Hi Ruairidh (mainly)

Very interested in your recent posted photos of a set of well used 3 bearing shells. Noticed the centre main is of trimetal Cu Pb with overlay type. The conventional wisdom was/is that these best suited to filtered engines and/or hardened cranks, but anything is better than the overloaded wm of centre bearing, and the example has fared reasonably well. Is it the material now commonly provided for this bearing or was this a special assembly?
Had the particular engine suffered a lubrication failure or simply done very many hard miles?
Other than after lubrication failure, do you commonly encounter shells failed by major loss of metal as these or do they normally just develop clearance and become audible? In autos generally, thin layer shells are supposed to far outlast poured bearings, which in a Seven have very long life in normal use. Yet you have observed previously that Seven shells tend to be shorter lived.
Perhaps the non pressure system renders clearances more audible?
Bob Culver

Location: Auckland