My 1949 HRD C has straight seat brackets, i have read somewhere recently that there where 200ish C RFM's made before the change to the curved bracket. I assumed that the curved bracket allowed the original jig to be used for welding both B and C RFM, but I was told that the straight bracket on the longer RFM, had an adverse effect on pillion comfort and the curved bracket restored the original rate of seat movement and pillion comfort.
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- Thread starter vince998
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I don't know if it was jig or comfort considerations that dictated the seat bracket change but geometry changes putting the RFM seat mounting closer to the rear wheel spindle reduces the benefit the pillion passenger will get from the suspension.
And just to throw some more mud into the water; some of you will know that I have the works prototype Black Knight. This has late 'C' crank cases and a modified 'C' RFM. They were making bikes in times that were difficult both financially and with regards to engineering supplies and my guess is that they just had to use whatever was available at the time.
Norman, by late "C" crankcases I assume you mean die-cast ones. That's what "D" ones are surely? In what way was the RFM changed to suit a "D"?
Mono-Shock, fully sprung seat, no cross bar for the second brake?
Hi Len' there is more to it than just the type of casting. The late 'C's have the boss for the breather outlet banjo whereas the 'D's don't have this bored out but rather drilled to take a bolt to support the 'D' type distributor cowl.. On mine the casting is there but plugged. The rear frame member has not only the castings for the brake cross shaft but these have been machined but not used while the top, which on a 'C' would take the two springs plus damper, has not been made to take that but rather has the 'D' type monoshock arrangement. Remember that the works had already developed this part of the system to be used on he Vincent three wheeler. On that there was a monoshock but interfaced at the front into the rear of a modified 'C' type oil tank. On the fully developed 'D's there is a hollow item brazed (?) into the top tube of the RFM to take the prop which holds up the rear cowl. On mine this is a piece of tube,welded or brazed, onto the top of the rear tube to take this prop. It is clearly a 'C' type RFM but modified during manufacture to take the monoshock and the prop for the cowl. The support for the front of the chain guard is also different 'C' to 'D'. The bracket on the exhaust side of the bike which on the fully developed 'D' is a one piece steel item on mine was a fabricated part made from part of an aluminium 'C' type rear foot rest plate and a steel rear brake torque arm. The dual seat had a very roughly developed steel base, welded up to shape. I have kept the latter two items but fitted the later adopted items to ensure reliability. In case it is thought that these could all have been the work of a private owner doing his own mods perhaps I should say that I have the original log book which shows that the bike was used by Vincents for one year and I also have a record of who owned the bike before me and he was not the man to do any of this work.