Swing arm Conversion Kit, MC28 swing arm to fit MC21
This conversion kit enables you to install an MC28 swing arm complete assembly including, wheel, shock links and brake system on an MC21 without the need to do any machining or modification to the stock components.
The MC21 and MC28 are very similar in a lot of ways especially the frame. The frame geometry on both models is identical and therefore it seems logical that the MC28 swing arm would be an easy conversion which it almost is. For example, either the MC21 or MC28 rear shock can be used (Mounting eyes are the same, as is the length at 304mm). The MC28 suspension linkages line up and the width of the frames at the pivot points are the same. However, Honda chose to increase the pivot shaft diameter which means that the conversion either requires accurate and inconvenient boring of the frame and thread cut to accept the MC28 shaft and adjuster assembly. This would necessitate a complete strip down and risk to the frame as well as making the conversion irreversible. Alternatively, if suitable bushes are used, the MC21 shaft can be used with the MC28 swing arm negating the need to do any expensive machining, or in fact, any machining.
At TYGA, we have made a few of these MC21/28 conversions (two project bikes for example). On the latest project, we spent some time rearranging components from both models and came to a solution that requires only two additional small and relatively inexpensive spacers. We do need to stress though; you do need the Honda parts from the original MC21 and MC28 as shown in the drawing. MC28 parts in dark grey, MC21 parts in light grey and TYGA parts in red. By rearranging components and using the TYGA conversion kit to complete the new assembly, it is a very simple and easy conversion to accomplish. See drawing for how it all goes together. Note that the MC28 parts just stay exactly as they are. The MC21 distance spacer and TYGA part TPER-0067A slides inside the MC28 spacers. Then flip the larger torque arm spacer from the MC21 around to the other side of the torque arm. This of course offsets the torque arm, so we then fit a spacer TPER-0067B between the small end of the torque arm and the engine.
Important: As well as this kit, you need complete swing arm assemblies for both models and the swing arm pivot bolt and nut for the MC21.