Ok, here we go. When I print a 2 or more color job on my GTOZ there is a difference in registration between the first and the second color. The difference is parallel to the paper travel and by experience I can say it is the paper spreading by the pressure and the water. The funny thing is that I do not have exceeding pressure settings, nor lots of water and on my older GTO 46 single color press the registration always goes perfect. I have the blanket underpackings perfectly by the book, so should I change them? And which way?

Not sure if this helps, but I've had similar issues in the past. Do you have a direct to plate system? Pre-Press systems are not always our best friend. Check Grippers on Transfer Cylinders.

No, I'm sure the prepress is not an issue here, but I will check the transfer cylinders though I dont believe it's that kind of matter. The paper seems to be spreading rather than changing position as it would in such a case. So the question remains.

Does the image "grow" equal lateral and vertical? if yes, your paper is growing. That can happen even though you're using little water(because any paper exposed to more than 35% of room humidity can and will grow)

Is image growing more vertically than lateral? Try reducing blanket packing in the unit that is getting bigger (that will "shorten" the image) Even when you pack both units the same, blankets can vary in widht and therefore change the image size. For that purpose we bought a packing gauge. You can get it on ebay for 400 or 500 US.

I've done that in a SORMZ and worked very well. Just got a GTOz and will see if my advice works. Remember that the book works great with a new machine. Packing older machines can need a little bit more than the book.

Hope that helps!

Thank you for your replys. It is true that the packings should be changed by experimentation. It is time to change a the first unit blanket so I will also change the packing. I will let you know of the results.