C1085 duplex registration issue after 15 sheets

[dagoof]

Got a strange one on a c1085 - the image is slipping out of registration predominantly on the trailing edge (both sides) when duplexing. It happens almost bang on after 15 sheets give or take, never an issue with the first dozen or so. If I run batches of 15 sheets it's fine, with only a few seconds in between batches.
It doesn't happen when running simplex. Sporadically the issue doesn't happen at all (perhaps when the machine's been running for several hours).

Anyone got any thoughts? Spoke to some who said they didn't think the registration roller would be a factor but I'm not sure

[dagoof]

Anyone care to throw their hat in on this? Still got me stumped!

[Toxic]

Are you tech or end user?
Did you try something before to solve that problem?

[tsbservice]

Of course he is a tech with that nice little badge Still learning...
Imho every reliable tech should anchor on that motto.

@dagoof, will upload some docs in few minutes, check your PM.
Please, bear in mind I'm not a production guy, so articles may be somewhat or completely irrelevant.

[methogod]

what's the meter?
stock?

which way is it shifting?

[dagoof]

Big thanks to Tsb

Methogod - The machine's got a fairly high meter (6m). This was using a 300gsm silk stock.
The CMYK was slipping out of registration horizontally in the direction of travel (leading to trailing), I'll try getting a couple of pics.

[methogod]

would think registration assy, at 6m. was it replaced at all?

[dagoof]

Hi Methogod, we replaced the whole reg assembly but it's not really helped (it now pulls the reg back after slippage but will continue to fall out of registration on a cycle of 10-15 sheets).

What would you suggest next?

[BOTOY]

Hi,
I think this is no a mechanical issue. Can you reset the machine in factory setting, then make un new print/side setting?
Could you take some picture?

[Synthohol]

does it behave if regular 75-80 gm2 paper is used?
does the tray being used matter?
have you tried the paper through the bypass (if installed or accessible)
jig the door interlocks and watch the edge of the paper as it passes and look for drift.
if drifting check for even tension on every hard roller(s) in the paper path.