New MLS Head Gasket from XPart

An interesting development we were informed of during our visit to XPart was the new MLS gasket - seen here, pictured below. Part Number ZUA000080, the new gasket set consists of a steel gasket consisting of 5 layers. In the centre is a steel shim with swaged on fire rings - which appears to be very similar to the original gasket designs.

These layers are there to help prevent any coolant leakage failures - which, on the older gasket design, was frequently due to peel-away of the butyl rings.

This, like the original gasket is encased by two steel layers - rather like a sandwich. However, in contrast to the older gasket design, rather than using bonded-on 'elastomeric' butyl rings to contain the coolant jacket and oil drain spaces, the gasket has an additional two steel layers on either side of the gasket with swaged / raised areas to provide the coolant/oil void sealing (the gloss-black layer just visible in the image opposite).

The other interesting feature of the new gasket set is the so-called 'sixth layer' or shim. The shim, as shown opposite (left), is inserted between the MLS gasket and the cylinder head, black surface uppermost. The shim is coated on both sides: on the upper side (the head-facing side) with a dry sealant (it has the same black, glossy appearance to the gasket face opposite) and the lower side is coated with an inert matt-grey treatment - and it is this side of the shim that comes into contact with the upper surface of the MLS gasket.

The shim appears to provide two main roles. Firstly it prevents the fire rings on the gasket digging into the cylinder head. When the head is torqued down, the fire rings are crushed between the liners and the cylinder head. The shim prevents the ring from digging into the head, and enables the 'ring to roll over the gasket layer in the manner in which it was designed.

Secondly, and the potential advantage of this system over the original gasket design, it acts as a protective layer to the cylinder head, a layer that comes into its own if the condition of the head is less than perfect. Examples of this is where the cylinder head has gone soft, or where the casting has an imperfection close to the combustion chamber; the shim will help prevent the liners hammering into the head in the fashion demonstrated here (although it has to be said that when the head becomes as damaged as the example shown, the shim will merely delay failure, not prevent it) or aid in sealing the fire walls.

New bottom end oil ladder
As part of the MLS gasket kit, there was another intriguing development - a new lower oil rail. The oil ladder is located underneath the crank bearing ladder at the base of the engine - effectively representing the 'base plate' of the engine, and thus plays a significant role in the stiffness of the assembled engine 'sandwich' as a whole. The engine through-bolts (a.k.a. long or 'stretch' bolts) thread into the oil ladder - which as can be seen on the figure opposite (left) can be viewed if the engine's sump is removed.
Made of 356 alloy rather than LM25 as in the original, the new oil ladder's alloy material has marginally better mechanical properties when compared to the original's LM25 - although, arguably, the practical difference between the two is minimal. Perhaps more significant, is way the way that two ladders are designed. In the image above, the two ladders are pictured in the same orientation - what you see is effectively the same surfaces as you'd see if you removed the engine's sump and viewed the ladder in situ from below. As can be seen, the new ladder (top) is boxed over, whereas the older ladder (bottom) has its strengthening webbing with its face abutting the base of the crank bearing ladder. Moreover, consider the width of the diagonal webbing - it is significantly thicker than that seen on the original oil ladder. Therefore, it would appear to suggest that the new ladder is designed to be far stiffer than the original design. That the new oil ladder also weighs 20% more than the original ,lends further weight (excuse the pun) to the argument that the new ladder is indeed designed with torsional stiffness in mind.

According to the service bulletin that covers the new MLS gasket, the new oil rail MUST be fitted at the same time as the replacement gasket - so it seems likely that the EU IV compliant K-series, had the engine made it to this stage, would have come similarly configured.
The Rover 75 & MG ZT Owners Club Ltd 2006-2023