Jason's Chassis: the story
Jason, from Washington State, approached me originally with just a few
questions on how he might make some modifications on an XS650 he bought.
The goal was to get the bike lighter and with better brakes and suspension.
He had a friend in Washington taking care of the motor build, so that part
was being handled elsewhere. Some of what we would be doing was the usual
stuff and some were untried ideas that had been cooking for a while.
left the frame pretty much as is, except for cutting off all original bracketry
and doing some very minor smoothing of some of the cobbed up Japanese machine
I have to mention that in the world of inexperienced bike builders or
first timers, that the simple phrase about cutting off all the un-needed tabs
and mounts etc is easily reduced to a “Phrase”, but in reality
is a ton of work! And an XS650 is about as hard as it gets. Part of that is
because the frame is so simple (and extremely heavy!), that a ton of brackets
have been grafted on over the years. Add to that the developed technique of
removing a welded on appendage without actually gouging the tubing and getting
everything nice and smooth, all the while using tools that get it done quickly
without damage and you end up with a couple days of serious grinding. I usually
try to spread it out over a few days of shorter grinding sessions, lest I lose
So with everything cleaned up and a new seat mount bent up for the XR750 seat,
we were ready for the suspension. At the rear I installed a cromoly rectangular
tube swingarm that was the last one of a batch I had made a couple years back.
To this I added a pair of Works Performance shocks.
Up front was where all
the heavy work was done! I started with a set of 1976 TT500 aluminum triple
clamps and had them bored from 36mm to 38mm to accept a pair of 1990 FZR600
fork legs. Why FZR600? Two reasons. Every pair of forks I get my hands on are
weighed and measured with the stats written on a small chart on the wall of
my shop. For a particular bike I may or may not need a certain length or adjustability,
I may have a weight requirement, stiffness or whatever. On this bike I needed
low weight and a certain length. These forks are the lightest of the light!
Hands down. And they are not so much bigger in diameter that the super light
TT clamps couldn’t be bored to accept them.
Next was an example of Zmurgy’s Law. “Every man has a scheme that
will not work”. My “Scheme” was that we would use an XS650
front hub, FZR600 forks, which would use their stock axle, which would fit the
XS hub and then get a pair of FZR brake rotors on EBAY which would bolt on to
the XS hub and line up perfectly with the stock FZR calipers installed on the
stock fork legs!
This would give us a 99% bolt together set-up with just a few
simple side to side spacing tweaks necessary. That’s when Zmurgy reared
his ugly head. The forks, axle, hub, rotor and spacing were all going together
as planned. But using the EBAY avenue to source the forks, I ended up getting
3 sets before I ended up with a GOOD set. Important tip about EBAY forks and
I’ve been through this many times, is to ask the seller before bidding
if there are any pits, chips or rust or dings in the steel fork tubes. If you
find out there are AFTER you receive the forks, you’ll quickly learn that
they are not usable AND that replacing the steel tubes on your $68.00 purchase
with new $400.00 steel tubes doesn’t make sense.
When I got a good set and had the sliders powdercoated, everything cleaned up with
new seals and fresh oil, got the EBAY calipers purchased and in hand, I then
learned that the spread on the bolt pattern for the caliper lugs changed at some
point from year to year. The calipers didn’t match the sliders that were
all prepped up! Jason opted to install a set of 4-piston Brembos which eliminated
that issue. So I cut up some aluminum and made some adapter brackets.
The wheels were kind of an interesting combo. The front wheel uses a stock hub and a 1979 Special ll Yamaha rim. The rear is a stock aluminum Sportser hub, which isn't near as heavy if you replace the double row rear bearings with quality single row types. It was then laced to a 3.5" x 18" Sun rim.
Both rims were treated to a transparent, black chrome powdercoat and stainless spokes and nipples. The rear brake rotor is from a Buell, carrier made from an old sprocket and a small 2-pot Brembo caliper. After welding up the rear seat loop and taillight bracket, I had to make a new half-round type fork stop to work with the TT clamps. Off to R.W. Little powdercoating for the frame to be coated in dark metallic gray with clear over that.
A quick comment on the seat. Something I always do, but I rarely see others do
is trim the bottom edge of the shell parallel to the seat mount tubing on the
frame or the ground. Nothing looks worse to me than a seat that looks like it
going to fall off the back of the bike or is going uphill. It’s pretty
easy to cut fiberglass and a small amount of effort makes the overall profile
much more attractive!