If your Heidelberg GTO 52 is dropping sheets, marking the gripper margin, or jamming at the delivery
\npile, the delivery grippers are the first place to look. On a GTO 52 the gripper bar carries the sheet
\nfrom the last printing unit around the delivery drum and releases it onto the pile. That single job
\ndepends on gripper springs, pads, the opening cam and the slow-down system all working together. When
\none of them wears, the symptom shows up downstream \u2014 as a pile jam, a torn leading edge or a printed
\nsheet with gripper bite marks. This guide covers how to diagnose worn delivery grippers and how to
\nreplace them properly.<\/p>\n
The delivery gripper bar rides on two delivery chains and is driven around the delivery drum. Each bar Everything in that sequence is mechanical and time-based. Gripper clamping force comes from springs; A GTO 52 delivery gripper bar is a small assembly, not a single part. Before you pull the bar out, have Stop the press, switch off the main drive, and lock out the power. The delivery chain is heavy and Bring the bar you intend to service to the lower front of the delivery, where you can reach both ends Slacken the delivery chain tensioner, then undo the gripper bar mounting bolts at both ends. Support On the bench, check each gripper for spring preload (all fingers should feel the same), pad wear, and Build the bar up on the bench: grippers, springs and pads first, then check that every finger closes Reinstall on the marked chain links, tighten the mounting bolts evenly, then restore chain tension to Turn the press over by hand and watch a gripper bar release a sheet at the pile. Release should be Run a few hundred waste sheets at production speed with the pile at working height. Check for bite Not every gripper fault needs new parts. Weak spring preload, a slightly late cam and a low pile can
\nholds a row of individual grippers that clamp the sheet by its leading edge as it leaves the last printing
\nunit. As the bar approaches the pile, an opening cam and pin<\/strong> lifts the gripper fingers so
\nthe sheet is released. At the same moment, the slow-down ring or slow-down band<\/strong> decelerates
\nthe sheet so it lands square and flat on the pile instead of slamming into the stops.<\/p>\n
\nrelease timing comes from the cam; landing quality comes from the slow-down system and the pile height
\nsetting. Wear in any one of them throws the others out of balance, which is why “the delivery is
\nmisfeeding” is rarely a single-part fault.<\/p>\nSymptoms of Worn GTO 52 Delivery Grippers<\/h2>\n
\n
\n gripper pads and weak springs let the sheet shift under the gripper during transfer.<\/li>\n
\n delays release, so sheets are pulled out of the pile or drag back into the delivery.<\/li>\n
\n slow-down ring or slow-down band problem rather than the grippers themselves.<\/li>\n
\n a damaged gripper finger, or a worn gripper pad that no longer spreads the load.<\/li>\n
\n gripper bushings, or excessive delivery chain slack.<\/li>\n
\n On a multi-bar chain this usually means the bars have been serviced at different times and now differ
\n in spring preload and pad wear.<\/li>\n<\/ul>\nParts Worth Having on the Bench<\/h2>\n
\nthe consumables ready:<\/p>\n\n
\n GTO52 delivery gripper complete
\n assembly<\/a>, which lets you build up a spare bar off the press and swap it in during a changeover rather
\n than during a run.<\/li>\n
\n the fatigue, and they are cheap compared with a press stoppage.<\/li>\n
\n gripper opening cam and pin<\/a> if release timing is inconsistent or the pin shows a flat spot.<\/li>\n
\n GTO\/MO slow-down ring<\/a> is the standard
\n consumable.<\/li>\nStep-by-Step Replacement<\/h2>\n
1. Isolate the press<\/h3>\n
\nunder tension \u2014 never work on a bar position that the main drive can index while you have hands in the
\ndelivery.<\/p>\n2. Index the chain to a comfortable working position<\/h3>\n
\nof the bar. Mark the bar and its chain position before removal so it goes back on the same links.<\/p>\n3. Release the chain tension and unbolt the bar<\/h3>\n
\nthe bar as the last bolt comes out \u2014 do not let it hang on one end. Lay it on a clean bench, gripper side
\nup.<\/p>\n4. Inspect before you replace<\/h3>\n
\nfree movement on its pivot. Check the bar for straightness, the backing plate for grooving, and the
\nopening cam and pin for flat spots. Replace the whole set if more than a couple of grippers are worn \u2014
\nmixed old and new grippers on one bar guarantee uneven sheet hold.<\/p>\n5. Fit the new grippers<\/h3>\n
\nand opens smoothly with no binding. Keep the assembly clean and dry \u2014 oil on gripper pads causes sheet
\nslip and marking.<\/p>\n6. Refit the bar and set the chain tension<\/h3>\n
\nthe value given in the GTO 52 service manual. A delivery chain that is too tight loads the sprockets; too
\nloose, and the gripper opening timing drifts.<\/p>\n7. Check gripper opening timing<\/h3>\n
\nprogressive and identical on every bar. If one bar releases late, the cam or pin is worn; if the whole
\ndelivery releases late, the opening station setting has drifted. Use the timing figures from the press
\nmanual \u2014 do not set this by eye.<\/p>\n8. Test run<\/h3>\n
\nmarks on the leading edge, sheets dragged back out of the pile, and square landing. Then re-check chain
\ntension and gripper bar bolt torque after the first run, since a new bar seats itself into the chain
\nrun.<\/p>\nAdjust or Replace?<\/h2>\n
\nall be adjusted. But when gripper pads are flattened, springs have taken a permanent set, or the opening
\ncam pin is worn through its hardening, adjustment only buys time \u2014 the press will drift back out of
\nspec within a few shifts. In a production shop the economical answer is usually a spare bar: build one
\nup with new grippers, keep it on the shelf, and swap it in so the press is down for minutes instead of
\nhours.<\/p>\n