Well, while work life isnt exactly boring, it is rather unexciting... So I figured Id blog about the fun-stuff :)
Project is to modify a Single Sided Swing-Arm from a 2006 Honda VFR800 to fit onto an unmodified 2002 Suzuki SV650 frame.
I have the Suzuki bike, and I have the Honda Swing-arm... Now to bring them together!
The trick here is that the new rear whell is 20mm wider than the original, and that makes all sorts of realignment and fitting issues!
I got some tools together, and managed to take the back-end of the subject bike apart on the weekend. And once I had it all apart, I could set about trying to figure out if Ill be able to get the alternate back-end onto the bike in place of the original.
So, I got my trusty steel rule, and a straight edge and I started to measure all the components so that I could see what had to be done...
First and simplest measurement was the inside frame "opening" width of the bike at the swing-arm pivot (135mm), and the outside width of the pivot on the swing-arm (183mm).
... That means that the new swing-arm is 48mm too wide!
And that means that I have to reduce this width by an equal 24mm on each side of the swing-arm (If I dont do it equally then the rear wheel will run "off-centre"!).
... Wow, thats a lot!
Hmm... Well, my initial plan was to machine the bearing sockets deeper on each side of the swing-arm "yoke" style pivots, but there simply isnt anywhere near enough metal for that idea to work!
So, my new plan is to "cut and weld" instead.
So, Ill carefully cut-off the "free" side of the swing-arm pivot "yoke" (where it branches off the main side of the swing arm), and then remove the 24mm from the inside "cut" end of the removed piece; And then re-attach it to the swing arm by welding it (need skilled Aluminium welder to do this job). The other side of the swing-arm yoke will be used as an alignment jig by running the pivot bolt through the attached and unattached bearings :)
Then, Ill cut off the main side of the pivot "yoke" (about 100mm back from the pivot), and then reweld it back on but 24mm closer in to the centre-line of the yoke (using the same alignment jig trick with the already reattached other side of the yoke).
Then Ill have what amounts to a "majorly mis-aligned butt-joint" in the main load bearing section of the swing-arm!!
Needless to say, I will then need to add some serious "bracket" plates of Aluminium to reinforce the joint... Again, Ill need a professional to do this - Whom I have already located :)))
The old "square" and boring (but eminently effective) swing-arm above, and the new "curvy" one below.
The new swing arm as it is now with "cut-lines" indicated...
And a "photo-shopped" version of how it will hopefully look after the cutts and welds :)
OK, so that will get the new swing-arm to fit into the bike frame with the rear wheel centre-line on the centre-line of the bike!
But thats just the start of the fun!... Now, I have to get the chain to align between the front and rear sprockets... And that, is gonna be really tricky and is what Ive been carefully measuring things for...
Here are all the associated measurements:
For the Motorbike and old swing-arm:
Left Side Frame Pivot Hub face to Frame inside left face - 10mm
Front Sprocket Drive-Shaft face to Pivot Hub face - 18mm
Front Sprocket width - 6mm
Chain width (SV650 525 chain) - 22mm
Chain centre-line at Old Swing-arm pivot - 10mm inside of left side pivot face
For the new swing-arm:
Chain centre-line at New Swing-arm pivot - 20mm inside of left side pivot face
Chain centre-line clearance to left edge of rear tire - 29mm
Rear sprocket width 8mm
Now, Im pretty sure that all that will mean absolutely nothing to anyone reading this, but after having drawn myself up a very careful diagram of all the bits on graph paper, the following becomes clear...
... There is not a lot of space!
... And the front chain sprocket on the bike and the rear chain sprocket on the new swing-arm, are mis-aligned by about 18mm!... Which is lots... Which is a bummer!
OK so what can I do about that...
Easiest solution is to make a "tube" extension to the front sprocket to effectively move it further "out" from the bike centre-line... But with the existing sprocket position, there is only about 13mm of clearance between the outside edge of the chain and the inside edge of the bike frame.
And there needs to be about 5mm of clearance to allow for chain slack and flex...
So, the most I can move the front sprocket is about 8-9mm... Which doesnt solve my 18mm mis-alignment!
Hmmmm
OK, so what about the rear sprocket?
Well, I could do the same "tube" extension there but its a much larger sprocket diameter and it gets harder to do (and I think less mechanically sound too)...
But, if I measured correctly, I have 29mm of available space to the edge of the tire... But the tire is a LOT more flexible than the chain and when the bike is cornering, Im sure that inside edge moves by between 10-20mm!... So, realistically, I can only move it 8-9mm before I get into trouble... And, again, that does not solve my 18mm mis-alignment problem...
Hmmmm
But, as you have likely noticed, If I make the "acceptable" modifications to both the front AND rear sprocket positions, we get pretty much exactly the required re-alignment change! :)))
... And, the rear sprocket modification can be made without the difficult "tube" extension too... The rear sprocket width is 8mm... And I need to move the alignment inward by 8-9mm...
So, the simple solution is to machine off the "teeth" of an old sprocket and mount it as normal to the rear hub. Then, machine out the centre of a new (and slightly larger diameter - more teeth) rear sprocket to "clear" the wheel hub, and then drill and bolt it to the "inside" of the old sprocket disk... This will move the new sprocket by the exact 8mm requirement, and will also be strong and simple to construct :))
So, thats the chain alignment solution.
And the only other issue remaining, should be the suspension linkage...
... There is an attachment point on the bottom side of each of the swing-arms for the rear shock-absorber.
Needless to say, the two swing-arms have different attachment points...
So, again, this will require cutting and welding, but I think its pretty straight forward since I can simply cut the mount off the old swing-arm and weld it onto the new swing-arm in the correct location (after cutting the old mount off of that swing-arm too). Note again that professional welding skills are required here since this linkage point takes the full force of all rear wheel suspension forces... And the forces are amplified by the long swing-arm lever-arm and the short shock-absorber lever-arm... hmmm Need to add some reinforcing too!
Old and new swing-arm suspension linkage pointsBut, after having "done the math!", I now feel that I will be able to make it all work without too much expense or "precission machining/engineering"
... So now Im gonna commit to "start cutting" and we'll see how it looks after I get the modified swing-arm back. Then Ill fit it to the bike and do another careful re-measurement to confirm exactly what I need done to each of the sprockets.
Stay tuned for the next update on my SV650 Single Sided Swing-Arm Conversion :)))
