Flywheel / Pressure Plate Bolts

Flywheel bolts clamp the flywheel or flexplate to the crankshaft flange, and pressure plate bolts clamp the clutch cover to the flywheel. All of the engine’s torque passes through the flywheel joint, and a share of it through the clutch cover. ARP kits for both are listed here by engine, together with bellhousing bolt and stud kits.

The torque is not meant to pass through the flywheel bolts in shear. It passes by friction between the flywheel and the crank flange, and that friction comes from the bolts’ clamp load. If the clamp load falls short, the flywheel can creep on the flange; the faces fret, the bolts start to take shear and bending, and fatigue can follow.

Hard launches, heavy flywheels and high-clamp clutches all add to the load on this joint. Many factory flywheel bolts are stretch bolts designed for a single use, so they should not be refitted.

Check these points against your parts:

• Thread and length: threads such as M10 x 1.00, M12 x 1.25, 7/16-20 or 1/2-20. Many kits also give the under-head length (UHL), such as 0.700, 0.875 or 1.000 in.
• Flywheel thickness: an aftermarket flywheel may be thicker or thinner at the bolt circle than the original. A bolt that is too long can bottom out, while one that is too short leaves too little thread in the crank.
• Flywheel or flexplate: separate kits cover manual flywheels, automatic flexplates, flexplates used with an adapter plate, and pressure plates.
• Head and drive: hex or 12-point, with some 12 mm tri-square and internal drives where the design calls for them.
• Material: mostly 8740 chrome moly, with L19 listed too. Bellhousing bolts come in polished stainless steel as well.
• Bellhousing studs: such as 1/2 in bellhousing-to-transmission studs, which help guide the gearbox into place.

Clean the crank threads and flange of old thread-locking compound and oil. Where a bolt hole breaks through into the crankcase, seal the threads so that oil cannot weep onto the clutch. Follow the kit’s instructions on lubricant or thread-locking compound, as either changes the torque needed.

Lock the flywheel with a holding tool, then tighten its bolts in a star pattern and in stages. Centre the clutch plate with an alignment tool, and tighten the pressure plate bolts evenly in a cross pattern so the cover is not distorted. Do not use an impact wrench on either joint.