Most inking-unit problems on a Heidelberg SM 74 do not start in the ink duct, the roller train, or the dampening system. They start in a bearing nobody looks at — a small part behind the oscillating inker that loses preload over a few hundred thousand impressions and quietly takes your ink density with it.<\/p>\n
By the time the symptom shows up on the sheet — tonal drift across the sheet, a band of starvation at one edge, ghosting that comes and goes — the bearing has usually been degrading for weeks. What follows is the preventive schedule we recommend for inker bearings on SM 74 and SM 52 presses: what to check, how often, what a worn bearing actually sounds and feels like, and the point where replacement is cheaper than another week of chasing colour.<\/p>\n
Rollers announce themselves. They glaze, they swell, they pick up, they leave streaks you can see. Bearings do not. They are loaded in a way that hides wear: the oscillating inkers on an SM 74 run a short stroke at high frequency, so a few microns of play turns into impact loading dozens of times per second. Once that starts, the failure accelerates — play increases, the roller axis wanders, contact pressure against the neighbouring roller changes, and the ink film stops being uniform.<\/p>\n
Four things kill inker bearings on these presses:<\/p>\n
Not every bearing in the inking unit is a wear item, but three of them account for most of the density complaints we hear from pressrooms:<\/p>\n
The SM 74 ink transfer bearing<\/a> carries the rotation of the ink transfer roller — the roller that meters the film coming out of the duct side. It is the first bearing to see a contaminated film when wash-up is sloppy, and the first to show up as uneven density from duct side to gear side. Our reference for this part is 00.520.0765; confirm it against your own parts book before ordering, because Heidelberg revised inker hardware across SM 74 production years.<\/p>\nOscillating inker axial bearing<\/h3>\n