[Roger V]

While you're right about most roads being dirt, the majority didn't drive many miles back in the day. Somewhere I read that most people never left their county. So as Kevin said, Model A engines being very forgiving on injesting dust, very few miles being driven, and speeds/rpm relatively low, I could see engines lasting quite a few years. It's normal for us to be conditioned by what we do today. Our region/club drives a lot of miles as roads are paved but the downfall is most of it is done with higher rpm's then back in the day. As been said our driving today exposes the A to limited dust. Besides the potential gas-soaked filter most don't use a zero restricted K&N filter element and don't balance their carb so they likely have an over rich gas/air mix.