2893-2 with wrong gear ratios??!!

[Champ22]

So I have two of the ETA2893-2 movements. One I harvested from a Bulova c869881. And one that I bought "factory new" from those kind Swiss people on Ebay that sell all sorts of Swiss watch parts.

Here is the baffling thing. On the "factory new" version, the 24h wheel lags behind the date indicator drive wheel. Because these both make one full rotation per 24 hour period, they should move identically. And they DO on the movement that I pulled from the Bulova. But on the other one they DO NOT turn at the same rate. For every full turn of the date indicator drive wheel the 24h hand wheel ends up about 1.25 hours short. Or, to put it another way, the date will change at a different time each day until, after 15 days, the date indicator will be 1 full day off. 

Now I know from mechanics that gear ratios are fixed. Which is why I cannot even imagine where the fault is with this movement. Nothing is slipping. And, like I mentioned, it's a brand new movement. 

Any ideas on where to look for the cause of this? (BTW, I've already done a full tear down and service of the one pulled from the Bulova. So complete disassembly won't be a problem if that is what is needed.) Thanks!

[Marc]

Just a thought, is the Bulova a GMT complication, but the other a moon phase complication? Not even sure if that would result in the miss-match that you are seeing but it may do.

[HSL]

The 2893-2 is actually a 2892-2 which is slightly rebuild with a new setup of gears.
The hour indicator driving wheel together with the universal hour indicator are the parts that makes you get the GMT 24-hour indication. So, it is not a pure 24-Hour drive.

Otherwise for the date part it is the original setup of gears that will interact.
The watch itself work with a 12-hour setup which is geared as usual.
You got the minute wheel driving the ordinary hour wheel, the hour wheel drives the intermediate date wheel, the intermediate date wheel is driving the date indicator driving wheel.

In a genuine movement it is quite hard to alter the gear ratios since it will affect the diameter of the wheels. The diameter difference will be easy to spot or even make the wheel train go so heavy the movement will stop.

If this “factory new” movement is missing a day after 15 days I would suggest the date indicator is not turning correctly and is skipping a date change, either from bad lubrication causing the finger on the date indicator driving wheel to slip.

If you bought it as a factory new movement you should return the movement to those Swiss people at Ebay that sells all kinds of Swiss watch parts .

[Champ22]

I figured it out.

The Intermediate Date Wheel was not seated properly. Instead of engaging with the bottom set of teeth of the hour wheel it was engaging the top set of teeth. Turns out these are different ratios. The two different sets of teeth on the hour wheel are different but close enough that they can both engage the Intermediate Date Wheel. And that's why the timing of the date change wasn't happening at exactly 24 hour intervals.

Thanks for the input everyone. I appreciate it!