Reinforced head gasket Austin Mini Allegro Maestro Metro 12H 9FE

The Austin engines covered

The 12H and 9FE are 1.3-litre four-cylinder petrol engines. They power the Austin Mini, Allegro, Maestro, Metro, America and 1000 models listed in the compatibility table below.

The original gasket carries part number AEG226. Austin publishes neither its bore, nor its thickness, nor its construction. An engine takes a single 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

Sealing does not rest on the gasket alone: it also depends on the fasteners that clamp the head against the block. Beyond 100 N/mm², a composite gasket settles for good; the 301 stainless steel of MLS gaskets withstands 517 N/mm², 5 times more, and springs back at every combustion. Also inspect the head bolts or studs of your Austin and replace any that are stretched or damaged.

This page groups 19 part numbers from Cometic, the American maker of competition gaskets, in two constructions: MLS, multi-layer steel (15 part numbers), and copper (4 part numbers). The bores run from 71 to 73.5 mm and the thicknesses from 0.69 to 3.56 mm. An engine takes only one gasket: order a single part number. Choosing the thickness lets you tune the compression ratio without working on 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

A gasket's volume is the free space it leaves above each cylinder: it is added to the combustion chamber and lowers the compression ratio. Comparison only makes sense between gaskets of the same bore, and this page offers five, from 71 to 73.5 mm.

Preparation and fitting

Before fitting, check with a straightedge that the joint faces of the head and the block are flat, and have them resurfaced if necessary. Cometic gaskets arrive ready to fit: apply no sealing paste. Clean both faces thoroughly before laying the gasket. This applies to the head and to the block of your Austin alike.

Technical guide

The two constructions offered

	Cometic copper A sheet of pure oxygen-free copper, grade C110, at 99.9% copper. The metal resists corrosion, compresses without cracking, carries heat away well and stays supple at high temperature. Cometic checks the flatness of every gasket and advises fitting it with a crimped sealing ring. 4 part numbers on this page are copper.
	Cometic MLS Stainless steel plates, stamped, stacked and joined by rivets. The outer plates carry active beads that follow the outline of each cylinder and each fluid channel. A moderate clamping load is enough to seal and the bore distorts little: a versatile construction, from the tuned naturally aspirated engine to light forced induction. 15 of the 19 part numbers on this page are MLS.

Choosing bore and thickness

Gasket bore. Cometic part numbers come in five bores: 71 mm (H0525SPB040S), 72 mm (C14046, H0525SPU030S and H0525SPM030S), 72.5 mm (C14073 and C14050), 73 mm (C4146) and 73.5 mm (C14038, H0525SPD030S and H0525SPC030S).

Thickness. Austin publishes no thickness for the original gasket AEG226. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

If you are aiming for a thickness below that of the gasket removed, use a dial gauge to measure how far each piston protrudes above the block's joint face: it determines the clearance left between piston and head. Take this reading at every cylinder.

The brand

Cometic Gasket, Inc., created in 1989 and based in Concord, Ohio, is an American company specialising in gaskets and sealing parts for engines. It owes its reputation to made-to-measure gaskets, cut to the bore and thickness required and manufactured in the United States from American materials. For these Austin engines, its part numbers are offered here in five bores, from 71 to 73.5 mm.

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 71, 72, 72.5, 73 and 73.5 mm bores of the gaskets 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: AEG226.

Important: the part numbers on this page suit only the 12H and 9FE engines: check your Austin's engine code before ordering.

Why switch to a reinforced gasket?

When the original gasket has nothing left to give, the reinforced gasket steps in: under higher combustion pressure the steel MLS keeps its shape instead of crushing, and the copper, supple when hot, maintains the seal. On the Austin engines on this page, it becomes useful as soon as the engine exceeds its original output.

Forced induction added, compression ratio raised or revs pushed up by livelier camshafts: each time, the cylinder head gasket becomes the weak point of the tuned engine. A reinforced gasket prevents the leak, and the head removal it would bring costs far more than the part. On these 1.3-litre engines, it is the first point to deal with as soon as you go beyond the original output.