Replacing a mainspring in a watch is just about the most common repair that I make each week. I thought I would give you a bit more information as to how this is done.

Here’s a Hamilton 992 with barrel cap off showing the break in the spring.

The spring will normally break at the center. That is where most of the stress is placed as it is wound and unwound.

This is the end of the mainspring. This Hamilton uses a “T” end spring. The two tips fit into the top and bottom holes in the barrel.

This is how the new spring is shipped from my supplier. In a “perfect world,” the spring is pushed into the empty mainspring barrel and the job is done.
This rarely works since I need to push the spring and have one of the ends perfectly hit the hole in the barrel.

When pushing it in fails then we will wind it in by hand. The spring is more than 12 inches long, very strong, and difficult to wind.
You will notice the nice “S” shape of the spring.

This is where years of practice comes in handy. I need to have one tip of the “T” end fit into the small hole in the barrel, wind it in without losing my grip which will send the barrel flying across the room!

New spring and barrel arbor in place.

Here’s a barrel cap back on. You will notice the small slot in the cap that matches up with the other end of the spring.
Sometimes the “T” end is a bit too wide, so you will notice that the last repair person has filed down the excess on the cap.
Mark Sirianni Watch Repair
25 Fraley Street
Kane, Pa. 16735
814-837-9435
814-558-4818 (cell)
watchdoctorpa@gmail.com

CHARLEY PHOTO OF THE WEEK: It’s getting cooler outside, so that means Charley is back sleeping on her bed in the workshop with all her pillows.

10 Comments
Gary
Mark,
You replaced a mainspring and serviced my Hamilton 992 watch a few years back. It’s nice to see pictures of how it’s done. I’m looking at that exact watch as I’m writing this. I wear it for a week or so each month. It still runs strong but does loose 20+/- seconds a week…. Not bad for a 99 year old watch from 1921. Thanks for your great work! Charley looks like I feel. A little tired right now.
Len. (UK)
I’ve wound a few main springs in by hand and it can be quite difficult.
Plus, of course, once yo get started, you cannot easily give up.
It’s as difficult to stop the ‘wind’ as it is to start it, because the intransigent spring takes no prisoners and, like a wild beast, released from captivity, it can do a lot of damage to anything that dares to get in its way.
Mark Morgan
Great information now I know why I go to a pro thank you.
Johnny
Thanks for explaining this Mark. You replaced a similar one for me several years ago.
Paul A. Baluch
Your blog is always informative and I love the Charlie pictures! Thanks Mark
Glenn Bevin
Thank you for the info. It makes me appreciate your hard work even more.
Charley is a delight!
Patrick Bissell
Good pocket watch article Mark. Love these, please do more. Give Charley a big hug from all of us.
Rick Campana
Mark
Like the rest of your readers, I’m so impressed by your patience and resolve when facing difficult repair challenges. It’s simply inspirational regardless of what profession one is in !
Michael Crestohl
In my opinion mainsprings can be dangerous if they get out of control. There’s a lot of power in one when it is wound tightly. M
Greg Keefer
Thanks Mark – interesting read. Charley looks very similar to my son and daughter-in-laws dog. She’s 7 years old.