1. To install the NB-4120-2 Single Belt refer to NB-4120-2M3.
2. Install the (2)Right Door Attachments (lower belt) as indicated on drawing NB-4120-2P2. Do
not install the Left Door Attachment (upper belt) at this time. Assure the belt centerlines of the
brackets are parallel with the track centerlines (shim as required) within (+/-) 1/16” over track length.
3. Before mounting the Take-Up Frame, use a string or the timing belt to check the belt centerline
from the door attachments to each pulley centerline on the Take-Up Frame. Minor adjustment can
be made by loosening the shaft collars and moving the take-up shaft from side to side. Install
Take-Up Frame as shown on NB-4120-2M3 and NB-4120-2C3.
4. Before mounting the Gear Motor Bracket, use a string or the timing belt to check the belt centerline
from the door attachments to each pulley centerline on the Gear Motor Bracket. Minor adjustment
can be made by loosening the shaft collars and moving the Gear Motor shaft from side to side.
Install the Gear Motor Bracket as shown on drawings NB-4120-2M3 and NB-4120-2E2.
5. Verify the Take-up End Pulleys are adjusted in the direction toward the Gear Motor Pulleys as
much as possible by backing off the threaded rod.
6. Assure both doors are in the closed position before attaching the side of the H x 2.0” timing belt
marked “Take-Up Side/Right Door”to the Right Door Attachment (lower belt) closest to the
take-up side. Secure the belt with (1) of the Clamp Plates and the mounting hardware supplied per
NB-4120-2P2, making sure to tighten the (4) mounting bolts with an alternating sequence in order
to equalize the clamping pressure.
7. Taking out the slack, pull the Take-Up Side of the belt around the Take-Up Pulley and work toward
the Gear Motor End. Use a C-clamp to temporarily secure the belt to the Take-Up Pulley.
8. Pull the belt around the Gear Motor Pulley taking out all the slack. Use another C-Clamp to
temporarily secure the belt to the Gear Motor Pulley.
9. Attach the other side of the H x 2.0” timing belt marked “Gear Motor Side/Right Door”to the
Right Door Attachment (lower belt) closest to the Gear Motor End. Secure the belt as described
in Step 7.
10. Remove the C-clamps attached to the Take-Up Pulley and Gear Motor Pulley.
11. Assure the belt teeth are fully engaged into their respective pulleys. Adjust the take-up end
threaded rods as required. Adjust the Gear Motor End by shimming (shim pack included) the
bracket at the mounting surface.
12. Pre-Tension the belt enough to move the Right Side door to the open position by tightening the
take-up end adjusting rods in an alternating fashion.
13. Move the Right Side Door to the open position manually by using a chain wrench on the shaft
collars. (a wrench with sufficient leverage is required) on the Gear Motor Output shaft. If you prefer
to move the door to the open position under power at very low speed, skip to step 17 then go back
to step 14.
14. After the door has been moved to the full open position, the timing belt can be adjusted for full Pre-
Tension. The correct Pre-Tension in the belt has been set when measuring the force (F) to deflect
the belt 1.0” at mid-span per the formula in Parameters Section.
15. After moving both doors back to the closed position, install the Left Door Attachment (upper belt)
per drawing NB-4120-2P2. Assure the Clamping Plate is engaged into belt teeth and bolted to Left
Door Attachment, prior to securing to the Left Door.
16. While the Belt Idler has been pre-set to tension the slack side of the Gear Motor Pulley at the
factory, it is recommended that the Pre-Tension on the Belt Idler be checked by the same method
as in Step 14 and adjusted if required.
17. Caution: To prevent risk of serious injury, assure the source voltage has been disconnected and all
required lockouts have been activated prior to electrical hookup.
18. Caution: Hookup 230 VAC 3-phase supply voltage and grounding per Terminal Strip Hookup the
applicable Wiring Diagram and/or local codes. .