Reinforced head gasket MG MGA Magnette 15GB 16GA 16GB 16GC

The MG engines covered

The 15GB, 16GA, 16GB and 16GC are BMC B-Series petrol engines. They power the MG Magnette and MGA models listed in the compatibility table below.

MG publishes no data on the original gasket: no part number, no bore, no thickness and no construction. It is sized for the standard combustion pressure; as soon as that pressure rises, the clamping load relaxes, the head lifts slightly and coolant seeps into a cylinder.

Reinforced cylinder head gaskets

Sealing does not rely on the gasket alone: it also depends on the fasteners that press the head onto the block. Beyond 100 N/mm², a composite gasket settles with no recovery; the 301 stainless steel of MLS gaskets withstands 517 N/mm², 5 times more, and returns to shape at every combustion. Also examine the head fasteners of your MG and replace any that are stretched or damaged.

This page groups 4 part numbers from Cometic, the American maker of competition gaskets, in a single construction: MLS, multi-layer steel. The bore is unique, 74 mm, and the 4 thicknesses run from 0.76 to 1.30 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, here 74 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 MG alike.

Technical guide

The construction offered

Cometic MLS Stainless steel sheets, stamped and joined by rivets. The outer sheets carry active beads that follow the outline of the cylinders and of the fluid passages. A moderate clamping load is enough to seal, and the bore distorts little. This versatile gasket suits everything from the tuned naturally aspirated engine to light forced induction. All 4 part numbers on this page are offered in this construction, for the MG engines 15GB, 16GA, 16GB and 16GC.

Choosing bore and thickness

Gasket bore. The Cometic MLS is offered in a single bore, 74 mm (C4359).

Thickness. The manufacturer publishes no thickness for the original gasket: the thickness of the gasket you removed serves as the reference. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

To settle on a thickness below that of the removed gasket, use a dial gauge to read how far each piston stands proud of the block's joint face: that height sets the clearance left between piston and head. Take the measurement 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 MG engines, its part numbers are offered here in a single 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 74 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: not published by the manufacturer.

Important: the part numbers on this page suit only the 15GB, 16GA, 16GB and 16GC engines: check your MG's engine code before ordering.

Why switch to a reinforced gasket?

When the original gasket is spent, the reinforced gasket takes over: under higher combustion pressure it keeps its shape instead of collapsing. On the MG engines on this page, it becomes necessary 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 MG B-Series engines, it is the first point to deal with as soon as you go beyond the original output.