Standards
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Main Cap Bolts
Main cap bolts (and the closely related main studs) clamp the main bearing caps to the engine block and support the crankshaft against the firing-stroke loads that beat down on the main bearings every revolution. They are widely upgraded in boosted, high-RPM, and stroker builds because OE main bolts are sized for OE peak cylinder pressure and OE redline; once boost climbs or stroke lengthens, OE main bolts can lose preload, walk the cap, and spin a main bearing. The 12-point head is the standard drive geometry on main cap bolts because the main-saddle pocket is shallow, the windage tray and oil-pickup clearances are tight, and the twelve splines allow the high applied torque needed for repeatable preload in that limited socket-clearance window.
TorqBolt manufactures main cap bolts and main studs in Custom 465 (260 ksi corrosion-resistant), AISI 8740 chromoly heat-treated (220 ksi), AISI 4340, MP35N (sour-service or marine), L19 race-grade alloy steel and 17-4 PH H1025 to AS9100D Rev D and ISO 9001:2015 quality systems. Each bolt or stud carries the struck tB manufacturer ligature plus the alloy grade marking, and every lot ships with a mill test report (MTC 3.1 standard, MTC 3.2 critical with hardness, tensile, magnetic-particle and shot-peen-after-thread-roll process inspection records).
Materials
Alloy choice is set by the spec, the service temperature, the corrosion environment, and the strength target. TorqBolt routinely produces main cap bolts in A286 (UNS S66286), Inconel 718, Ti-6Al-4V (Grade 5), MP35N (UNS R30035), Custom 465 stainless, AISI 8740 chromoly heat-treated, AISI 4340, 17-4 PH H1025 condition, H-11 tool steel, and L19 race-grade alloy steel.
Main bearing cap clamp loads
Main cap bolts retain the bearing cap that holds the crank in the block. The cap clamp determines the radial stiffness of the main bearing and thus the rotating-assembly precision under load. Race builds often replace the standard 4-bolt-per-cap arrangement with a 4+2 cross-bolted configuration that adds two side bolts to lock the cap against block movement. Cross-bolt 12-point flange bolts in 12-point flange-head form work well for the side-bolt application. Standard main caps use 12-point head bolts or 12-point studs.
Request a Quote
RFQ to info@torqbolt.com, call +91-22-66157017, or WhatsApp +91-22-66157017. Mill test report (MTC 3.1 standard, 3.2 critical-service) ships with every lot.
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