WHBM
Let me give you some experiences from the time of Mount St Helens in the USA, from those who were right alongside, and in comparison to which this Iceland volcano is a mere pimple in comparison.
Roads downwind were so extensively covered that they had to get snowploughs out; quite some damage was done by trees being overwhelmed by the weight of ash deposited o them, and they fell over.
Yet damage to reciprocating engines of various types was really non-existent. Railway locomotives on lines downwind were fine and carried on, provided they changed the air flters every day, cars were similar. I don't recall any increase in mechanical problems after the ash, although there was a lot of cleaning. Don't know about GA in the area but certainly airline service in the downwind area was little affected. And this was ash you could see.
This may be so for land-based vehicles but as far as I know, an aircraft does not have a designated air filter similar to a land-based machine.
Mike