will not acknowledge these numbers for any warranty or parts. Komatsu also uses engines that are their own build as well as ones that have a Cummins logo on them. It depends on what the machine model is. Komatsu has used everything from B series to l-10,m-11,855,n-14,qsk 19.
As far as the rest of the machinery line, pretty reliable machines on the whole, alot depends on how they are maintained, Remember though, if man made it, then man can sure as hell find a way to break it... ... .....
Very good product support and training from the factory. If you would like to become a heavy eqpt mech or something related to the heavy equip this is a good place to start