Engine Accessory Hardware

Engine accessory hardware fastens the parts mounted on the outside of the engine and gearbox: ignition coils, distributors, mechanical fuel pumps, superchargers, valve covers and transmission cases. ARP bolt and stud kits replace the factory hardware on these parts, and universal stainless accessory studs are listed alongside.

Accessory joints are rarely highly loaded, but they live with constant vibration. Their usual failure is self-loosening: each time the joint slips sideways under vibration, the fastener turns back a little. Enough clamp load stops the slip, and matched fasteners tightened to one figure make that clamp load consistent across the joint.

Studs help in two ways. They locate a heavy part, such as a supercharger or a bracket, while it is lowered into place, and they spare aluminium threads from repeated removal. A common rule of thumb is that a steel fastener in aluminium needs thread engagement of about twice its diameter.

The titles describe each kit:

• Engine and gearbox kits: coil and coil-bracket bolts, distributor studs, fuel pump bolts, valve cover bolts, case bolts and studs, and transmission mount studs.
• Universal studs: stainless accessory studs in packs of 8, such as M8 x 1.25 in 51 mm or 57 mm lengths, and M10 x 1.25 at 48 mm.
• Supercharger studs: aluminium blower stud kits, such as 7/16 x 2.500 in or 7/16 x 2.880 in, including a break-away version.
• Finish and head: black oxide or stainless steel, with 12-point or hex heads in socket sizes such as 3/8 in, 1/2 in, 8 mm and 12 mm.
• Other items: plate retaining clips in 1/4-28 and 10-32, a drive flange kit, an M12 x 1.50 wheel stud kit and coil pack covers.

Tighten to the figure for the part being clamped, not to what a strong fastener could take. A thin bracket or an aluminium thread can give way long before the fastener does. Fit studs finger-tight, using a hex key where they have a socket in the end. Use thread-locking compound where the original assembly called for it, and the specified lubricant elsewhere.

On a gearbox case, tighten the bolts gradually in a cross pattern so the halves pull together evenly. After fitting, make sure no wiring, hose or cable is trapped, and re-check the fasteners after the first run.