Chamberlain 3885C Attach the Rail to the Motor Unit, Set the Belt Tension, ASSEMBLY STEP, ASSEMBLY STEP

ASSEMBLY STEP 1

Attach the Rail to the Motor Unit

To avoid installation difficulties, do not run the garage door opener until instructed to do so.

•Remove the bolt and lock nut from the top of the motor unit.

•Place rail onto the bolt mounted on the motor unit and align the back hole with the hole in the top of the unit.

•Fasten rail with the washered bolt and lock nut previously removed. Tighten securely. Remember to use only these bolts/fasteners! Any other bolts/fasteners will cause serious damage to the opener.

•Cut tape from rail, belt and styrofoam.

•REMOVE STYROFOAM.

•Position belt over the motor unit sprocket.

CAUTION

To avoid SERIOUS damage to opener, ONLY use bolts/fasteners mounted in top of motor unit.

		Washered Bolt
	Lock Nut	5/16"-18x1/2"
USE ONLY THIS	Rail	Styrofoam
TYPE AND SIZE	Hole
BOLT

Motor unit

Sprocket

ASSEMBLY STEP 2

Set the Belt Tension

•	By hand, thread the spring trolley nut on the
	threaded shaft until it is finger tight against the
	trolley (Figure 1). Do not use any tools.				Trolley
•	Insert a screwdriver tip into one of the nut ring
					Threaded
	slots and brace it firmly against the trolley				Shaft
					Spring/Trolley Nut
	(Figure 2).
•	Place a 7/16" open end wrench on the square				Figure 1
	end. Rotate about 1/4 turn until the spring releases
	and snaps the nut ring against the trolley
	(Figure 3).				Trolley
This extends the spring for optimum belt tension.					Threaded
					Shaft
					Nut
					Ring
					Square
					End
	Trolley	Nut Ring	Trolley	Nut Ring
					Nut Ring
					Slots

BEFORE	AFTER RELEASE
1" (2.5 cm)		1-1/4" (3.18 cm)

Figure 2

Figure 3

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