No expert here but happened to come across this last night while reading about oil.
"PolyEster (RedLine) oils have by far the best performance in extreme high temperatures, and are the preferred oil in old "air- cooled" Nortons. I put "air-cooled" in parenthesis as one could also call these engines "prayer- cooled." The Norton 750 commando will destroy a Group I oil fill in 75 miles on a 100 degree day. No kidding. The Brits really did not understand until about 1990 that some of us live in places where the temperatures get over 80 degrees and cities are more than 10 miles apart. If you love those old British twins, you need to find a good supply for RedLine oil."
http://motorcycleinfo.calsci.com/Oils1.html
the combat engines were the ones that had lower end bearing and oiling problems. Combat engines were higher performance engines than your standard 750 and ran higher compressions and tighter tolerances, which when you combine them with soft roller main bearings is a recipe for disaster. The combat engines would actually flex the crank at the upper rpm ranges due to the higher compression and this would wear out the crank bearings (and occasionally caused crank failure). If you did not beat the engines you could get resaonably high mileage (even by honda standards) out of these engines, but when you beat them they die hard quick deaths. Additionally the stock roller bearings like high sulfur oils as it causes them to last longer by holding more lubricants in the bearings at higher rpms. Additionally the shape of the roller would push oil away from the surface creating points of pressure when the crank was flexing which is where oiling became an issue and the bearing surfaces would score. Non-combat nortons were only slightly more durable as the engines did not have the higher compression so flexed the cranks less. Theri failure is less temprature related as it is materials related, although higher temps would exacerbate the already existing flaws. Really a lot of the issues that people say about nortons are reputation fallout from the "Fragile" 72-73 combat models. Yes they have their issues but if you don't beat them they last. I had a 1972 commando back in the early 1990s and the only problems I had were electrical, mechanically the norton was pretty tough. I had a friend who rode a 1970 commando for over 20 years without a rebuild or major hassle but he was the original owner (too bad he traded it for a sportster three years ago).
Most rebuilt nortons use "superblend" bearings, this is a norton term for the bearing, which are Cylindrical Roller Bearings with a double lipped outer race, single lipped inner race, preferably brass caged, although polyamide cages are becoming more frequent. they have a very slight barrel shape to them. These were installed in nortons post 1972 (I think) so the later ones have a more bulletproof engine than earlier more fragile models.
another problem was that the 1972-73 engines would wet sump at high rpms and cause pressure loss. this was corrected with the 850 engines and you can mod the 750 engines to not have this problem by plugging up the oil scavenge hole in the 750 cases.
commandos make between 65-69 hp depending on model and state of tune. Not a lot until you consider the bikes wet weight is 380 lbs (that is japanese two stroke territory in terms of weight). That is roughtly 5 lbs per hp the bike is carrying, vs our cb750s which lets just say for arguments sake make 68hp and weigh an even 500 lbs, carry about 7 lbs per hp. The three fastest bikes in 1969 were the harley sportster, the norton commando and the cb750 (all held the fastest bike spot depending on what moth it was since they all had different introduction dates), that is pretty good company to keep.
BTW, people built tritons not because the triumph motor is faster, it is because it is more durable.
If the cases are assembled properly the engines themselves do not leak oil. from the bottom end (all bikes leak from the base and head gaskets eventually including our beloved CBs). The biggest leaks come from the tranny which has to seperate places where they use an o-ring where a dedicated seal should have been used. one is behind the clutch which leaks through the primary and makes it look like the engine is leaking, the other is the shift shaft. There are companies out there who can modify your cases to take real seals and this makes them fairly oil tight.
A norton commando has alot of positive points (contrary to bryanj's post) but daily use is not one of them. when I had my 1972 I swore up and down that I would never own another brit bike because the lucas electronics failed me a lot. I even gave up motorcycles for 4 years. But I used that bike as my main means of transportation. Now I have a cb750 and I use that as my daily ride, when the white stuff does not fall from the sky, and I like it. Not because it is a better pleasure motorcycle because it is not, but because it is way more durable. The things I do the my cb750 I could not get away with on a brit bike without the expectation of walking home, but few of those are speed or handeling related. Now that I have the cb it is nice to own another norton again as a pleasure motorcycle because I don't have to rely on it to start in 18 degree wheather in a slight rain (though it could do it). Now that they have japanese electronic kits for the nortons and you can rebuild them to more durable specs you probably can use them as a daily rider with japanese reliability, but the advantage of the honda is it is ready to use out of the box and cheap to replace should you prang it.
