About 10 years after the introduction of GMC’s new inline six cylinder engine in 1939, General Motors issued a ‘Product Service Bulletin’ in regards to a recommended improvement on the 228, 248, and 270. It appears the manufacturer discovered a weakness that shortened the life of the engine timing gears. This recommendation was made for enlarging the oil supply hole leading to the meeting point of the two gears. The attached dealer bulletin was issued January 31, 1949.
This is especially interesting considering over a million GMC trucks with these engines had been built prior to this. The number includes the five years of military large trucks that were used during WWII under very abusive off road conditions!