COMP Cams 4120 Gear Drive System - Manual

COMP Cams®
3406 Democrat Rd.
Memphis, TN 38118
Phone: (901) 795-2400 Fax: (901) 366-1807
www.compcams.com
Part #118
Revised 5/31/13
COMP Cams
®
Gear Drive System
#4120 Ford Small Block
Thank you for choosing COMP Cams
®
products; we are proud to be your manufacturer of choice.
Please read this instruction sheet carefully before beginning installation, and also take a moment to
review the included limited warranty information.
Notes :
1. The installation procedures which follow assume that the engine has been disassembled and
cleaned as it would be for a normal timing set change.
2. The reverse idler gear should have between .005" and .070" in vertical travel when the set is
installed on the engine with the power idler in hard mesh between the crank and cam gears. If
this is not the case excessive, heat can be generated causing damage to the gear set.
3. The purpose of the reverse idler gear is to prevent the power idler from disengaging when the
crankshaft rotates backwards as happens in shutting off the engine.
4. The engine is timed with the timing marks facing one another just as you would with a chain
and sprocket drive.
5. Idler pins will always be in contact with the timing cover during use. Back of idler pins must
have a minimum of .015" clearance to block.
6. On small block engines the rib on the inside of the timing cover must be removed.
7. The Dual Idler Gear Drive is intended for use with a harmonic balancer. It is not for use with
an aluminum hub.
Installation Instructions:
1.
With a dab of grease install bronze wear ring, included in kit on the back of cam gear.
2. Install cam gear on engine and install fuel pump eccentric and bolt. We recommend a one
piece eccentric but a two piece eccentric if a spacer is placed behind the eccentric so that the
outer ring can spin freely. Torque camshaft bolt to factory spec. Late model small blocks use
a .251” thrust plate. Early models use a .217" thrust plate. 351C engines use a .156" thrust
plate.
INSTRUCTIONS