RCM over-sized head stud kits provide maximum head gasket sealing by resisting head lift under extreme cylinder pressures. RCM's unique 14/12mm head stud option uses a 14 x 2.00mm thread on the block side and a 12 x 1.25mm thread on the head side thus allowing these studs to be used with no or minimal modification to the head castings or gaskets (only the block side requires modification). Manufactured from aircraft grade S99 high-tensile steel with precision rolled threads.
Each kit includes 12 head studs, 12 nuts, and assembly lube. The flanged nuts do not require washers for proper installation.
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What is the advantage of head studs over head bolts? A properly installed head stud will provide more accurate and consistent clamping force which will improve head gasket reliability. A head bolt will twist as it is being torqued meaning that only a portion of the torque loading will be in the vertical direction.
What is the S99 alloy used for these head studs? S99 is a British specification for aircraft/aerospace nickel-chromium-molybdenum steel. It can be heat treated to wide range of tensile strengths. There is no direct US equivalent alloy. The specification used by RCM has a minimum tensile strength of 237,000psi putting it somewhere between ARP2000 and ARP L19 in terms of tensile strength.
When should I use this head stud? Our general recommendation would be ARP2000 11mm up to 450bhp, ARP CA625+ up to 600bhp, RCM 14/12mm up to 650bhp, and 14mm for anything beyond that.
When other considerations do I need to take into account when selecting head studs? The higher the torque level applied to the head studs the more the block will distort due to forces exerted on the material around the bolt holes. This distortion in the cylinders (and to a lesser degree in the main bearing line bore) should ideally be corrected by torque plate honing (and line bored if the main bearing bores are signficantly out of round). Anything more substantial than an ARP 11mm head stud will need the cylinders bored & honed oversized for best results.
