Standby Generator Maintenance

I oversee buildings and grounds maintenance for a local Town and we have two large standby generators. I'm going to assume the maintenance of them as I saw the bill from an outside contractor to do the work and my department can do the same for more than 75% less cost. They are powered by large John Deere 6 cylinder turbos and do a test run cycle once a week, running for about 20 minutes.

My question is how often should these units be serviced if they don't have an extended run period...

Standby Generator Maintenance

Standby Generator Maintenance