Alternator longevity

We have a Motorola 60A alternator on our Glasair that S/H offered as an
option 20 years ago. Ostensibly a Heavy Duty model for police cruisers. Came
with larger pulley to reduce rotational speed, reverse fan for proper
cooling with Lyc engine. Still, I have to overhaul it every 400 to 500
hours.

In eleven years, have had to replace one case half (fretting at the bearing
cup), bearings (upgraded to HD bearings, but not much improvement - they
still start making noise at 500 hours), and this last time, the stator
failed from vibration. (It came loose in the housing and a wire broke.) Just
about every part has failed after 2600 hrs except the rotor. I'm paying
about $50 per overhaul, and have about $250 invested. Have a blast tube
blowing on the alternator for some cooling. The belt has always been fairly
loose, so as to not put excessive side loads on the bearing. Prop has been
balanced.

I never hear of my fellow homebuilders fixing their alternators. Am
wondering what kind of time between overhaul you with more than 1000 hours
are seeing on front mount alternators? What lasts the longest?

I'd switch to the Nippon everyone seems to use, but we have an old narrow
deck engine, and I have a funky, custom case mount bracket arrangement that
I'd rather not re-engineer if I don't have to. (That is, the wide deck uses
a standard boss mount bracket, that most of the after market alternators are
designed to fit. Not so easy for us.)

Thanks,

Mike Palmer

Info on Glasair gear bracket crack
www.members.cox.net/mp palmer (take out the space)