A loud bang or clunking sound when engaging first gear on a cold engine is not uncommon for some motorcycles, including Harley Davidsons. This phenomenon is often referred to as a "clunk" or "gear lash" noise. It occurs due to the slack or clearance in the drivetrain components, particularly the gears and clutch.
When the engine is cold, the oil is thicker, and the components may not be fully lubricated or warmed up. This can lead to increased noise and a more noticeable clunk when shifting gears, especially into first gear.
They can assess the condition of the clutch, transmission, and other relevant components to ensure everything is functioning properly.
Regular maintenance, including checking and changing the oil regularly, can help mitigate excessive noise and ensure smooth operation of the drivetrain. Additionally, following the manufacturer's recommended warm-up procedures and allowing the engine to reach operating temperature before engaging first gear can also help reduce the noise.