updated january 2020
Paioli RSU front forks, as used on Bimotas in the nineties.
Here we have a collection of scanned manuals for the different types of Paioli RSU font forks. In addtions, we have some drawings of the tools used to maintain these forks. The tools can be made your favourite machinist.
The manuals:
RSU41: used on Bimota db2 (Note! 12.9 mb)
RSU43: used on bb1, Mantra, db4 and yb9 (14 mb, Scanned by Riny de Jong).
RSU46: used on SB6, SB6R, SB7, Vdue (4.1 mb)
RSU51: used on YB11. (not yet available)
The tools:
The tool in the image is the tool used to loosen the cartridge from the fork leg on an RSU46. The RSU41 and RSU43 tools look similar (I have a 43mm toolkit), but the dimensions are most likely different. In Paioli's toolkit, there were also other tools, but I think this is the most important one. For seating bushings and seals, the Motion Pro Fork Seal Driver of correct dimension could be a suitable replacement for the original, I presume(?) I have never tried the MP tool on the Paiolis, but I use them on other brands of forks.
RSU41: (no measurements or drawings available).
RSU43: (soon to appear here).
RSU46: as measured by Peter Nisgaard Brink of the Bimota mailing list.
RSU51: (no measurements or drawings available).
Comments on the RSU family of forks:
The Paioli RSU forks has been used on the nineties era Bimotas, and other italian bikes of the same era. The manuals shown above are for the Bimota variants. These forks are a result of Kayaba's cooperation and ownership in Paioli Meccanica.
The former norwegian Bimota importer Jon Oftedahl writes the following abouth these forks, and the spares situation today:
Paioli made 4* different RSU style
forks for Bimota between 1993 and 2000, namely the RSU 41, 43 ,46 and
51. The numbers indicate the dimension of the innertube. These forks
shares a basic design, but as there are some slight differences in the
assembly as well as diffent volumes of fluid and part numbers Paioli and
Bimota came up with a separate workshop manual for each version. You can
use any of these manuals as a guidance when working on your forks once
you
know the differences. It is the RSU 41 that differs most as this fork
has compression and rebound in separate legs. Also the cartridges
(damping assembly) are fixed by an allen bolt from the outside while the
others have internal
treads.
Paioli made specific tool kits for each of these forks. The tools used
for removal of the cartridges and installing the upper bushings and oil
seals are specific for each fork. As the cartridges are of a KYB/Kayaba
design most shops dealing in Japanese brands should be able to help. You
do not have to undo the cartridge to replace oil seals and bushings, but
removing
the cartridge simplifies working on the forks. Also the cartridges
should be periodically removed from the forks for a good cleaning. Just
pumping oil through them while still fitted in the forks is not
sufficient. The internals of any forks will wear. Also oil will age and
water, teflon and metal particles will form a sludge over time and
affect performance. We are not talking about old style damping rod forks
here, but advanced cartridge forks with shims, tiny orifices and
adjustable valves.
I believe that the RSU forks are quite good. Bimota have won several
championships with these forks and what is good enough for racers like
Risitano, Malatesta and Gallaso is good enough for you and me. These
Paioli RSU forks were not cheap to manufacture. The modular design with
a lower leg machined from billet, a separate (cast alloy) axle clamp, an
aluminum
cartridge and the oil seals carried in a "floating" cup shows that
little expence has been spared. But these forks will not perform if
neglected. I firmly believe they are up to the job, especially when
taking into account that they were designed almost 15 years ago. They
may not be in the same league as an modern Öhlins unit. There also have
been some batches (early 46 and 51 units) with production tolerances a
bit on the large side, but a well maintained and correctly set up Paioli
RSU fork will carry you safely both on road and track. It really upsets
me when owners neglect regular maintenance (nor know how to set
them up to suit their riding style) and than moan and groan about the
forks.
Most Bimota owners don't ride their bikes much. You can not expect oil
seals and scrapers to be up to their job after 10 years even if the
odometer shows only 10000 kilometers. Most owners will forget about the
forks untill they start leaking, but that is to late. When they fail to
impress it is cause people think to believe that forks does not wear nor
require any particular maintenance. In fact they are very wrong. If you
have ever seen the internals of a fork after 20-30 thousand kilometers
you'll be amazed by the wear and tear. Most forks will require a total
rebuild if you want original performace retained, a fact that fork
tuners know only to well about. Ask any specialist and he will tell you
that forks should be maintained on a regular basis. If you are using
your bike on a track or pushing it hard on the road the forks may
require a rebuilt every 10000 kilometers. Bimota did
not take lightly on fork maintenance. That is why they made those
overhaul kits. It is a shame that many owners and dealers did not pay
attention.
Regarding oil seals for the RSU 51 (YB11) fork there are no alternatives
except the original (51/10/63) ones made by Kayaba/KYB.
Freudenberg/Simrit (the largest manufacturer in the world of industrial
oil seals) even checked with their competitors. I do not consider
quality problems with the OE oil seals to be the reason for premature
oik leakages, but rather a combination of a batch of RSU 51 forks being
manufactured with large internal tolerances and little use of these
bikes. Silicon grease like DOW 111 works wonders on these seals and help
them not leak first thing in the spring. For those of you that are
looking for alternativ oil seals and think that those for the Marzocchi
50 forks can be used (they are 50/63/10) my advice is not to bother.
They will leak after a few miles. Also there are no alternatives except
original parts for other wear parts like DU bushings and scrapers.
For the RSU 41, 43 and 46 forks parts for the 4 Japanese brands, KTM,
MuZ, Triumph etc can be used. However, the cartridges are spesific for
Bimota.
* Paioli made 3 versions of the RSU 46 forks (the last one being a
hybrid design made for the final version of the Vdue) and 2 versions of
the RSU 51 not counting identical forks except for the spring rate,
lenght of the innertube or colour of the fork legs for Bimota.
Regards
Jon
(former Bimota Norway)
