The 793380 camshaft is definitely a poor design. If Briggs would beef up ACR weight arm pivot area or redesign to a different ACR it solve the problem. As for failing I have seen them to fail on relative new engines ie low hours. I got one here that only had about 30 hrs on it that ACR broke. Under warranty when it failed but customer dragged around for several months before getting into shop and his warranty had expired.
When these fails most customer assume it is a starter problem and buy a non-returnable starter. When customer come in looking for a starter I ask several questions and if I suspect and ACR problem I suggest them to bring in the mower. Most time time it is just valve adjustment but every once a while it is the camshaft.
They so prone to fail, I see several a year, that I keep one on hand at all times for the sake of speedy repairs during the busy season. It is same with the head gaskets. Just a few years ago it was taking me a week to get these parts but I was lucky that one supplier started selling the Briggs parts that has a 2 day delivery window straight out a Briggs warehouse.
