Short image . Magenta.

Speedmaster 102 SM 5+l.
Order of superimposing of colors KCMY. The first printing unit under pressure smoothes paper.
On the 4th printing unit (Magenta)the image is ≈0.15 mm shorter than on remaining. Printing plate CTP. Printing material from 65-300 grams. With a covering and without covering.Blanket normal. Plate normal.Elevations I checked everything normal. There corresponds the operation manual. In what the reason what to do?

 

You could distort the image with your rip via web growth and a few plate tests to nail it, but this does NOT resolve your problem.
A few things to look IMHO:

1.Check your impression dial indicator -if there is one unless there is CPC/CPtronic- and see when dial is set to 0 -and impression is on/thrown-, you should have a clearance of 0,35mm -use a feeler tongue- between bearers of blanket and impression.

2.Check your impression jacket for smashes -print a dry breakaway-

3.Measure blanket and impression cylinder

4.Make sure your blankets are tight with torque bar at same force

 

Does the magenta unit consistently print short? Do you have a packing gauge to measure your printing heights over or under the bearers? If the plate cylinders are packed to Heidelberg spec along with the blankets , then Id say you need to adjust the packings to make the magenta unit print longer. Are you familiar with the process of altering print length? If not do a search of the forum because im pretty sure I gave a detailed explanation on just how to adjust.

 

Everything that you have written, I have checked. There is the minimum deviation Magenta but all in the admission.

 

try removing .003" to .005" from under the plate. This may require you to completely remove the polyester permapack from the plate cylinder and replace it temporarily with regular blanket packing cut down to proper size. Use a micrometer to measure the thickness of the perma pack you removed, after completely cleaning the area you intend to measure. Make up paper packing to measure .004" LESS than the perm pack measurement. (if using mm you need to do the conversion!!!). Make sure your plate cylinder is clear of ALL adhesive from perma pack. Now this same .004" you removed from the circumference of the plate cylinder must be ADDED to the blanket cylinder in order to maintain the correct contact pressure. (this is assuming of course that your packings are right to start off with). At this point you will need to then set your impression cylinder pressure to .004 LESS than the other printing units. (again to compensate for the addition under the blanket). Once you've done all this Im betting you will see an improvement if fit. That .004" number can be adjusted up or down ,within reason, to dial it in to perfection. If you need to adjust it any more than .005" to .006" then id say there is something else wrong mechanically that should be looked at!!! Once your run a few jobs and dialed in your printing length, you can then purchase and install a new perma pack with the adjusted thickness to install on your plate cylinder. You must then remember to install the new packing amount under your blanket every time you change your blanket packing. Id suggest either you make up a sign near your packing drawers to remind you or to install or a little tag somewhere visible on that unit as a reminder. The last step would be to re calibrate the impression potentiometer to reflect these changes.
Good luck and let us know if it works for you.
If you should ever need to make an image print shorter than just do things I outlined in reverse. That would have you ADDING under the plate, subtracting under the blanket, and Adding to the impression.