Retiming the main drive (GR/FR)

Retiming the main drive (GR/FR)
Difficulty	Intermediate
Duration	15–45 minutes
For series
Tools	JIS phillips #2 screwdriver Needlenose pliers White paint pen/whiteout 1.5 mm hex wrench Flashlight

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One of the most common repairs on machines is retiming.

Timing, in this case, refers to the relationship between (1) the angle of the drum and (2) the position of a series of cams which operate the first and second paper feed. In the back of the riso are two large pulleys, each with cams and discs attached—during each print, both pulleys rotate exactly once. They are held "in time" (moving the same amount, at the same speed) by a long rubber toothed "timing belt." When a riso is out of time, it means one of the pulleys has rotated independent of the other, so that they no longer have the same angle.

Retiming the riso then, is the act of realigning the pulleys to once again match up.

Symptoms

Because timing controls two of the biggest systems on the riso (paper feed and drum/press/printing), when it is incorrect there are multiple symptoms which may emerge.

• A machine losing time is usually due to a drum getting stuck (fixing the drum pulley) while the main motor continues to turn (turning the paper feed pulley regardless). When this happens, the belt will click over the main motor pulley creating a very distinct loud ratchet sound.
• Print position slid off the edge of the sheet (usually to the left) on all prints is also a sign the machine is out of time.
  • Generally a print being off-center by more than 12 mm is a sign that the belt has skipped at least one tooth.
  • Note that prints being slid off the left edge of the page can also be caused by paper getting stuck for a cycle in the first paper feed, and feeding later than expected. So if it seems like the riso is only feeding sheets at half speed, on every other rotation, it's more likely this is a first paper feed issue. (In this case the sheet is fed early during the riso's attempt to feed another sheet.)
• If the machine is very out of time (more than a few teeth on the belt) it is likely that 'no paper will feed at all'—though many other issues with the paper feed system could cause all sheets to jam.

The true way to know if a machine is out of time is to manually check the position of the pulleys by opening the back of the riso. Turn off the riso, unplug it, and remove the plastic cover (5 screws). Then compare the positions of the two pulleys to the following.

• There is a small hole in the main drive cover at the 12:00 position above the drum pulley shaft—shining a light from above will show that this hole goes straight through a corresponding hole in pulley.
• On the paper feed pulley, there is a small hole in the pulley which should be roughly at 4:00 when looking behind the main drive cover from below.
• If the pressure disc is properly positioned on the drum pulley, it will have a small hole centered on the light interrupt sensor at the 9:00 position.
• If the p-disc is properly positioned on the paper feed pulley, it will have a small notch which aligns with a light interrupt sensor at the 3:00 position (centered on the sensor for B4/legal positions, or aligned with the bottom corner for A3/ledger machines).

Procedure

To retime the risograph, tension must be released on the main belt, then the paper feed pulley can be turned to the correct position relative to the drum pulley. Afterwards the belt will be retensioned, the position of all parts of the main drive checked, and then timing will be confirmed with a print test.

Setup and evaluation

1. Remove the drum from the risograph.
   • If the drum is still rotating freely, remove it as usual, using the green light-up button.
   • If the drum is stuck, turn the machine off and unplug it first, then manually remove the drum before proceeding.
2. Turn off and unplug the risograph.
3. Remove the back plastic cover (5 screws).
4. Check the position of the drum pulley—it should be in the "home position," with the hole at the 12:00 position lined up all the way through the pulley.

Drum free rotation

1. If the drum pulley is not aligned (the riso is not in "home position"), plug the riso back in and turn it on in test mode (holding down the L/P and M/P buttons while turning it on).
2. Close the front door.
3. On the main circuit board at the back of the machine, find a small push button labeled "SW1" or "DRUM FREE"—this is the free rotate button, when pressed, it will turn the main motor at 15 RPM (half the slowest printing speed), until released.

Use extreme caution whenever the riso is on and the mechanical components are exposed. Keep hands away from all mechanisms and moving parts. Pressing the wrong button inadvertently, or having the riso behave unexpectedly, can send very powerful motors and springs running, and there is a real risk of injury, particularly crushing of hands or fingers.

4. Shining a light at or above the 12:00 alignment hole on the drum pulley, cautiously (with hands away from all the mechanisms) press the drum free rotate button to rotate the main drive of the riso, until the hole in the pulley is aligned. (Tapping the button will allow very fine adjustment.)
5. Once the drum pulley is back in home position, turn the riso off again and unplug it.

5. Look at the paper feed pulley on the right to evaluate roughly how far the machine is out of time.
   • Use the small hole(s) on the main drive cover to evaluate if the hole in the pulley is at least near to them, or if it's not in the region.
   • If the alignment holes are close, skip to #Creating a test print.
   • If the alignment holes are not close, continue to #Releasing belt tension. (After making a coarse adjustment to get things close, creating a test print will allow fine-tuning.)

