Reinforced cylinder head gasket BMW S63B44 N63B44

The BMW engines covered

The BMW S63B44 and N63B44 are 4.4 litre, 32-valve twin-turbo petrol V8 engines. They power the 5 Series (F10, F11 and F07), 6 Series (F06, F12 and F13), 7 Series (F01 to F04), X5 (E70, F15 and F85) and X6 (E71, E72, F16 and F86) models in the table below. The gasket is sold individually: a V8 needs two, one per cylinder head.

The original gasket carries part number 11 12 8 008 122, which replaces the 11 12 7 567 765 fitted before October 2015. It is 0.75 mm thick; the repair size, 11 12 8 008 118, measures 1.05 mm, which is 0.30 mm more. BMW publishes neither its bore nor its construction. It is sized for standard combustion pressure: when that rises, the clamping load drops, the head lifts and coolant reaches a cylinder.

Reinforced cylinder head gaskets

The head gasket does not make the seal alone: it holds because the fasteners clamp the head down onto the block. Beyond 100 N/mm² of admissible stress a composite gasket is crushed for good, whereas the 301 stainless steel of the MLX withstands 517 N/mm², 5 times more, and recovers its shape at each combustion. The O-Ring shares out the roles differently: the stainless ring alone isolates the combustion chamber, the gasket body closes the water and oil circuits, and the block needs no machining.

This page brings together the part numbers of two racing manufacturers, Athena and Cometic, in two constructions: O-Ring with a stainless ring and MLX with a combustion stopper. The gasket bores run from 90 to 90.5 mm and the thicknesses from 0.81 to 1.10 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 and for one cylinder bank only: one is needed on the right and one on the left.

Technical specifications

Gasket volume: the room the gasket leaves free above each cylinder. It adds to the combustion chamber, so the larger it is, the lower the compression ratio. These values can only be compared between gaskets of the same bore.

Preparation and fitting

Before fitting, check with a straight edge that the head and the block are flat, and have them resurfaced if needed. No sealant is needed: Athena and Cometic supply their gaskets already coated.

Technical guide

The two constructions offered

	Athena O-Ring / Cut Ring A steel sheet coated with asbestos-free aramid fibre, with a stainless steel compression ring crimped around each cylinder. The ring concentrates the clamping load on a narrow band, exactly where the seal is made, while a silicone bead protects the water and oil passages. This construction withstands the highest pressures and suits a head prepared with a compression wire.
	Cometic MLX A stack of stamped, riveted stainless steel sheets, with a folded centre sheet forming a stopper around the combustion chamber, and a high-temperature coating. The clamping load rises locally without increasing bore distortion. It is the strongest of the all-steel gaskets, to choose for high boost, in 90 mm only.

Choosing bore and thickness

Gasket bore. The Athena O-Ring comes in 90.5 mm, the Cometic MLX in 90 mm.

Thickness. The original gasket is 0.75 mm thick. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

As every thickness offered exceeds the original by at least 0.06 mm, the compression ratio drops slightly. Still measure with a dial gauge how far the pistons stand proud of the block: it gives the clearance left between piston and head.

The two brands

	Based in Alonte, in the Veneto, where its head office and main plant are located, Athena S.p.A. designs gaskets and engine parts. It also has sites in Spain, the United States, Brazil and India. Car makers fit its multi-layer gaskets as original equipment, and its competition range is entirely drawn and built in Italy.
	Founded in 1989 and based in Concord, Ohio, Cometic Gasket, Inc. is an American company that designs gaskets and sealing solutions for engines. It has specialised in made-to-order gaskets, with the bore and thickness you want, and makes everything in the United States, from 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 gaskets offered (90 to 90.5 mm) 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 8 008 122 (11 12 7 567 765 before October 2015) in standard size, 11 12 8 008 118 (11 12 7 567 764 before October 2015) in repair size.

Important: the S63B44 of the M5 F90, the M8, the X5 M F95 and the X6 M F96 take a different original head gasket, part numbers 11 12 7 853 634 and 11 12 7 853 635. These vehicles are not covered by the part numbers on this page.

Why switch to a reinforced gasket?

Where the original gasket reaches its limit, the reinforced one keeps holding: under higher combustion pressure it keeps its shape instead of being crushed.

With a bigger turbo, a higher boost pressure or a changed compression ratio, power climbs and the head gasket becomes the weak link of the top end. A reinforced gasket is then no luxury: it prevents the leak and the head removal that follows.