Date: Fri, 14 Aug 1998 20:14:12 -0700
From: Ben English
Herewith is the summary of my investigations into the history of the late 750 Commando, emphasising oil filtration (or lack thereof), based largely on information supplied by participants on both Brit-Iron and the NOC e-mail lists.
I have repeated the manufacture date in the format quoted to me.
Norton may indeed have varied the representation of the month, or my informants
may have altered it. Other codes: "-" means the information is not
expected, "?" means not supplied or not known by my source, and "not present"
means Norton left it out.
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It is my personal opinion that the last number shown was supposed to be either 225036 or 230536, but was mis-transcribed by a management twit distracted by his impending redundancy. But since it is also missing the sump screen, perhaps it is one of a last batch made up of left over parts that missed inclusion in the records.
Roy Bacon's "Norton Twins" mentions the breather change to the crankcase, and states that the oil filter was introduced at the same time, but we know Bacon cannot be trusted to this level of detail.
The commonly available late Commando parts manual covering 850s and 750s "after engine number 212278" shows no sump screen, but shows the oil filter for all models, so perhaps factory installation of the oil filter began at that that number. This speculation is reinforced by the results of the survey. It is interesting that this parts manual reference is the _only_ number in the 210000 series I have come across.
We can probably be sure that factory installation of the external filter on 750s must have begun no later than 220000, as Norton part number 06 4135, the "Commando 750 Riders Manual", specified for machines "from engine number 220000", assumes presence of the filter. Based on the reported evidence the sump screen was returned to the crankcase no later than serial 230000. I further speculate that Norton used that watershed in the numbers to do so.
It is tempting to extend the scope of research to early 850s, to discover if and for how long Norton simultaneously put together 750s without external filters and 850s with. But I will generously leave that pleasure to others. However new information on 750s will gladly be received. When significant additions are made I will re-post a revised document.