Reinforced head gasket Mazda 1.6 B6ZE B64F B6MC B6MU 8AN1 B6T

The Mazda engines covered

The B6ZE, B64F, B6MC, B6MU, 8AN1 and B6T are 1.6 litre four-cylinder petrol engines. They power the Mazda MX-5 (NA and NB) and 323 (BF and BG), the Australian Ford Capri and Laser, the Mercury Capri and the Haima Premacy listed in the compatibility table below.

The original gaskets carry part numbers B660-10-271 ; B660-10-271A ; B660-10-271B ; B660-10-271C ; B660-10-271D ; B6F4-10-271A ; B6F4-10-271B. Mazda publishes neither their bore, nor their thickness, nor their construction. Each engine takes one cylinder head gasket, sized for the standard combustion pressure; when that pressure climbs, the clamping force eases, the head lifts slightly and coolant seeps into a cylinder.

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. So also check the head bolts of your Mazda before reassembly.

This page brings together the part numbers of two competition manufacturers, Athena and Cometic, in two constructions: the stainless-ring O-Ring, with part number 330145R in 1.40 mm, and the multi-layer steel MLS, with 18 C4122 part numbers from 0.69 to 3.56 mm. All the gaskets have an 80 mm bore 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. On this page, compare only gaskets with an 80 mm 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. Do this on the head and on the block of your Mazda, whichever B6 engine it has.

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. Here, it is part number 330145R, in an 80 mm bore and 1.40 mm thick.

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. Here, these are the C4122 part numbers, in an 80 mm bore.

Choosing bore and thickness

Gasket bore. The Athena O-Ring (330145R) and the Cometic MLS (C4122) each come in 80 mm.

Thickness. No thickness is published for the original gaskets B660-10-271 ; B660-10-271A ; B660-10-271B ; B660-10-271C ; B660-10-271D ; B6F4-10-271A ; B6F4-10-271B. 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. On these four-cylinder engines, take that measurement at each of the four pistons.

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. Its part number 330145R appears on this page, in an 80 mm bore.
	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. For these engines, it offers a series of part numbers here in an 80 mm bore.

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 80 mm bore of these gaskets 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: B660-10-271 ; B660-10-271A ; B660-10-271B ; B660-10-271C ; B660-10-271D ; B6F4-10-271A ; B6F4-10-271B.

Important: the part numbers on this page suit only the B6ZE, B64F, B6MC, B6MU, 8AN1 and B6T engines: check your Mazda'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. For the Mazda B6 engines on this page, it is the answer as soon as the original output is exceeded.

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. On the Mazda B6 engines on this page, from the B6ZE to the B6T, it is the first point to watch.