Reinforced cylinder head gasket MG TC, TD and TF XPAG XPEG

The MG engines covered

The Morris XPAG engine of 1,250 cc and the XPEG engine of 1,500 cc power the MG TC, TD and TF, detailed below.

The original gaskets carry the part numbers AAA5841 for the XPAG (MG TD up to engine 22734, oval water passage) and AEF140 for the XPEG (MG TF 1500). The manufacturer publishes neither their bore, nor their thickness, nor their construction. Sized for the original combustion pressure, they are no longer enough once it rises: the clamping load fades, the head lifts slightly and coolant reaches a cylinder.

Reinforced cylinder head gaskets

Sealing also depends on the bolts or studs that clamp the head to the block, not only on the gasket. Pure 99.9% copper does not fear corrosion, crushes without cracking and carries heat away well, even at high temperature.

This page presents the three part numbers from the American maker Cometic, a specialist in racing gaskets, in a single construction: copper. Two bores are offered, 68 mm for the XPAG and 74 mm for the XPEG; the thickness is 0.69 mm or 1.09 mm. The gasket is cut with valve pockets and is sold individually.

Technical specifications

A gasket's volume is the void it leaves above each cylinder: it swells the combustion chamber and lowers the compression ratio. Two gaskets can only be compared at the same bore.

Preparation and fitting

Before fitting, run a straightedge over the head and the block to check their flatness, and have whatever needs it resurfaced. Cometic checks the flatness of each copper gasket before it ships.

Technical guide

The construction offered

Choosing bore and thickness

Gasket bore. The Cometic copper gaskets exist in 68 mm (C4309-027 and C4309-043) and in 74 mm (C4310-043).

Thickness. No thickness is stated by the manufacturer for the original gasket. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

With no published original thickness, use a dial gauge to read how far the pistons protrude above the block face, above all to aim for 0.69 mm: that figure gives the clearance left between piston and head.

The brand

Cometic Gasket, Inc. is an American company, founded in 1989 in Concord, Ohio, that designs gaskets and sealing solutions for engines. It is known for the made-to-measure gasket, cut to the bore and thickness wanted, and everything is made 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 74 mm bore, the largest 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: AAA5841 (XPAG) and AEF140 (XPEG).

Important: the part numbers on this page suit the XPAG (68 mm) and XPEG (74 mm) engines: check your engine code and the bore of your head before ordering.

Why switch to a reinforced gasket?

When the original gasket is spent, this copper gasket replaces it: pure copper stays ductile when hot without turning brittle, which preserves the seal between head and block.

On an engine pushed close to its limits, the head gasket is frequently the first part to give way. The reinforced gasket prevents the leak and costs far less than the head removal it would entail, without keeping the car off the road for long.