EB8800/8805 calendar spring tension or lubrication?

[mbwatch]

This week I've been trying to finish up what seemed very straightforward on an EB8800 or 8805 pin lever movement with a calendar date. I believe it was reliably changing date before I disassembled and cleaned it but on reassembly I am finding it changes 2 or 3 days before getting stuck where it advances the date ring about 80% but not quite enough for the detent spring to settle into the next position. It then fails to move forward. This movement has an instant changing date with an L shaped spring which is drawn back to the next date position's tooth (like the hammer on a revolver) and when a pear shaped piece under the date wheel  advances past the L shaped spring's hook, the spring should snap forward and push the date ring ahead, with the lower detent spring settling in between teeth.

I have been experimenting with spring tension and lubrication on it but would like your advice on whether I have taken the right action. It seems like I have it working now, but I'd appreciate a push if I went about this incorrectly.

First, here see what I'm calling the detent spring sitting not quite in the tooth on the date's 9. This was its failing state.

 

Here are the L shaped spring that pushes the date ring ahead, and the detent spring (underside) and the whole part:

 

After trying a few different lubrication methods on the springs where they contact the date ring I wasn't having any success getting it to move reliably. What did work was to gently bend the detent spring inward, reducing its tension so the date ring slides fully past and it settles between teeth.

I cannot find an oil chart for the EB8800 series and my experience with lubrication on date movements is mostly limited to Timex (which expect a grease like 9501 on the springs and a couple places where the inner toothed edge of the date ring contacts the metal dial plate.

To my questions, I felt like my options on fixing this were

1) Bend the L shaped spring outward, giving it more force when pushing the date ring forward. But this might have prevented it from pulling back far enough to engage the next tooth in its "cocked" position

2) Bend the detent spring inward to reduce its tension - this is what I did and it seems to work

3) Some combination of bending both?

4) Lubrication - 9501 or maybe HP1300 on the tips of the springs where they contact the date wheel, maybe also a TINY bit on the very edges of this cover plate, the small lip against which the date ring rides. I did not think it would help to oil the underside of the date ring itself with 1300.

In a lot of older forum posts, I am generally finding advice against lubricating calendar works but bending the spring seems to have been helpful. If you were working on this movement, would you have lubed the calendar? Would you have meddled with the springs, or have I been going about this wrong?

Thanks as always for your experience & help.

[mbwatch]

Update: The calendar is still changing reliably 3 weeks after bending that detent spring to reduce its tension so I am going to call this success.

[mbwatch]

A year later, another EB8800 and exactly the same issues with the calendar. It was again non-runner but the calendar worked perfectly before I attempted service. I went back to my own thread here to find out how I solved it last time and tried the same thing, bending that lower capturing spring up to loosen it. This did not have the right effect this time, and the calendar would catch and fail to advance on a few specific days.

I spent a bunch of time troubleshooting it, loosely greasing the calendar ring teeth, examining the contact points for the dates that were sticking most and not getting any positive changes. I remembered I had an 8800 junk movement and found its calendar would advance so I dropped those parts into the one I was working on, totally dry. It worked perfectly.

Rather than spring tension or grease where the calendar ring interacts with the springs, my mistake was that I had put a tiny bit of oil between the calendar driving wheel and the steel snail that sits underneath it, assuming it was needed for this metal on metal interaction and to help stick them together for alignment during installation. The snail is high polished while the calendar driving wheel is thin brass. The HP1300 oil was adding just enough drag to the snapping action when the snail advances that the calendar lacked momentum to advance past the detent spring. Reinstalling the driving wheel and snail dry solved it perfectly.

Edited February 25, 2024 by mbwatch