I have two bikes with cottered 3 hole cranks and alloy chainrings. On my 19 59 Witcomb-Simplex is a magistroni chainset with six bolt simplex alloy rin gs attached to a steel simplex adapter which attaches onto the Magistroni c rank. The bcd spacing for this set up is 158. The hole center-hole center i s 79. On my 1952 Automoto ACPS model 30 is a stronglight chainset with six bolt a lloy stronglight chainrings attached to an alloy adapter which attaches ont o the Stronglight cranks. Again, the bcd spacing is 158, and hc-hc 79.
Robert (no 116) St.Cyr
Sacramento/Davis, Ca. USA
> Date: Thu, 2 Aug 2007 12:22:03 -0700> From: jerrymoos@sbcglobal.net> To:
classicrendezvous@bikelist.org> Subject: [CR]6-hole chainrings and alloy ri
ngs for those old cottered steel cranks> > In my investigation of 3-hole ch
ainrings spurred by changing the ratios on my newly rebuilt 1974 Raleigh Co
mpetition with TA Professional, I've come across Stronglight 6-hole 116 BCD
alloy rings. These can be used on 3-arm cranks simply by using half the ho
les. But one then wonders what the extra 3 holes were for. I think TA did m
ake an adapter with a 116 BCD 6-hole bolt circle, but as I've never actuall
y seen one, I have trouble believing all the 6-hole 116 BCD rings out there
, which do show up fairly frequently, were for a fairly obscure TA adapter.
> > I therefore have another theory. As many know, the old steel cottered c
ranks had both rings attached inboard of the arms. Typically a fairly short
bolt would thread directly into threads in the backside of the arms to att
ach a chainring "carrier". The carrier would have holes at a much larger di
ameter, where the rings would attach, either both rings to the carrier, or
the outer ring to the carrier and the inner to the outer. Could the 6-hole
116 BCD alloy rings have originally been designed to upgrade the old cotter
ed steel cranks? It's been observed here before that the best quality steel
crankarms of the 40' and 50's were often not much heavier than newer alloy
arms, which are much thicker. But there would have been a significant weig
ht savings in upgrading the steel rings to alloy ones. So were the 116 BCD
6-hole rings designed to bolt directly to the 116 BCD steel cranks, elimina
ting the carrier?> > But the original bolts designed to secure the carrier
would only be long enough for one chainring. Now the ring manufacturers cou
ld alway have supplied new bolts, and perhaps they did. But an option would
have been to drill another set of holes to attach a 116 BCD inner ring to
the outer one. Was anyone on the list working at a shop in the late 50's/ea
rly 60's, when this type of setup might have been introduced? Anyone have o
r have seen steel cottered cranks with alloy 116 BCD rings?> > Regards,> >
Jerry Moos> Big Spring, TX> > > > > > > --- StripMime Report -- processed M
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