Reinforced cylinder head gasket BMW and Toyota B58B30

The BMW and Toyota engines covered

The BMW B58 is the 3.0-litre turbocharged inline six-cylinder petrol engine, with an 82 mm bore and a 94.6 mm stroke, built since 2015. It powers most BMW ranges, from the 1 Series to the 8 Series by way of the X3 to X7 and the Z4, as well as the Toyota GR Supra. Four engine codes are covered: the B58B30A, first generation, then the B58B30B, B58B30C and B58B30O1, second generation.

The original gaskets carry two part numbers depending on the engine code. The 11 12 8 654 268 is fitted to the B58B30A: BMW gives it a thickness of 0.70 mm and lists a repair size, the 11 12 8 654 269, at 1.00 mm. The 11 12 7 934 583 is fitted to the B58B30B, B58B30C and B58B30O1: BMW publishes neither its construction, nor its bore, nor its thickness. Each engine receives only one. It is calibrated for the original combustion pressure: when that rises, the clamp load relaxes, the head lifts and coolant gets into a cylinder.

Reinforced cylinder head gaskets

A cylinder head gasket does not seal on its own: the seal depends on the fasteners, which clamp the head against the block. A composite gasket is crushed for good beyond 100 N/mm² of allowable stress; the 301 stainless steel of the MLX withstands 517 N/mm², 5 times more, and regains its shape at every combustion. The O-Ring shares the roles differently: its stainless ring alone seals the combustion, the body handles the water and oil passages, and nothing needs machining in the block.

This page brings together the part numbers of two racing manufacturers, Athena and Cometic, in three constructions: O-Ring with a stainless steel ring, MLX with a combustion chamber stopper and DST with a double stopper. The gasket bores are 83, 84 and 84.5 mm, all larger than the engine's 82 mm bore, and the thicknesses run from 0.91 to 1.80 mm, enough to adjust the compression ratio without touching the pistons or the cylinder head. As a rule, the gasket bore chosen is at least 0.5 mm larger than the actual cylinder bore. Each part number is sold individually, one gasket per engine.

Technical specifications

Gasket volume: the space the gasket provides above each cylinder. It adds to the combustion chamber, so the larger it is, the lower the compression ratio. Only compare values between gaskets of the same bore.

Preparation and fitting

Before assembly, check the flatness of the cylinder head and of the block with a straightedge, and have them machined if needed. None of these gaskets needs sealing compound: Athena and Cometic supply them already coated.

Technical guide

The three constructions offered

	Cometic DST Seven stainless steel sheets stacked together: two full-surface sheets, carefully folded to act as stoppers, are paired with embossed sealing sheets that carry Cometic's own coating. The clamp load spreads evenly between the head and the block, which cuts bore distortion noticeably and makes the seal more dependable. The DST goes on as supplied: no further machining of the head, no groove and no o-ring, which are normally demanded under extreme boost. It builds on Cometic's MLX stopper design.
	Cometic MLX Stacked stainless steel sheets whose folded centre sheet forms a stopper around the combustion chamber, together with a high temperature coating. Local clamping rises without increasing bore distortion. To be chosen when boost calls for a sturdy all-steel gasket, in 83 mm only.
	Athena O-Ring / Cut Ring A steel sheet faced with asbestos-free aramid fibre, ringed at each cylinder by a stainless steel compression ring. The ring carries the clamp load onto a small diameter, where the seal is made, while a bead of silicone protects the water and oil passages. It is the construction that withstands the highest pressures, and the only one compatible with a head already prepared with a compression wire.

Choosing bore and thickness

Gasket bore. The Athena O-Ring comes in 83, 84 and 84.5 mm; the Cometic MLX and the Cometic DST come in 83 mm only.

Thickness. The original gasket of the B58B30A is 0.70 mm thick; BMW does not publish the thickness of the one fitted to the B58B30B, B58B30C and B58B30O1. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

If you choose a thickness below that of the original gasket, use a dial gauge to measure how far your pistons stand proud of the block: it decides the clearance left between the piston and the head.

The two brands

	Athena S.p.A., an Italian maker of gaskets and engine components, has its head office and main plant in Alonte, in the Veneto. Other production sites are in Spain, the United States, Brazil and India. Car manufacturers fit its multilayer gaskets as original equipment, and the competition range is designed and made entirely in Italy.
	Cometic Gasket, Inc. is an American maker of engine gaskets and sealing solutions, set up in 1989 and based in Concord, Ohio. It specialises in made-to-order gaskets, in the bore and thickness required. All of its production stays in the United States, using American materials.

Advantages over the original gasket

When a reinforced gasket becomes necessary

• Adding forced induction, or raising boost on an already turbocharged engine
• Cylinder rebored beyond what the bore of the original gasket covers
• Looking for a compression ratio different from standard, higher or lower
• Engine that has already lost its gasket, or is consuming coolant
• Competition use, where the gasket goes through repeated temperature rises

Vehicle compatibility

OEM part number: 11 12 8 654 268 for the B58B30A (repair size 11 12 8 654 269), 11 12 7 934 583 for the B58B30B, B58B30C and B58B30O1.

Important: the part numbers on this page do not all fit every engine code. The B58B30A takes the 330212R O-Ring and the C14121 MLX; the B58B30B takes the 330155R and 330190R O-Rings and the C14144 MLX; the B58B30C and B58B30O1 take the C14144 MLX and the C14208 DST. Check your vehicle's engine code before ordering.

Why switch to a reinforced gasket?

The reinforced gasket keeps its shape instead of being crushed when combustion pressure goes beyond the limit of the original gasket.

As soon as power increases, with a turbo, a supercharger or a raised compression ratio, the head gasket becomes the weak point of the top end. Choosing a reinforced one is then a matter of safety rather than comfort: it avoids the failure and the cylinder head removal that follows.