Brian it is my understanding that Avgas does not have alcohol in it, and the auto fuel contains no lead so that it does increase valve seat wear when used in an engine that does not have hardened seats installed. This was a big problem in 1975 and on for all 1974 and older vehicles because they were set up for lead and head/valvetrain life was dramatically shortened. A simple fix was to have the heads pulled and 3 angle valve job performed and hardened seats installed at the same time. This was the only adjustment that had to made besides a small timing adjustment, since the overall octane did go down, so timing and later engine compression was reduced to compensate. Only when the use of EGR valves and computer controlled timing with knock sensors and the like was incorporated was the compression brought back up in later engines. If the O-300 does not have hardened seats then it will be necessary to either run 100LL periodically, or use a lead additive substitute to lubricate the valves, and prevent accelerated seat wear. If the timing has been adjusted properly for auto gas use, then no other consideration should be necessary.
Colin & Bev Rainey KR2(td) N96TA Sanford, FL crain...@cfl.rr.com http://kr-builder.org/Colin/index.html
