Quick update as I striped it down today.
I had very little idea what I was doing. I had managed to get my hands on a service manual for my movement (well two, as the manual for the model 27 that I have basically shows the day/date stuff then refers you to the model 24 manual). I was also lucky that an amateur watchie had done the same thing I was attempting to the exact same watch in a YouTube video, albeit sped up so fast you miss half the stuff, but it gave me some pointers and proved very helpful.
Many lessons were learned during the process.
The watch
A 1973 Timex - 26850 2773. Hand winding, but with day and date just to add complexity. Cost me the grand total of £16.91 off eBay (inc postage) and was running fast by ~10 minutes per hour.
Tools used
I bought:
A set of jewellers screwdrivers, basically 1.5mm and down, only really used one size but others performed non-screwdriver tasks
A set of precision tweezers, really only used one set
Automatic oiler pen
Toothpicks, not really needed
Had already/re-purposed
A camera lens blower (removed the brush)
Ice cube tray (to hold parts)
Chip extractor (from a computer repair toolkit, used in desperation to remove the hands)
The process
The hardest part was removing and re-attaching the hands -- they were a complete PITA to get off (I was pulling as hard as I dared). I hadn't purchased a hand removal tool, as I basically just bought the minimum I thought I could get away with. I didn't know if this would be something I'd attempt again so didn't want to waste too much money. A hand removal tool is probably worth the investment.
Separating the dial from the movement was another painful experience, partly because the Timex manual suggested you only need to remove the seconds hand. Having peeled back the tabs holding the dial to the movement I was worried I would do some damage to the dial because I was using so much force. Which is when I went heavy handed on the minute hand. I watched a video where the guy stuck a clear ziploc bag over the dial and plucked the hands off. That and my repurposed chip extractor just about did the job.
I was then able to lever the dial away from the movement and it brought the hour hand with it.
The rest came apart pretty easily.
Using some advice from another forum I skipped the pro cleaning fluids and covered it in lighter fluid (naptha, from the supermarket) then rinsed in pure isopropal alcohol (Amazon), before blowing dry (with the camera lens blower). I ended up doing this process twice as a couple of the hairspring coils still looked a little too glued together after the first pass. That may have been my imagination (too cheap to buy a loupe).
The Timex manual was decidedly lacking in detail about what to oil -- literally it says:
The movement should be re-oiled in the normal manner using only high grade watch oils.
Not a lot of use to a newbie -- the word pins was all I had to go on and some holes that appeared to contain the sharp end of what looked like a pin -- I added a drop of whatever oil came supplied in the pen I had bought -- the pen worked well -- prayed I'd got everything and started reassembling.
Again, the manuals are useless as they basically say "reverse the process" instead of any step-by-step or detailed diagrams. Even the video I'd found basically skipped reassembly. I put back what I had, it seemed to line up. I'll admit I was very skeptical just droping things back into place was enough.
The day and date wheels were fun as they basically fell apart when I lifted the dial off, so I didn't really see them in situ. Worked it out in the end.
I also had fun getting the stem back in as the spring for the notch mechanism was in the wrong place. Some patience and a few swear words sorted that. It went in and engaged, which was a good sign.
Getting the hands back on was easy enough, although hard to tell if I had them at the correct level. I didn't have a hand pusher to put them back on and I haven't managed to get the seconds hand reattached without catching on the minute hand yet -- largely due to me apparently bending the minute hand slightly when removing. I think I'll get there but another tool that may be worth the money.
A few turns of the stem and I waited with baited breath (there's always a delay as the power works through the mechanism). And then the seconds hand started moving! It's alive.
One minute later I was less impressed as the seconds hand got stuck on the minute hand. I've been round and round a few times, bending this and that, taking the seconds hand on and off. With it moving (I should find out how to unpower the watch really) it's not easy. So for now it's off.
Whole thing probably took me 3-4 hours (that £35 Timex service I found is looking a solid investment about now).
The result
I don't have a timegrapher, so I did a basic test of checking where the minute hand was, set a timer for one hour, check where the minute hand is when the timer goes off. Using that rudimentary test, it appears to be keeping good time. Certainly closer than 10 minutes per hour, but too early to say for certain.
The day window was out of alignment before too, and I have yet to see how that goes.
Will wait for it to run down and attack the hands again, see if I can finish it and then check for a longer period.
So a bona fide watch repairer now?
Baby steps. I happen to have a 25 jewel AS movement that's running very slow (another ill-advised, overly eager eBay purchase -- make sure to read the descriptions!), but I think that'll a bit more of a mountain to climb.
I might pick up the odd spares/repairs off the bay and dabble a bit more. Maybe work on something with some actual jewels.
Obviously I'm not advocating people rip the backs off their Rolexes and go at them, but you can achieve a fair amount with some patience and a simple set of tools. It's far less daunting a prospect having actually spent some time digging around in there. Mind you, not sure I'll be flipping non-runners any time soon.
I didn't think I did too bad though, considering I had barely a clue what I was doing, no prior experience and some forum posts and videos for guidance.