The K-series engine uses spun-cast iron cylinder liners pressed into the aluminium block casting. Over time and thermal cycles, these liners can settle fractionally within the block, reducing their protrusion above the block deck face. For the original elastomer head gasket, minor liner settlement could be accommodated by the gasket's compliance. The multi-layer steel (MLS) head gasket fitted in the MGOC Spares head gasket kits cannot, the steel construction that makes the MLS seal so durable also means it cannot compress to take up slack at a sunken liner.
If the liners are below specification, the MLS gasket will not seal reliably, and the head gasket work will fail prematurely regardless of how carefully the rest of the job was done.
Measurement and Specification
Cylinder liner protrusion must be measured with the cylinder head removed, using a dial gauge set up on the block deck face. Each of the four liners is checked at multiple points around its circumference, both to confirm absolute protrusion and to verify consistency between cylinders. The minimum protrusion for MLS gasket fitment is 0.1mm (4 thou) above the block face. Equally important, all four liners should protrude by a similar amount, significant variation between cylinders indicates uneven settlement and must be corrected before fitting a new gasket.
Any liner measuring below the minimum protrusion requires shimming before the MLS gasket is fitted. Cases where liners are too sunken to recover with shimming alone remain a reason to fall back to the original-specification elastomer gasket route.
The Shim Set
Cylinder liner shims are precision stainless steel items sized for the K-series liner architecture. They fit between the liner flange and the block seat, lifting each liner by a consistent 4 thou (0.1mm), the standard correction value for most MGF and TF service cases. Fitting a shim requires the liner to be removed from the block, the shim placed on the block seat, and the liner reinstalled, a machine shop operation requiring a press, a clean work environment, and careful technique to ensure the liner returns to its original orientation and to the correct depth. One shim per liner is the specified practice; stacking shims is not recommended.
When the Work Is Done
Liner shimming is typically carried out with the engine off the car or at least with the head removed and the block exposed, this is the only practical time to measure, remove liners, fit shims, and reinstall. Because the work falls naturally within the scope of a head gasket change, the shim set is ordered alongside a head gasket kit on any job where liner measurements indicate correction is needed.
For owners and workshops undertaking a preventive MLS upgrade as a proactive service, having a shim set to hand is sensible contingency, the protrusion check cannot be confirmed until the engine is apart, and being able to complete the work in a single session rather than waiting for parts is a meaningful convenience.