| Taking the RD400 into the new millennium. The RDZ400
project. I've always liked the RD400s engine, aircooled
simplicity, strong compact design & the fact that you
can double the HP & more if taken to the radical
edge. What has never really inspired great confidence to
me has been the chassis. And with each passing year has
felt even more dated.A dual shock bike in a monoshock
world, A single disc bike in a dual disc world.Something
had to change. Since the RD evolved into the LC & RZ
that seemed the logic first place to look. LC went to
dual disc & monoshock but took a step backwards in
fork diameter & went to rear drum brake, so that
would mean only using the shock & swingarm.In the RZ
YAMAHA fixed those problems, kept the dual disc &
went to a modern upright shock/linkage system. Bingo. What
building the bike came down to was this. putting an RZ
& an RD side by side & supporting them upright.
Keeping the RZ together & working with RZ parts from
another bike is helpful. Measure the angle of the RDs top
frame tube with a level, this is the angle you'll need to
have when it's all done. Install the RZ front end on the
RD which is a straight swap & set the height were you
want it. i.e. I put my clip-ons above the triple clamps.
On the RZ measure the angles of the lower links in
relation to each other & the swingarm, this is the
most important thing that needs to be duplicated on the
RD. If you want to use the thick RZ swingarm pivot side
thrust washers you'll need to pull the bearings &
machine the bearing pockets deeper.if you do it like the
RD (I did) you can press in the bearings to the proper
width & trim the swingarm to the bearings. Narrow the
swingarm pivot tube to just slightly wider. Also narrow
the RZ dust covers to fit. Now that the swingarm fits in
the frame we need to attach the lower mount. On the RZ
this mount comes off a large oval tube below & to the
rear of the engine, were we have a 1" tube on the
RD. To duplicate the oval tube I added a second 1"
tube in front of & up against the first. Install the
swingarm with wheel & set the links to the angles you
measured already. make a cardboard template for brackets
to go from the twintubes to the link mounting bolt
location & cut the brackets out of 3/16" plate.
Weld it all in & bolt it up.For the upper mount put a
1" tube across the rear frame tubes level with the
upper rear engine mount tube. It's a good idea to mock up
the engine & chain at this point & check chain
clearance once you set the upper shock mount location.
Set the bike to the same angle as you measured in the
beginning with the level & make a cardboard template
to connect between the shock (centered so it has good
swingarm clearance), the upper rear engine mount tube
& the new tube. Cut the brackets out of at least
1/8" plate, box in the top of the brackets, weld it
all in & bolt it up.
The only thing remaining is sprocket alignment. you'll
need to check this but it's off by about 3/8". This
can be compensated for by fully offsetting the front or
as I did, use a 520 front sprocket & offset it
1/8" with a spacer (I used a clutch basket washer,
their the right i.d & exactly 1/8") & then
machine 1/4" from the rear sprocket carrier. It's a
little bit of work but you end up with a chassis as
capable as the engine & you can ride your old friend
into the new millennium.
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