At some point, virtually all Minis engines will need a rebuild including many that have previously been rebuilt. A lot of Minis receive a full engine overhaul when they are restored, others because a lot of time has passed since they last had a rebuild; and of course, a large proportion of engines receive a rebuild and upgrade at the same time.
As a general rule, a like-for-like standard rebuild will be fairly straightforward. The wearing surfaces are checked and refaced/reground/replaced where necessary and everything can then be reassembled. It is when components such as the head or block are replaced with used items, as well as when performance-improving modifications are being carried out, that more checks, adjustments and additional replacements will be needed. Consequently, the engineering workload increases.
Of course, even completely standard rebuilds will benefit from some upgrading. The most obvious improvements that come to mind are Tufftriding of the crank and balancing of all the rotating and associated moving components. Invisible mods such as balancing will(CR) being unachievable. In most cases though, changes can be made to other components to overcome the issue. The CR is calculated by measuring the piston deck height and calculating the volume, adding the piston dish volume and the volume of the compressed thickness of the head gasket, making an allowance for the area (the land) above the top ring of the piston and then adding the cylinder head combustion chamber volume.
