I've replaced the pivot bearings so I could clarify the actual pivot's assembly, as discussed with Miles before:
Miles said:
panurge said:
And yes the bearings for the jackshaft fitted in the head housing..
I got that bit
Is there another bearing for the swingarm on the other side of the head, though?
Than Looking the whole system disassembled I've decided to made some calculation and analysis about an idea I've posted yet:
panurge said:
Another idea should be a BB used as jackshaft (with a big swingarm pivot arrangement around the shell) and then use trial crank-arm's ends (I mean completely sliced arms) as spindle ends + freewheel threads....
And It seems to be doable for a new frame, (2 plates+ 1 swingarm+ 2 retainers+ 1 new seat-tube end and 1spacer)....simply beefing everything until the pivot axle meet a BB shell diameter.....
It will makes the vertical swingarm's element insanely beef, but, save lot of work and money for a new frame project instead of projecting and prototyping a dedicated jackshaft assembly with a more reasonable diameter...It should also cure a bit the pivot flex attitude.
The use of a standard BB shell (standard 73 mm should be perfect) and BB, opens some interesting alternatives:
- Allows to use crucial precision/high-end off the shelf components (a Ti Paragon shell could be perfect http://www.paragonmachineworks.com/cgi-bin/commerce.cgi?preadd=action&key=BB0022
)
- a custom or off the shelf shaft with key or flats for freewheel adapters.
- or a SickBikeParts keyed bb with a sliced/rectified trial right arm end on the left Side and a keyed freewheel adapter + fixed sprocket on the right...(supposing this BB could be reversed)..
- or an ISIS BB with the same config left side and a custom isis splined FW adapter + fixed sprocket to the right that could be made starting from another sliced/CNCed, reversed, right arm end. Onza and Tensile made some useful flat 2d shapes crankarms for this purpose.(http://www.tartybikes.co.uk/cranks_single/tensile_uci_urban_legend_crank_arms/c515p290.html; http://www.tartybikes.co.uk/cranks_pair/onza_zoot_crankset_with_bashring/c514p11433.html), the the typical eccentricity of these parts could be the only problem I see....
With 1.5mm retainer caps (those I have in my hand with the axle), an array of 61809-2RS bearings (45x58x7) could be used around the shell for the swingarm pivoting, than the bb caps itself will acts as bolts to make the swingarm and the BB shell (usually from 1.5" to 42mm OD as in my case) solidly fixed, maybe cups with a larger custom flange will be needed or washers could be enough...Haven't investigated yet, but seems an easily solvable question.
Hope, with the help of pics, that everithing it's clear, anyway, I'll model something and I'll post some sketches soon.
Any kind of comment or advice is welcome...