OK, folks. Here's the thing. When it was decided to drop the Combat "option" for the engine (and even the fact of the designation of "option" for the Combat engine is another misnomer in reality), there was an incredibly complicated situation. There were Combat engined Commandos sitting on dealers' showrooms, there were C-Commandos in crates at distributors' facilities, there where C-Commandos in shipping in all sort of situations and that's just the ones that had been dispatched from the factory. At the factory, there were completed C-Commandos in crates ready to ship, C-Commandos off the assembly line but being held (no speeds, handlebar grips, taillamps etc. in stock this week...), C-Commandos that were awaiting rectification after road test, C-engines that had been built but not built into motorcycles, and crates and crates of C-engine parts. WITH to do???
The guiding principle was to be that no more C-engines after the designated serial number would come off the engine assembly line and "every C-Commando that could be touched would be rebuilt". But that left the catching C-Commandos around the world, arranging a warranty-like repairment plan, supplying the correct parts (and that supplying the correct parts would extend from getting parts to the rectification groups within the factory and a correct supply of parts to dealers in Adelaide). The next question was what should those parts be? The process for dealing with the issue of headless pistons was pretty much already underway but what about the compression of heads? Would we take off "C" heads and throw them away and replace them with new standard-machined heads? No, that would have been incredibly expensive so a range of options was tried -- refitting the "C" heads with a thicker headgaskets, fitting spacers under the cylinder bases and keeping the "C" heads, or -- if there was a noted flaw with a "C" head replacing it. There was the question of camshafts -- the double-S camshaft* gave wonderful power for people who wanted that sort of thing and were willing to put up with a wonky powerband -- but they beat the valve train, from tappets all the way to the valves, unmercilessly and there were issues of mis-matched pushrods and heat insulating washers which complicated the already-complicated question of providing training for the technicians who were tasked with rebuilding these engines. In addition, there was a shortage of hands to rebuild engines -- at the factory, at distributors' facilities around the world, and at dealers; this is compounded at the dealer level that by the time we're talking about here, many dealers had their hands full rebuilding failed Combat engines under warranty.
Add to all this, there was the standard situation of "supply-chain". Most dealers knew their clientele -- some had many buyers who were frothing at the mouth over the idea of a hotrod Commando and wouldn't accept anything but a Combat engine; others heard many prospectives say "No way I'm going to buy one with that ratty engine". So distributors were juggling orders from dealers. What do you do if you're a distributor who doesn't have a lot of trained help and you have one red Roadster in stock and you won't get rebuild parts for the dreaded "few days" and a dealer is screaming for an order that's gotta-be-red-Roadster-with-the-Combat-engine? Yep, that motorcycle is going to go out unmodified and will roll out the dealer's shop with little more than good hopes. Same thing applies and the factory -- at this time, motorcycle assembly had been very much reduced at Andover so distribution sales people at Andover had little resource to provide a specific motorcycle for a demanding dealer than to get on the phone with a "we don't have a metalflake blue Roadster in stock but we'll lose a customer is we can't supply soon" to the production schedulers at Wolverhampton. If a blue Roadster was sitting there at Wolverhampton, you can bet that it would be the first motorcycle on the lorry to Andover the next day -- rebuilt or not.
And there were the situations that were the complicated type? What do you do with a motorcycle that has an engine that was among the first few built with Superblends and improved pistons but had the double-S cam and milled head -- there were more than a few like that. Would you change the head gasket, providing lower compression with the "C" head but leave the double-S cam and push it out the door? Speaking of Superblends, it was a very high priority for rebuilt engines to go out with Superblends but especially in the first stages of the rebuild effort, RHP (the long-time Norton supplier of roller main bearings and the originator of the "Superblend" description) could not supply nearly enough replacement bearings in a short period of time. So after a supplier search, it was discovered that the FAG British distributor just down the road in Wombourne could get plenty in a short time (only later was it noticed that the FAG bearings were cheaper and carried a higher dynamic load rating -- although all results seemed to indicate that the RHP bearings were "good enough" to solve the problem in service, it probably didn't make much difference in reality; still, the FAG bearing became to default factory fit and supplier-through-spares bearing, and was also referred forever more as a "Superblend" although FAG never use that description.)
I'm describing all this to demonstrate that there's a "theoretical" Last-Combet-Engine-Built serial number out there and it's important in its own way but in reality there were many serial numbered engines long before that theoretical Last-Combat that rolled out of the dealer's front door without a single Combat part (or maybe only a "C" head with a compression-reducing plate) and a number of completely Combat-stock engines after the Last-Combat that were sold.
With so much "it depends" in the mix, does it really matter when describing a serial number from or just after late Combat-engine production that's been completely rebuilt at least twice in the past 52 years?
And speaking of the double-S cam, many people aren't familiar with the difference between the Norton "SS" cam and the Norton VIlliers double-S cam. I'm not familiar with the development of the double-S cam but it's quite different from the "stock" Commando cam grind. The "SS" cam, pronounced "ess-ess" was developed for the 650SS as a hot-road-sport and racing cam in the late 50s. And it proved to be a good camshaft, if they were competently produced with the correct heat treatment, they were remarkably reliable in service with lots of power that was arranged with a very user-friendly "torquey" powerband. But, I hear you saying, 'what does this have to do with the Combat camshaft?" The answer is that the "SS" camshaft proved to be so good that it was adopted as the stock camshaft for all later 650 Norton twins and also the Atlas -- and it was carried over to the Commando as the stock cam grind! So when a Combat-engine camshaft was being fitted to an engine, it was replacing an "SS" cam (the stock Commando cam) with a "double-S" cam that's different.
(The SSS performance cam was developed soon after the double-S cam; it gave more power with a power band no more tricky than the double-S but turned out to be much gentler on the valve train. It's no wonder that Peter Williams selected the SSS cam to be the basis of his more-fully developed and computer-analyzed PW3 cam. I wonder if the cam and valve train troubles with the Combat engine would have been lessened or avoided by using the triple-S cam in the Combat engine._
