Edelbrock 7891 - Manual

Page 1

©

2003 Edelbrock Corp

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:

[email protected].

•

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 dyno-

matched 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
3.

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.

(c) Install the three cam gear capscrews; lightly tighten.

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.