OK, using the pics from another thread I think I can explan what I think needs to be done. In the first pic below, at point "A" we have the chains crossing each other close enough that they will touch quite a bit of the time. This needs to be eliminated. And, as trplay reported, the chain touches at "C". This also needs to be eliminated.
I am using the standard version Musashi to illustrate what I want because the pic has the white frame. Both versions will benefit from the mod that I suggest. If you will notice, one of the differences in the two versions is that the front idler is farther forward on the short version. This aggravates the cross-over problem, bringing the chains even closer together at point "C".
Looking at the third pic you will see a small area of the headtube just below the frame and above the headset bearing cup. This can be used to locate the clamp to relcate the idler, just like the Terracycle frame clamps. Using a clamp in this location will do two things at once. First, it will lower the return chain so it won't hit the seat frame tube anymore. Second, it will raise the power chain so there is no more cross-over of the two chains. The second pic shows the resultant chain routing in black Sharpie lines.
It all sounds so simple, doesn't it? Well, it's not. Raising the power chain changes the angle of that chain to the der post. That angle is somewhat critical to correct function of the der. Even if the chain stays within the der's cage area, it will still be misaligned with the contours of the cage's side plates, and those contours are what make it shift smoothly and correctly.
What I don't know without getting my hands on one to play with is just how much will that misalignment affect the shifting, and can it be adjusted to compensate? Of course, if I had one of my own, I would make the changes, then cut and reweld the der post to re-establish the correct angle. problem solved.
Question for oldfrt and trplay; is the Mush's boom built like the trike booms, with the index-slotted tube and the same diameter? If so, I believe that a trike boom might give us the correct angle we need (or close enough) to make this mod work.
Oldfrt, if you are game to try this mod, I will use my spare boom and make the idler clamp and use my Terracycle idlers to do this if you will provide the bike. if you like it and want to keep it that way, I will only charge you for the materials. Game? BTW, that third pic is of your bike!
Also, in the third pic I drew a circle where the idler will be moved to, with lines showing where the chain will run. In this lower position, the chain will not hit the seat tube anymore.
I'm sure there are those who will say, "But you are adding one more idler that will crate more drag on the chain". Yes, technically it will, but just how much? Do you think you could feel the difference? Also, using the larger Terracycle idlers to replace that small front idler will help eliminate a tiny bit of drag. Don't forget that I once used FIVE idlers on my trikes to do what I wanted to accomplish, and I never felt any difference in the amount of drag. Four of them were Tarracycle's titanium power idlers with ceramic bearings in them.
