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The 850 Commando Frame # Mystery
Dave Comeau  Jan 2001 Updated  25 Feb 2007

In pursuit of information concerning the fitment of a fastback tail section on late model frames with wide loops. I have tried to find a pattern, but so far have been unsucessful. There are both wide and narrow loop late frames. The Italian frames are easy to detect with the small frame tubes being 25mm and the large backbone at 60mm. The British frames are imperial sized tubing 1" and 2-1/4" backbone.

1. VIN- the traditional Norton VIN number on the aluminum plate, engine and transmission note on vin 30xxxx are 1973 31xxxx are 1974 325xxx are 1975-end
2. MFG date stamped on the plate.
3. Frame Batch Sequence number (my term)    #850#F.........#     #=circle with 2 horizontal bars.
4.  Rear frame loop width. Normal 6 3/4" (will accept fastback tailsection), Wide 7 3/8". Measured between the frame rail tubes 4" forward of the rear of the rear frame loop.
5. Letter size as stamped on the aluminum plate and frame batch sequence # . Small 5/32" or big 1/4"(like on engine).
6. Dash or No Dash in frame part number located between the 06 and the 4140 (73), 5404 (74) and 5632 (75E-Start) on the front of the left front tank mount.
7. The aluminum VIN plate is mounted more to  the Left or Right side of the frame neck.
8. The coil bracket mount hole on the tank mount are ROUND or short "slots" with a rounded front and rear ends.

VIN MFG DATE Frame Batch sequence # LOOP N/W S/B dash/nodash L/R rd/slot
302591 Apr-73 #850#F 00108# W        
309911 Nov-73 #850#F102329# W        
313761 Mar-74 #850#F106144# W sm nd R rd?
317462 Jul-74 #850#F107671# N sm d L rd
325545 Nov-74 #850#F125479# ?        
326154 #850#F125517#          
326209 Jan-75 #850#F125681# N sm d L rd
327522 Feb-75 #850#F128153# W        
328348 Feb-75 #850#F128888# W        
329952 Mar-75 #850#F130588# W sm nd R sl
330046 Mar-75 #850#F130370# N sm d L  
330419 Apr-75 #850#F130759# N sm nd R sl
332473 May-75 #850#F332473# N big d L rd
333093 Jun-75 #850#333093#  "no F" W big   R rd

*Starting in may 1975, It appears the VIN was adopted to complete the frame#
If you have any VIN/data contributions for the chart please email me.