Venus 150 Chronograph Hammer Issues

[rodabod]

Hi,

I’m looking for advice from anyone who has decent experience with chronographs, and perhaps specifically the Venus 150. 
 

I’ve replaced a minute recording wheel on this Breitling as the pivot was broken where the hand attaches. Otherwise it was working ok. 
 

I’ve fitted the Cousins replacement and this appears to work well, except now the hammer does not strike the centre-seconds cam securely enough to stop any “slop” so the reset is inconsistently not zero. I’ve checked the seconds hand pipe is tight enough and can visibly see that the hammer is not pressing closely enough on the centre-seconds cam. 
 

I believe the new cam on the minute counter is slightly larger and is stopping the hammer reach the seconds cam properly. The new minute counter cam is 0.1mm wider. 
 

So... best approach or other ideas? I could buy a later centre-seconds runner so that it has a later cam, but that will be expensive. Or I could remove material from the hammer edge which hits the minute counter cam. The new minute counter cam is riveted on, unlike the original which is screwed on. 
 

Note that the photos are pre-cleaning and I do not believe this will affect the operation as the hammer itself has a good action and is being stopped by the minute counter’s cam. 

[spectre6000]

If it were me (and you're not, nor should you be), I think I'd take a file/emery stick to the top of the new cam. Original parts are only original once, but new parts can be sourced. You're forced into a new minute counter by nature of the repair, but the others are still original. That seems like the lowest impact and most cautious approach you could take. That said, I'm a dummy, and someone else will be along shortly to prove it.

[rodabod]

I believe the cams are glass-hard, so don’t think that would be a simple option. It would also potentially be difficult to maintain the original profile. 

[Watchtime]

Is it possible to change the staff and then use the old recording wheel?

[nickelsilver]

I frequently find that I need to file hammers on chronographs. You will want to check how the hammer is holding the minute counter wheel in relation to the minute counter jumper; it likely is pulling it one way or the other so the jumper isn't centered on two teeth. File the hammer face in a direction that will correct this, while introducing the freedom needed. Go very slowly, a little goes a long way- you don't want to start going back and forth between the hammer faces! When it's to the point that it is just making contact with the seconds cam, then you need to finish the hammer face. I do this with micron graded self adhesive abrasive paper stuck to a stiff slender steel backer, usually start with 20 or 12 micron, then down to 5, then 1. Ideally you want a mirror finish but as long as there aren't deep scratches "shiny" will do.

 

A tiny vice is a godsend for this kind of work, and I do it under a microscope.

[rodabod]

Superb. Detailed advice. Thank you very much. I tend to avoid chronographs, so this is very helpful. Cheers!