Valjoux 7733 - chrono stops before minute jump

[Khan]

Hi

The chronograph stops when chronograph wheel touches the sliding gear to turn the minute recorder. I also noticed that the minute recorder is not smooth enough when turning manually while sitting in position. Attached is a picture without chronograph bridge for highlighting. The sliding gear alone turns freely. The problem existed before servicing as well. 

Edited April 29, 2020 by Khan

[Melt]

Never worked on one of these movements but if you remove the indexing spring from the minute record wheel does it still stop?

 

[nickelsilver]

A few things to check. On some chrono movements the hole in the mainplate for the lower pivot of the minute counter wheel is very close to the stem pivot, and a shock on the crown can distort the metal closing the hole slightly or allowing the stem to touch the counter pivot. Check that the minute counter wheel is very very free with the jumper spring removed. The hole in the mainplate can also simply be dirty, and as it is sort of buried in there is often overlooked for pegging.

 

When the finger on the chrono runner wheel comes in contact with a tooth on the sliding gear, it has to touch the flank of the tooth. If it touches tip to tip or even on the ogive, it can jam (if it's far enough along the ogive it's OK). You may need to adjust the depthing of the sliding gear, and/or shift the jumper to get the alignment right. With the chrono engaged a tooth on the sliding gear should be pointing at the center of the chrono runner. If you move the jumper you'll need to double check that the hammer is in full contact with the chrono runner heart cam and has a little play on the minute cam, while not pulling the minute wheel teeth to one side or the other of the jumper.

 

Don't oil the minute counter pivots.

[Khan]

Thanks very much for informative guiding. I figured out that, when the half moon shaped metal with a hole on the upper part of the min. Rec. Runner (marked red on image), is passing below the chrono bridge, the resistance occurs! And the top pivot goes off center as well. 

Edited April 30, 2020 by Khan

[Khan]

16 hours ago, Melt said:

Never worked on one of these movements but if you remove the indexing spring from the minute record wheel does it still stop?

 

Hi Melt

It runs in the same way no matter with or without the spring. It doesn't have an effect. 

[Khan]

After inspecting further, I believe that the chrono bridge hole for the minute rec. Wheel is too big as attached! That way, the wheel either get too loose or get stuck at the edge of chrono bridge hole. Am I right, that I need a new chrono bridge unless there is a way to repair/fix this? 

Edited April 30, 2020 by Khan

[nickelsilver]

It's kind of hard to see, but it does look a bit big. No need to change the bridge, that is a bushing and can be replaced with either a bushing or a jewel. What's puzzling is how it became enlarged, there is zero possibility that it happened through use. I have seen these where the bridge was screwed down with the pivot just outside the hole, and the pivot smashes the bushing closing the hole. Perhaps this happened and it was then broached a bit too much.

[Khan]

Thanks again:

Image 1 from before service and image 2 after service. I just don't have a jewelling tool, any one you can recommend from Cousins? They have the Horia in different versions. And how do You remove and fit a new bushing? Cant fint information anywhere on that. A new bridge would be the cheapest solution but a jewelling tool may be a good investment.