Edelbrock 7890, 7891 user manual

Page 1

Brochure #63-0025

Rev. 1/03

ACCU-DRIVE CAM GEAR DRIVE SYSTEM

#7890 for Small Block Chevrolet V8s

262-400 c.i.d. 1957-1995

#7891 for Big-block Chevrolet V8s

396-454 c.i.d. 1965-1990

Installation Instructions

PLEASE study these instructions carefully before installing your new gear drive. If you have any questions or problems, do not hesitate to contact

our Technical Hotline at: (800) 416-8628 from 7:00 am to 5:00 pm, Monday through Friday, Pacific Standard Time or e-mail us at:

edelbrock@edelbrock.com.

• EMISSION CONTROL SYSTEMS: Check local laws for requirements. Not legal in California on pollution controlled motor vehicles. Not

recommended for computer-controlled vehicles equipped with knock sensors.

• POWER PACKAGE: Edelbrock Accu-Drive gear drives are part of a Total Power Package parts system that can be completed with the use of dynomatched Performer, Performer RPM, or Torker II cams, intake manifolds, and carburetors. For competition applications, use Edelbrock Victor or Victor Ram intake manifolds. Please refer to the Power Package Guide in the Edelbrock catalog to select all the components you need.

ACCU-DRIVE OPERATING PRINCIPAL

The Accu-Drive system utilizes a free floating idler gear that is self-aligning and connects the crankshaft and camshaft gears into proper mesh. The large power idler gear (SBC 21 Tooth/BBC 23 Tooth ) is positioned on the right side of the engine (passenger side). During normal operation, the drive power is transmitted from the crankshaft through the large power idler to the camshaft gear. During the running operation, there is no backlash between these gears. The small reverse idler gear (SBC 18 Tooth/ BBC 20 Tooth ) located opposite the large power idler gear, is also free floating. This small reverse idler gear does not carry any operating gear loading. The small reverse idler gear must be allowed to float vertically as noted in Figure 1. The small reverse idler gear prevents the large power idler from being disengaged from mesh in the event the engine is rotated backwards.

GEAR ASSEMBLY CAUTION NOTES

1. Never hammer directly on gears. You will damage the gear teeth and cause early failure.

2. Lubricate all gears and bearings with engine oil before installing front cover.

3. The small reverse idler must be free to float vertically with the large power idler in tight gear mesh with the crankshaft and camshaft gears. See Figure 1 for proper clearance. CAUTION: If gears do not have proper clearance the gear teeth will become overheated and discolored and will fail due to excessive friction between the mating gears.

4. Large power idler shaft length may require material removal to obtain the correct clearance between the cylinder block and front cover. See Figure

5. Torqued to 20 ft./lbs. You may also use Locktite™ or equivalent on bolt threads.

6. If a non-stock front cover is used be sure idler gear axles do not have more than .030" front end clearance. Install allen head capscrews into the front face of the cover if necessary to obtain proper clearance. Figure 3 & 4.

7. Do not use aluminum hub harmonic balancer with your Accu-Drive. Use only stock or aftermarket steel harmonic balancers.

INSTALLATION INSTRUCTIONS

NOTE: THE FOLLOWING STEPS ARE CRITICAL FOR THE PROPER OPERATION OF YOUR ACCU-DRIVE!

1. Remove stock timing cover. Rotate engine to Top Dead Center of cylinder #1 so that the timing marks on the original crank and cam sprockets are directly lined up with each other, i.e., the mark on the crank sprocket will be straight up and the mark on the cam sprocket will be straight down. Using suitable gear puller, remove stock crank and camshaft sprockets and timing chain. Refer to repair manual if necessary for individual steps.

2. Assemble Accu-Drive as shown in Figure 1

3. Install crank gear with the large chamfer toward rear of engine and timing mark toward front of engine. Make certain crankshaft drive key is aligned with keyway of the crank gear before assembling. Install the crankshaft gear on the crankshaft using the desired keyway. The rounded keyway

(●or “0”)

is for standard camshaft timing. The

triangle shaped keyway

(▲or “A”)

is for 4-degree camshaft advance

while the flat topped keyway

(■or “R”)

is for 4-degree camshaft

retard.

4. See Figure 2 “Camshaft gear assembly” for correct assembly.

(a) Place well lubricated thrust washer on the rear (block) side of

cam gear.

(b) Align the three bolt holes and timing hole of the cam and gear

and install the gear.

5. Align the cam gear and crank gear timing marks as shown in Figure 1.

6. Install the large power idler gear sub-assembly as follows:

(a) The large power idler gear must be installed on the passenger

side (right side) of the engine.

(b) With large power idler gear cranked tightly into mesh, make

certain the small idler (left side of engine) has free vertical movement (clearance) of no less than .005" or no more than .070".

NOTE: The gears will be severely damaged from friction if the small

idler does not have the proper running clearance as noted.

Page 2

Brochure #63-0025

Rev. 1/03

7 With the idler sub-assembly fully installed in mesh with crank and

cam gears and the large idler gear axle all the way back against the block, check the clearance between end of idler axles and front cover as follows: (a) Place a small amount of clay on the front end of both axles as

shown in Figure 3. (b) Install front cover with gasket in place and tighten cover bolts. (c) Remove cover and measure the thickness of the compressed

clay. It should be .005"-.030". (d) If axles are too long and are bottoming out between the block

and the front cover, you will need to grind off material from axles

as noted in Figure 3. (e) Note: Non-stock timing covers may require special allen-type

screws be installed into the face of the cover to obtain the

correct thrust adjust ment for proper idler shaft clearance.

8. With all gears correctly in mesh and timed, tighten the three camshaft capscrews to 20 ft./lbs. It would also be a good idea to use Locktite™ or equivalent on the bolt threads prior to final assembly.

9. Install the front thrust bearing assembly into the center hole of the camshaft gear. Make sure that the bolt heads of the cam gear bolts do not protrude farther than the nose of the thrust bearing; grind or file if necessary.

10. Lubricate all gears and bearings with engine oil.

11. Re-install the front cover.

12. Re-install all components removed in preparation for step 1.

Edelbrock Corporation

2700 California Street

Torrance, CA 90503

Toll-Free Tech Line: 1-800-416-8628

Tech email: edelbrock@edelbrock.com

Line up Timing Marks on Shaft centerline

Reverse idle (20 Teeth) should have between .005-.070 free vertical travel with power idler in hard mesh with cam and crank gears

Power idler (23 teeth)

Figure 1

Figure 4

CrankshaftCrankshaftCrankshaft

.015 -.060 Clearance

Stock Front Cover

Standard Inside Depth

Aluminum Front Cover

Inside Depth more Than

Stock

Aluminum Front Cover

Inside Depth Less Than

Stock

.015 -.060 Clearance

Block

Install Screw in Front Cover to Touch Idler Pins

Mill Recess in Front Cover

Brass Thrust Ring

Locking Plate

Cam

Block

Crankshaft

Cam Gear

Front Thrust Bearing Assembly

Capscrew

Timing Cover

Remove material from this end of axle.

Place clay in this area to check shaft end clearance

Figure 2

Figure 3

Timing

Mark