CCC 2185: On Sundays and other holy days of obligation, the faithful are to refrain from engaging in work or activities that hinder the worship owed to God, the joy proper to the Lord’s Day, the performance of the works of mercy, and the appropriate relaxation of mind and body. Family needs or important social service can legitimately excuse from the obligation of Sunday rest. The faithful should see to it that legitimate excuses do not lead to habits prejudicial to religion, family life, and health.
So, as Leopard says, as long as your bike-fixing doesn’t interfere with your Sunday obligation, go for it. Maybe you could listen to a CD of some religious music while you fix it.
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