Depended on how good the filters and seals were. In automobile engines if the ash made it into the motor it pretty well killed it. Between the grinding action of the grit and the glass like beads that were produced in the combustion chamber, if the fine ash found it's way into the motor it was pretty much toast. On Geeps and F-units BN started coating carbody filters with oil to catch extra stuff, filters were changed more often. It probably increased the wear on the traction motor gears, but how much was anybodys guess. Traction motor blowers usually blow out from inside the unit, so ash would tend to be blown away. BN got on washing things down pretty fast, starting with the main lines and working towards the branch lines. Several local cabooses recieved sealant on the wood floors to keep the ash from seeping though between the boards, it helped, but the ash did find its way in. The impact depended on how heavy the ash was too, closer to the mountain the stuff was more coarse like sand, further away in Spokane it was like flour or powdered sugar. Farmers in eastern Washington added second air filters to tractors and trucks as added protection. The main way the ash found its way into a motor was through air, in fact most damage came from the stuff floating in the air which is why they wanted it washed down. The exception to the rule of washing down was with electric utilities, they were forced to use air to blow the ash off of the tops of transformers and substation equipment---fortunatly mother nature gave them some time to accomplish the task as it didn't rain for a couple of weeks----if the ash would have gotten wet it would have become a conductor and shorted stuff out all over the place. (Milwaukee electrification might have had some fun dealing with the stuff--had it still been around).