The tolerances for these parts is minimal even with a perfect mainplate, so it was no surprise that the reset hammer was dragging on the mainplate and the hour register was also binding. Rather than replacing the mainspring barrel when it was damaged, the previous watchmaker had tried to ‘work around’ the problem by bending the mainplate in several places to give the barrel more room – a big mistake!Īs you can see in the picture below, the chronograph hour register and its reset hammer are located on the dial side of the movement opposite the barrel, so consequently, bending the mainplate had an effect on these parts too. Further investigation revealed that the mainspring barrel had been damaged at some time in the past and was no longer running true – the teeth were visibly rising and falling as it rotated. On rebuilding the watch after cleaning, the wheel train was not running freely and had a noticeable tight spot. Having spotted that problem I thought that it would be plain sailing from here on in… but no. This drastically reduces the amplitude and causes a significant time gain. The whole movement was covered in a film of oil which had eventually found its way onto the hairspring, sticking two of the coils together. With the caseback removed, the cause was immediately obvious. Comparing the two movements you can see that the balance wheel is considerably smaller on the 726.Īlthough running on arrival, the watch was gaining around 5 minutes per hour, which immediately pointed to potential escapement problems. The higher beat rate increases accuracy, as a smaller, faster moving balance wheel is less affected by changes of position or knocks. The movement inside this watch is a Valjoux Calibre 726 which is derived from one of Valjoux’s most recognised and respected calibres, the Calibre 72.Ĭhanges were made the original Calibre 72 in 1974 to upgrade the escapement, namely decreasing the size of the balance and raising the beat rate from 18,000 to 21,600 bph. Another top quality vintage chronograph on the blog, this time from Eterna.
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