I’ve done a quick speed read of Bob Fryars’ articles about the design and development of the AEC A410 and A470 engines. There are some 12 pages of very technical information. Without wishing to be too critical of Brian Catchpole, who understandably was very frustrated about constant head gasket failures with his engine he is wrong in one or two of his comments.
Firstly, the A470 was never a “stretched” A410; both sizes of engines were designed as such from scratch, albeit some of the engine was based on an earlier pre-WW2 AEC 6.6 litre engine.
Secondly, much of the head gasket problems started after the switch to unified thread cylinder head studs and bolts, which was all to do with different thread pitches and depth of stud, and quite frankly is too technical for me. However, the switch to unified threads was forced on AEC by the Ministry of Defence (as it is now) that specified unified threads. This also coincided with the switch to DPA distributor type fuel injection pumps, and they had a characteristic, not fully known about or understood at the time, of increasing cylinder pressures under certain operating circumstances. Again all highly technical and way beyond my knowledge of how a diesel engine works.
Lastly for now, Bob Fryars was never too concerned about head gasket failures per se with this engine range. The vast majority were trouble free and gave good service. Interestingly he states that the A410 and A470 were the most profitable engines for AEC that they ever made.
My own comments from personal experience of the AVU470 and AV505, both in service and preservation in lorries. Never had any head gasket issues and couldn’t fault them.