Detensioning the main drive belt

The belt is tensioned by the clutch assembly—detensioning it involves loosening the assembly and turning it away from the belt.

1. Attached to the top of the clutch assembly is the horizontal "timing spring"—the right side will be hooked into one of three slots. Note which slot it is in, then unhook that side of the spring.
2. Let the timing lever fall to the left with the spring.
3. Loosen the 3 screws in curved slots, at the back of the golden clutch assembly.
4. Turn the clutch assembly clockwise to release tension on the main belt.

Adjusting the timing

The timing is adjusted by rotating the paper feed pulley while the drum pulley remains stationary. To adjust the angle of the pulley, grasp it around the main drive cover, gripping it at 11:00 and 6:00, and moving it a little at a time beneath the loosened belt. The belt can also be shifted around the pulley to make small adjustments to which notches it is clicked into.

The procedure is slightly different for a coarse adjustment (the holes on the paper feed pulley were not closely aligned, and no test print was made) vs. a fine adjustment (the alignment holes on the paper feed pulley were close, and a test print was made).

Coarse adjustment

Fine adjustment

When making large changes to the position of the paper feed pulley, the drum pulley must first be locked into place. Using a 2 mm hex wrench, loosen the set screw in the pressure disc, on the end of the drum pulley shaft. This will allow the disc to spin, so that it is no longer blocking the 12:00 alignment hole. Once the alignment hole is free, put a screwdriver or hex wrench through it and the pulley—this will hold the drum pulley more or less in place while adjusting the paper feed pulley. Before turning the riso back on the screwdriver or hex wrench must be removed or there is a risk the riso may be damaged (and it will certainly lose time again). Rotate the paper feed pulley until the alignment holes at the 4:00 position are close to lining up. This will require a lot of shifting the belt around above the paper drive pulley, so that the belt doesn't get pulled with the pulley as its turning. Once it is aligned, remove the screwdriver/hex wrench that was securing the drum pulley. Rotate the pressure disc back into position on the drum pulley (small hole centered on the 9:00 sensor), hold it flush to the end of the shaft (suspending the disc between the two wings of the sensor), and use a 2 mm hex wrench to tighten the set screw in the disc.

It can be difficult to determine if very small changes have been successfully made, so the current position of the paper feed pulley should be marked relative to the pulley. Using a white paint pen or whiteout (or some other implement that can make visible marks on black rubber), mark a point on the pulley and a matching point on the belt (this is easiest right where the belt separates from the pulley beneath it, around 5:00). Reference the test print to determine which direction the paper feed pulley needs to turn and how many teeth (counterclockwise if the print is too far left, clockwise if too far right; one tooth per 12 mm offset). Check the marks made on the pulley and the belt to determine if the belt has actually changed position on the pulley (it is very easy to mistakenly rotate the whole system instead of adjusting the paper feed pulley independently). Managing the slack in the belt can be an easy way to turn the pulley one tooth at a time. When the belt is initially detensioned, the slack will be below the pulley. Shifting the belt up without rotating the pulley will allow the belt to be clicked back in one notch higher up, moving the pulley clockwise one tooth. Conversely, rotating the pulley counterclockwise slightly, and allowing it to turn the belt with it, will move the slack above the pulley. Then the belt can be shifted down without rotating the pulley will allow the belt to be clicked back in one notch lower down, moving the pulley counterclockwise one tooth.

Retensioning the main drive belt

After making the adjustment, the belt needs to be retensioned, the timing spring reset, and the pressure and p-discs checked for alignment.

1. Turn the clutch assembly counterclockwise to put tension back on the belt (this may cause some parts of the main drive to rotate slightly)—while holding it turned with some force, tighten the 3 screws at the base of the assembly (in the arc-shaped slots). Tighten each to hand tight, then give a small extra tighten to each.
2. Using a set of pliers (or spring puller, or other hook shaped tool) pull the timing spring back into the notch it was originally hooked into.
3. Check that the 12:00 alignment hole on the drum pulley is still aligned. If it is not, use the "Drum free rotation" instructions in the #Setup and evaluation section.
4. Check the position of the pressure disc on the drum pulley and p-disc on the paper feed pulley, referring to the diagram at the top of this page.
   • If either needs to be adjusted, use a 2 mm hex wrench to loosen the set screw in the collar of the disc, rotate it to the correct position, make sure it is flush with the end of the shaft, and tighten the set screw back down.
   • It's important that the disc is suspended between the two plastic wings of the sensor it passes through—if it contacts the sensor while rotating the sensor can break very easily.