Movements

The Miyota 8315 Movement 

Currently used in the Aurèn Ocean Dive Watch, the Miyota 8315 Caliber is a Japanese-made, automatic watch movement. Its reputation is built on three things: reliability, simplicity, and cost efficiency.

Movement Spec Summary

Automatic Winding System

One of the most distinctive characteristics of the 8315 is its Uni-Directional Rotor.

The rotor only winds the mainspring in one direction. When spinning in the opposite direction:

• The rotor freewheels
• Minimal resistance is felt
• Rotor momentum can become noticeable for a short period of time
  

Power Train and Mainspring

The movement stores approximately 60 hours of power reserve when fully wound.

This is achieved through:

• Traditional mainspring architecture
• Moderate beat rate (3 Hz)
• Efficient gear train
  
  

Manual Winding Capability

Unlike many inexpensive automatic movements from previous decades, the 8315 supports Hand Winding.

Turning the crown directly tensions the mainspring.

Benefits include:

• Easy startup after storage
• Less dependence on wrist motion
• Faster achievement of full power reserve

This feature significantly improves everyday usability compared with older non-hand-winding automatics.

Jewel System

The movement contains 21 synthetic ruby jewels.

These are placed at high-friction pivot points throughout:

• Gear train
• Escape wheel
• Balance assembly
• Rotor system

The jewels reduce:

• Friction
• Wear
• Lubricant degradation

Twenty-one jewels is sufficient for the movement’s architecture; additional jewels would not necessarily improve accuracy.  

Shock Protection

The 8315 uses Miyota’s Parashock System. The Parashock system functions similarly to other shock-protection systems by allowing limited movement of the balance staff during impacts.

Benefits include:

• Improved durability
• Reduced risk of broken balance pivots
• Better survivability during accidental drops

This contributes significantly to the movement’s reputation as a rugged workhorse.  

Serviceability

• Large global parts supply
• Simple construction
• Easy disassembly
• Inexpensive replacement movements
  

Major Upgrades Over Older Miyota 8-Series

• Hacking Seconds: Unlike basic older versions, pulling the crown fully out completely stops the second hand for precise time-setting.
  
• No Second-Hand Stutter: Features a direct-drive system that eliminates the visual "stutter" or lag sometimes seen in the older 8215.