This Lorenz chronograph was a recent arrival in need of it’s worn winding pinion sorting out along with a movement service. Powered by the Lemania calibre 5100 movement it’s a handsome looking watch. I’ve written about the calibre 5100 before so I’ll skip the history and just say it’s a very robust movement and because of this was used to power a lot of military (and military influenced) watches.

The caseback has the Lorez logo in the centre.

With the back removed you can see the typical 5100 architecture with the grey plastic spacers visible under the oscillating weight.

The first thing I noticed was the bush was worn on the weight, a common problem with the 5100.

With the movement out the dial and handset looks in great shape.

Once they are removed the strip down starts in earnest.

Note the abundant use of plastic in the construction. The oldest calibre 5100’s are over 40 years old now so the initial fears about the longevity of plastic parts can be discounted as they are proving to be extremely hard wearing. It’s not actually plastic but Polyoxymethylene or to use the trade name the developer (DuPont) gave it Delrin, an engineering thermoplastic used in precision parts requiring high stiffness, low friction and excellent dimensional stability.

Once I reached this stage it all went in the cleaning machine apart from the plastic parts as the chemicals in the cleaning and rinsing fluids have a tendency of turning the clear plastic plate slightly milky. The plastic parts are cleaned by hand.

The reassembly started without the new mainspring that hadn’t yet arrived. One of the nice touches with the 5100 is the fact the mainspring barrel can be removed without dismantling the movement by withdrawing it’s removable axle. The only other new parts needed were the winding pinion and clutch along with the oscillating weights bearing.

The above picture was as far as I could go with the reassembly before I needed to fit the mainspring, luckily it arrived in the nick of time 🙂

The hands and dial are refitted here.

The new oscillating weight bearing is fitted before the weight is re-attached.

With the watch re-assembled I though that was it but testing threw up an unintended consequence of the winding mechanism working again. When I gave it the final inspection after four days of testing I wound it manually, felt a click and it wouldn’t wind any more! What had happened was the strain of winding had broken the clutch inside the screw down crown which meant it needed a replacement sourcing and fitting.

Unsurprisingly I couldn’t source an original Lorenz crown but I managed to get one which was a good match. I also had to replace the stem as the original had a tap 10 thread and the replacement was tap 9.

It looked the part when fitted and was actually easier to grip than the old one so a sort of result I’d say! I’d also say it’s a very handsome watch 🙂