Hi Folks,
After having worked on a few sets of the M1r forks, I thought I would post up some detail on what we found.
The M1R are an interesting fork and a sophisticated set of non cartridge type fork (I consider them damper rod forks).
One of the legs has a rebound adjuster at the bottom and provides both rebound and compression damping. The adjustment range of the rebound damping is quite good as seen on the dyno test below:
The second fork leg has only compression damping and is setup to provide position relative damping which is a harder thing to show on a simple graph:
The compression graph is roughly showing the compression force vs position over the first 2" of travel while the rebound graph shows force vs velocity. While the tests were run with out a spring, it is not practical to do the runs without some effect from the air spring force in the fork. Some educated extrapolation and my choice of what I displayed here minimize this issue.
Damping wise, these forks are not bad for the type. In working on these forks, I feel it is important to respect the engineering and design of the era and not irreversibly change those features. Today, we would not be looking to use a position sensitive damping profile. The total forces made by these forks are somewhat high in compression. we suggest non-destructive methods of reducing the compression fork (namely, using lighter oil).
We have had custom springs wound for this fork that allows replacement of the OEM spring with the full retention of the stock internal parts (including the steel spring guide cup). With this knowledge and the correct spring, we are able to service and tune these forks to be suitable to a specific rider without losing the character that makes these bikes the classics they are.
We found that fork seals are easy to come by but the dust scrapers seem to be unobtanium. We have seals and some additional custom springs in our stock.
