Reinforced cylinder head gasket BMW S63B44T4

The BMW engines covered

The S63B44T4 is the 4.4 litre, 32-valve twin-turbo petrol V8 of the latest generation of BMW M cars. It powers the M5 (F90), M8 (F91, F92 and F93), X5 M (F95) and X6 M (F96) listed in the table below. The gasket is sold individually and the engine needs two, one per cylinder head.

BMW lists this original gasket under part number 11 12 7 853 634, at 0.80 mm; the repair size, 11 12 7 853 635, is 0.30 mm thicker and measures 1.10 mm. The manufacturer does not publish its bore or its construction. Sized for standard combustion pressure, it gives up once that pressure is exceeded: the head lifts slightly, clamping load drops and coolant reaches the cylinder.

Reinforced cylinder head gaskets

The seal does not depend on the gasket alone: the fasteners that clamp the head onto the block provide the other half. A composite gasket is permanently crushed beyond 100 N/mm² of stress, whereas the 301 stainless steel of the MLX withstands 517 N/mm², five times more, and springs back on every combustion cycle.

This page covers one part number from Cometic, the American maker of competition gaskets, in a single construction: MLX. Its bore is 92 mm and its thickness 0.81 mm, barely more than the original, so the compression ratio stays practically unchanged. It is sold individually: plan on two gaskets for the V8.

Technical specifications

Gasket volume is the space the gasket leaves free above each cylinder. It adds to the combustion chamber, so the larger it is, the lower the compression ratio. This value only means something when comparing gaskets of the same bore.

Preparation and fitting

Before fitting, check head and block for flatness with a straight edge, and have the faces resurfaced if needed. The Cometic gasket arrives pre-coated: do not add any sealant.

Technical guide

The construction offered

Cometic MLX A stack of stamped, riveted stainless steel sheets whose centre sheet is folded to form a stopper around the combustion chamber, with a high-temperature coating. Clamping force rises at that point without any extra bore distortion. It is the strongest all-steel construction, recommended for heavy boost, here in 92 mm.

Choosing bore and thickness

Gasket bore. The Cometic MLX comes in 92 mm (C14206-032), with no other bore.

Thickness. The original gasket is 0.80 mm thick. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

The thickness offered, 0.81 mm, differs from the original by only 0.01 mm, so the compression ratio stays practically unchanged. Still measure with a dial gauge how far the pistons stand proud of the block deck, then work out the clearance left between piston and head.

The brand

Cometic Gasket, Inc. is an American company founded in 1989 and based in Concord, Ohio, which designs gaskets and sealing solutions for engines. Its strength is the made-to-order gasket, cut to the bore and thickness required, manufactured entirely in the United States from American raw 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 92 mm bore of the gasket offered 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 7 853 634 in standard size, 11 12 7 853 635 in repair size.

Important: the S63B44 of the M5 F10 and the M6 F06, F12 and F13 take a different original head gasket, part numbers 11 12 8 008 122 and 11 12 8 008 118. These vehicles are not covered by the part number on this page.

Why switch to a reinforced gasket?

When the original gasket reaches its limit, the reinforced one takes over: under high combustion pressure it keeps its shape and does not collapse.

With a bigger turbo, more boost or a raised compression ratio, the head gasket is the first part of the top end to give way. A reinforced gasket prevents the leak and the head removal that follows, a job far more expensive than the part itself.