The Miyota caliber 8215 is a 21 jewel automatic movement, first introduced in 1977. It is made in Japan and is found in many new microbrand watches because it is easily obtainable, low cost, and considered an entry level workhorse movement.
Caliber 8215 VS 8205
There is a caliber 8205 which is virtually the same movement as the caliber 8215 but with an additional day complication next to the date.
Accuracy & Power Reserve
Miyota claims the caliber 8215 has an accuracy rating of -20 ~ +40 seconds per day. This is only measured within 10 to 60 minutes from a full power reserve. To achieve full power reserve, hand-wind the crown 40 times. Power reserve or fully wound running time is about 42 hours.
Time and Calendar Setting
You can hand wind the movement while the crown is in position 0. Pull the crown out one click to position 1 to set the time. Pull the crown out again to position 2 to set the date. Do not set the date while the time is between 9:00pm and 1:00am.
Hesitating second hand?
Back in the year 2000, Rob Berkavicius (Rob B on TZ) and Paul Delury (Gumby on TZ) wrote this article addressing the concern of the second hand momentarily stopping when the watch is bumped on the side. The team set out to explore why it happens on the caliber 8215, whether it is acceptable, and if it affected timekeeping. It’s recommended that you check out the entire post here, but the main idea is:
The Miyota cal 8215 is an indirect sweep seconds design, very common in Swiss watches of even very high grades in the past. It allows for an elegantly simple design of the the watch, in this case the top plate encompasses both the time and winding trains. This view of the train, shows the sweep second pinion which passes through the center wheel, and is driven by the 3rd wheel.
…The brake spring, while effective at removing jitter, does not provide enough tension to hold the pinion steady under all conditions. So, when the watch is knocked, the pinion may be moved partially or all the way to the other side of the “slop”, and it may take a second or so for the movement to “catch up” again. Although this looks cosmetically unappealling, it makes no difference at all to the timekeeping of the watch. Increasing the tension of the brake spring must be done with great care, as too much tension will start to significantly affect the balance amplitude (from the extra friction in the train), and thus the timekeeping. And, this indeed is one of the reasons why “direct seconds” watch designs are now favored by watch manufacturers.
The “Hesitating Second Hand”, observed on Invicta and other brands of watches is simply a characteristic of the “Indirect Seconds” type of movement design and in no way has any effect on the watch accuracy or timekeeping. If any watch company wanted to do something about it, the simplest, and really the only practical solution, would be to poise the second-hand. However, tens of millions of Indirect Seconds type watches of many different manufacture, in all grades from the cheapest pin pallet to high grade Swiss watches have been made in the past 50 years or so, and have been used with no problems at all. Indeed, it is hard to imagine how this characteristic could ever be observed during normal wear on the wrist, anyway. One can only assume it was claimed as a problem in an attempt to find fault in a watch which offers such excellent value for money as the Invictas do. So all you owners of Invictas, Omegas or any of the many, many other brands that use the same method for driving the second hand, there’s no need to worry about it!
Replacement prices were found online in the $40-50 range for individual movements. When ordering wholesale, the caliber 8215 comes in packages of 300. They are available with a higher quality “fine finishing.” Although the plastic movement holder (part 500-710) is more common in affordable watches, this is interchangeable with a metal ring (502-008).
Click here to buy a replacement Miyota 8215 movement for your watch.