Anyone have an opinion on the STC’d Interav alternator conversion for the older Musketeers?
I don’t have personal experience with an Interav conversion on a 1963 Musketeer. I do have some experience with them on other aircraft. I do not like their bracketry and regulator setup, and the alternator they use is not as robust (in my opinion) as the later alternators used by Beech and Lycoming. The alternator is a Wilson copy of the old Motorola alternator. In their defense, variations of this alternator are used on a wide variety of marine and heavy off-road equipment, and they have a slightly smaller profile than the later Prestolite/Ford alternator. Many versions of it are sold through NAPA auto parts stores.
One of the problems I have encountered is Interav furnishing the alternator with a cooling fan having the wrong rotation orientation. An alternator fan is supposed to suck air from the inside of the alternator and exhaust it from the perimeter of the fan; they operate on a centrifugal pump principal. Some alternator fans have straight blades; they will work in either direction, but are less effective than a fan designed with slanted blades for a specific rotation. When a slanted-blade auto-fan alternator is mounted on an aircraft engine, the fan turns the wrong way. It tries to pull air from its perimeter and push it into the middle of the alternator; airflow is cut by more than two thirds, and alternator failures result.
I have had problems with the Interav multi-piece mounting brackets breaking. They are difficult to keep tight, and are very susceptible to vibration.
Another problem has been with the regulator setup they provide. On the ones I have worked with, the regulator is in a package mounted on the outside of the alternator, with the control wiring going to the cockpit. The regulators fail due to the heat load in the compartment, partly from the alternator itself.
Some, all, or none of these factors may come into play in the STC’d kit for the Musketeer; I just don’t know. If you pursue the kit, if I were you I would talk with the manufacturer to get clarification on the nature of the kit contents for the application you are investigating.
Beech and Lycoming equipped the later planes with an alternator. Since the parts are standard Beech/Lycoming parts that were used in the same airframe, you should be able to install them on your plane with a logbook entry and an informational 337 to the FAA (as opposed to requesting a Field Approval). The key aspects are verifying fit, rounding up the needed parts (brackets, regulator, alternator), and locating a reliable mechanic (A&P-IA) to make the change and do the proper paperwork. I would exhaust the possibility of just upgrading to the later configuration before resorting to the Interav kit.