Reinforced cylinder head gasket Peugeot 309 405 Citroën BX 1.9 XU9J4 XU9J4Z 159K

The Peugeot and Citroën engines covered

The petrol engines XU9J4, XU9J4Z and 159K, PSA 1.9-litre four-cylinders rated 145 to 160 hp, are the engines covered by this page. They power the Peugeot 309 GTI 16V and 405 (Mi16, 4x4, Break) and the Citroën BX 19 GTi models listed in the compatibility table below.

The original gasket fitted to these engines carries part number 0209.L3. Peugeot and Citroën publish neither its bore, nor its thickness, nor its construction. It is sized for standard combustion pressure: as soon as it rises, the clamping load drops, the head lifts and coolant passes into a cylinder.

Reinforced cylinder head gaskets

The head studs or bolts alone provide half of the sealing: the gasket never works alone. A composite gasket is crushed permanently from 100 N/mm², whereas the 301 stainless steel of an MLS gasket withstands 517 N/mm², five times more, and recovers its shape with every combustion.

This page groups two part numbers from Athena, an Italian maker of racing gaskets, for a single construction: the multi-layer steel MLS. Both have a 84.0 mm bore and differ only in thickness, 1.3 or 1.6 mm. 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

Gasket volume is the room it leaves free above each cylinder. It adds to the combustion chamber and lowers the compression ratio; as both part numbers share the same bore, the 1.6 mm gasket lowers the ratio more than the 1.3 mm one.

Preparation and fitting

Before reassembly, check the flatness of the head and block faces with a straightedge and have them machined flat if needed. The Athena gasket comes with its coating: do not put any sealant on it.

Technical guide

The construction offered

Athena MLS A stack of two to five AISI 301 stainless steel sheets, laser cut, pressed and then riveted. Around each cylinder, a folded sheet, the Gas Stopper, directs the clamping force onto the combustion chamber; raised reliefs separate the water and oil passages. Two coatings cover the faces: one withstands heat and fills small flaws in the block and head, the other, in silicone, stops the gasket sticking at removal. It is Athena's all-steel answer, from a prepared naturally aspirated engine to moderate forced induction.

Choosing bore and thickness

Gasket bore. The Athena MLS is offered in 84.0 mm only (338399R and 338400R).

Thickness. Peugeot and Citroën do not state the thickness of the original gasket. A thicker gasket enlarges the combustion chamber and lowers the compression ratio; a thinner one reduces it and raises the ratio.

As the original thickness is not published, use a dial gauge to measure how far the pistons stand proud of the block face, especially if you are aiming at 1.3 mm: that figure fixes the distance left between piston and head.

The brand

Athena S.p.A. is an Italian firm specialising in gaskets and engine sealing parts. Its head office and main factory are in Alonte, in the Veneto, with further sites in Spain, the United States, Brazil and India. Car manufacturers fit its multi-layer gaskets as original equipment, and its competition range is designed and built in Italy.

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 bore size of the original gasket, which Peugeot and Citroën do not publish 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: 0209.L3.

Important: these two part numbers are reserved for the engines XU9J4, XU9J4Z and 159K: check your car's engine code before ordering.

Why switch to a reinforced gasket?

When the original gasket reaches its limits, the reinforced gasket steps in: under higher combustion pressure, it holds its thickness and shape instead of being crushed.

Turbo, supercharger or raised compression ratio: the more power rises, the more the head gasket becomes the weak link of the top end. The reinforced gasket avoids the leak, and the head removal it forces, far costlier than the gasket itself.