You can repair ANYTHING in Halo Wars

• Using Spirit of Fire’s Heal and Repair is useful.  Just don’t use it in combat.  It only works when a damaged unit is NOT being attacked.
• Or you can heal the Transports if their health is low.  Press Up on the D pad to acess the leader powers.  The “Heal & Repair” option is available to repair.

Use this option to get the achievement: Repair the Spirit Of Fire’s power core in under 4 minutes