With a few exceptions you cannot swap one movement in lieu of another. There are too many parameters that have to match:

• Diameter
• Position (height) of winding stem
• Position of dial feet
• Hole diameters of hands
• Distance between movement center an dial ring
• Distance between movement center and second hand (for small seconds only)

 

How a mechanical watch works

In general, it is not practical to change a watch's movement to a different type of movement unless the two movements were designed to be interchangeable. To be interchangeable, the two movements must have the same

• diameter
• height
• stem height (distance from bottom of dial to the stem's axis)
• positioning of holes for dial feet
• diameter of holes for dial feet
• diameter of post for hour hand
• diameter of post for minute hand
• diameter of post for seconds hand
• positioning of seconds hand (e.g. central vs small seconds)
• positioning of date window (if date complication is supported)
• positioning of day window (if day complication is supported)
• positioning of case clamps (if used)

It is sometimes possible to replace a movement by a movement that is not fully interchangeable, but is nearly interchangeable. For example, an NH38A no-date movement can be replaced by an NH35A or NH36A at the cost of creating what is called a "phantom date" position between the winding and time-setting positions of the crown. As another example, an ETA 2824 automatic movement can be replaced by an ETA 2804 hand-wound movement, at the cost of creating some empty space between the movement and case back, which might require some change in how the movement is secured within the case.

 

Wanting a new movement is a great excuse to buy a new watch! [emoji14]

 

Not your definitive answer, but I have found this popular database to be very helpful when comparing watch hand sizes, movement dimensions, etc.

bidfun-db Archive: Watch Movements

www.ranfft.de

Regards
Joe


Sent from my iPhone using Tapatalk

 

Adding to what others have said...

Some movements were meant to be interchangeable, by way of having identical dimensions, if not designs. Sellita and a few Chinese factories make clones of the ETA 2824-2. The LJP G100 is also a dimensional clone. I believe the Soprod M100 is a dimensional clone of the ETA 2892-2.

When you start veering away from movements with identical dimensions, it is possible to do, sometimes, with a little ingenuity. I've seen guys add dial spacers to correct for differences in stem height or hands post height, or 3D print movement spacers to use within the case.

The 8215 and NH35 are both thicker movements than the 9015, so while the thinner 9015 may fit within the thicker case made for either of those two movements, that's not a guarantee all the dimensions will be conducive to a movement swap.

I'm fairly sure the dial made for the NH35 will not work with the 9015 (different dial feet locations and date window position), and their stem heights are different. Not sure about the 8215 vs 9015.

 

For the most part part no movements are not drop in compatible for all the physical parameters mentioned previously.
Clone movements would be the exception to this. ETA 6497/98 => Sea-gull S3600, Miyota 8215/05 => DG2813