I have also seen a number of bars that have odd contours. I was working on an old Poulon XXV? Not exactly sure what the model was, but it was a small saw. On the lower portion of the nose it had a flat in it for about 3 inches and runs right up to the sprocket. Without drawing it or a picture it's hard to describe it exactly.
What affect do these shapes have on the saw? Cutting, chain/bar wear, etc.
bullwinkle, yes in cold weather thicker oil, such as 15w40, will cause a lope idle. The oil itself won't cause idle smoke, but the 6.0's had several other issues that would cause smoke at cold start. Our 6.0/VT365's do idle rough when it's cold out, but it doesn't cause any harm you just need to let them run for a bit. The 7.3l/T444E engines as well as our C7's, C9's and C15 CATs also have the same cold start issues as it is common in HEUI injectors. The pressure isn't a problem, it's the viscosity that causes the problem. The viscosity will change the injector timing. Pressure is controlled with a valve on the high pressure oil pump, as long as the ICP (High pressure oil sensor) is working properly, the viscosity won't have much of an affect on pressure at the injector.
I understand what you are saying, and I know that any HEUI engine, 6.0 in particular, have cold start issues. In the 6.0's case it has some other problems, several injector updates and so many software revisions I can't keep tract. Seems like every month Ford has issued some TSB and has a new program out! I can't tell you what the Ford owners manual states as I have never read one. I just use the service manual if there is something I need to look up and we run the same oil in just about all of our diesel equipment. The UOA's, even in cold weather, seem to be fine. Certainly using a thiner oil in the 6.0 will help the cold start idle lope, but it's not necessary and doesn't hurt the engine.
02350024vctd, there aren't really any disadvantages between 5w40 and 15w40. What oil you run depends on several factors like what application, what weather will it be run in, etc. Most, if not all at this point, 5w40 are mostly GPIII base oils, and some are blends of GPIII and PAO or ester so the base oils themselves are much better than many 15w40 oils. If cold weather is an issue then 5w40 is a better choice. I run mostly 15w40 and don't have any problems and always have decent UOA's. Delo 400 is one of the best 15w40's, Schaeffers 15w40 is also an excellent oil. Rotella 5w40, which is a GPIII, is also a good oil. With a B model Cummins, any oil will work as that engine (and it's bigger brother the C model) are very easy on engine oils.