I don’t have a DB601 handy to compare, but I can say that the only difference I can see between a DB605 & a Ha40 is that the accessory drive gear on the DB is thicker by about 10mm… diameter, number of teeth etc is the same though. I know the DB605 is of greater capacity, but externally & internally (visually) everything is the same.

Also, as 43-2195 mentions, I recall reading somewhere that there was a lubrication issue with the Ha40/Atsuta (am thinking valve gear?) that was caused by an undersight during the licenced production by the Japanese? I’ve also read that the Ha40 was a more reliable engine that the Aichi Atsuta, as the Kawasaki tolerances were better, but some Japanese engines suffered crankshaft failures due to bearing tolerance issues?… not sure if this was both engines or just the Atsuta’s?

Both the DB’s & Japanese engines use the same externally fine splined nuts (as opposed to common single hex nuts) to retain their main & conrod big end caps, so unless one has the correct tools it’s practically impossible to disassemble them without damaging the nuts (which of course wouldn’t be done). Also, having correct tools machined up is not as simple as it may sound… I’d be very interested to know what people working on DB’s around the world are doing for tooling?

Anyway… interesting thread on a VERY interesting engine!