Bill - can you substantiate the assertion that the G15Mk1 was a disaster? I don't think you can - your statement is slander. The nodular iron crankshaft was introduced in 1962 as a result of development work for this engine, making the engine essentially bulletproof from a design point of view. What is true is that all AMC twins suffer of oil starvation to the left side mains - IF and only IF - the owner neglects maintenance. From contemporary and later tests it was reported the G15Mk1 was a strong puller, certainly on par with the T120 Bonneville, and (at least for the second batch w. visual facelift for the 1963 model year) it had pleasing lines too, so it could indeed compete with the Bonneville in the US market as a sportster in the CSR guise.
Well, "ended up" is factually correct, but it wasn't due to G15Mk1 being a failure. As we all know, Norton manufacture and assembly moved to the AMC works in Q1-2 of 1963 as a result of a strict cost-cutting
exercise. Considering the need of reducing operating costs and in view of better sales of Norton bikes in the US (the sales organisation of AMC in the US had been a money-pit with poor results), it was decided to ax the G15Mk1 engine in favour of the Atlas engine. It is a pity this had to be done, because the AMC twin engine is a far more sophisticated design than the Atlas engine, featuring a one-piece crankshaft, central lubrication of mains, a geared camshaft drive, twin camshafts, twin high-capacity oil pumps, short pushrods, and (compared to the Norton) a short stroke, with low wear as a result. True, it would have needed a re-design to enlarge capacity further, but I am sure this could have been accomplished with ease.
Regards,
Knut Sonsteby
