Reinforced cylinder head gasket BMW M88B35 S38B35 S38B36 S38B38

The BMW engines covered

The BMW M88B35, S38B35, S38B36 and S38B38 are inline six-cylinder petrol engines with twenty-four valves. They power the M1 (E26), the M635CSi (E24) and the M5 (E28 and E34) listed below. The first three take the same original cylinder head gasket, while the S38B38 takes its own.

This original gasket carries the part number 11 12 1 316 705. BMW does not state its construction, only that it is asbestos-free; its bore is 94.5 mm and its thickness 1.74 mm. It is sized for standard combustion pressure and settles as soon as that pressure rises: the clamping load relaxes, the cylinder head lifts and coolant finds its way into a cylinder. The S38B38 takes the 11 12 1 401 351, with a 95.5 mm bore and a thickness of 1.82 mm.

Reinforced cylinder head gaskets

The seal does not come from the gasket alone: it depends on the fasteners, which clamp the cylinder head onto the block. A composite gasket is crushed for good above 100 N/mm² of allowable stress, whereas the 301 stainless steel of the MLS withstands 517 N/mm², 5 times more, and springs back at every combustion. The O-Ring works differently: its single stainless ring seals the chamber, while the gasket body handles water and oil, with no machining of the block.

This page gathers the part numbers of two racing manufacturers, Athena and Cometic, in two constructions: the O-Ring with a stainless ring and the multi-layer steel MLS. Gasket bores are 95 mm, except the 330017R at 95.6 mm, and the thicknesses run from 0.69 to 3.56 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

The gasket volume is the space it leaves above each cylinder. It adds to the combustion chamber: the larger it is, the lower the compression ratio. Compare these values only between gaskets of the same bore.

Preparation and fitting

Before fitting, check the flatness of the cylinder head and block faces with a straightedge, and have them resurfaced if needed. No gasket sealant is required: Athena and Cometic supply these 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 compression ring around each cylinder. The ring concentrates the clamping force on a small diameter, exactly where the sealing happens, and a silicone bead protects the water and oil passages. It is the construction that withstands the highest pressures, and the only one suited to a cylinder head already prepared with a compression wire.

Cometic MLS An assembly of stamped, riveted stainless steel sheets. The outer sheets show active beads around each cylinder and each fluid passage. A moderate clamping load is enough to seal and the bore distorts little: it is the all-round answer, from the tuned naturally aspirated engine to moderate boost.

Choosing bore and thickness

Gasket bore. The Athena O-Ring comes in 95 mm (330061R) and 95.6 mm (330017R), the Cometic MLS in 95 mm (C4478).

Thickness. The original gasket has a thickness of 1.74 mm (1.82 mm for the S38B38). 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 the original, measure with a dial gauge how far the pistons stand proud of the block face: it sets the clearance left between piston and cylinder head.

The two brands

	Athena S.p.A. is an Italian maker of gaskets and engine parts, based in Alonte, in the Veneto, home to its main factory. It also has sites in Spain, the United States, Brazil and India. Several car makers fit its multi-layer gaskets as original equipment, and its entire competition range is designed and made in Italy.
	Cometic Gasket, Inc. is an American company, founded in 1989 in Concord, Ohio, that specialises in engine gaskets and sealing. Its reputation rests on the made-to-order gasket, supplied in the bore and thickness requested, and all 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 94.5 mm 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 1 316 705 (M88B35, S38B35 and S38B36) and 11 12 1 401 351 (S38B38), asbestos-free.

Important: the Cometic C4478 and the Athena 330061R suit the M88B35, S38B35 and S38B36. The S38B38 takes a different original cylinder head gasket (part number 11 12 1 401 351, 95.5 mm bore, 1.82 mm thickness), for which the Athena 330017R is intended: check your vehicle's engine code before ordering.

Why switch to a reinforced gasket?

Once the original gasket is no longer enough, the reinforced version stays in control: under higher combustion pressure it keeps its shape instead of flattening.

As soon as power goes up, through a supercharger, a turbo or a raised compression ratio, the head gasket is the first part of the top end to give way. Choosing a reinforced gasket means choosing reliability: you spare yourself the failure and the cylinder head removal that follows.