Yamaha XS650 Chopper/Bobber
Santa Cruz, California

After doing a "rustoration" on a 1977 KZ1000 Police special ( my favorite type of MC), I decided to do a custom chop. Not wanting to make a mjor monetary investment, chopping an old metric bike seemed like a good idea. The XS650 is a simple 2 cylinder that is very durable.

The Yamaha 1981 XS650H was purchased on Craigslist. The bike hadn't been ridden for awhile and was missing the battery and seat. Once I got the bike home and put a battery in it; I was able to start it up and it ran fine. With only 6K on the speedo, it should have lots of life.

The first step was to decide what type of Chopper to make, how far to rake out the front end and how long to extend the back end. I mocked up some drawings in ProE and started planning the bike. I wanted to make the bike long and low, drag style/bobber. The cradle, fork, wheels, and engine are stock. Here are some numbers:

  • 4.5" rear stretch
  • 35 degrees rake (27degrees*)
  • 6.5 Trail (4.53"*)
  • 90.5" Overall length (83.5"*)
  • 64.5" Wheelbase
  • 4" ground clearance (5.3"*)
  • 25" Seat height (31.1"*)
  • 2.5" Seat vertical travel

(* means stock number)

The new xs650 handles ok. It is nice and stable but not too responsive, just what one might expect with 6.5" of trail. The ride with the air shock seat is great. One can take a real hammering with a hardtail but the seat saves your back. Overall, it is quick and lots of fun to ride.

There were some difficulties with the start up. Lost the clutch second time out. It would have helped if I had tightened the camming jam nut on the clutch housing. It had vibrated loose. Apparently a lot of things like to vibrate loose on this bike. The chain chewed up the fender. It took four trims before that issue went away. An ider roller is in the future. Another engine problem cropped up after a high speed run. The bike would start and idle fine, but would completely cut out the second one rolled on the throttle. Well thanks to XS650 Garage USA the problem was solved. The switch box was vibrating so hard it was cracking the welds (Aluminum) and falling apart. This caused the Ignition ground wire to become loose. It took a while to find that one. Still have a minor oil leak at the head gasket and a kick stand mount issue.

The tank and fender will be painted by Crazy Horse Painting, color TBD. I have designed a LED tail light assembly and a LED handlebar turn signal assembly for the bike. These parts will happen in a month or two...or three. This will finish the work for now. Future stuff include: polish/paint hubs and SS spokes,rebuild/paint engine, pretty up the exhaust.

Parts were purchased from MikesXS, a great source for XS650 parts.

Comments/Questions?

Click the thumbnails below for a larger view

Phase I - Disassembly and chop


As Purchased
Right Side View
Left Side View
VIDEOS
xs650 Engine Right Side
xs650 Engine Left Side

                 
       
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Hack saw guide to make the angle cuts for the frame rake
 
This shows the rake with all the cuts.
The top tube is welded together with a lug

                 
       
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The 8 degree rake is the first mod.
The shows the rake with hard tail struts. Rode it around a bit with the struts to get the feel of a hard tail. This is when I decided I had to have a good seat suspension.
The back end is cut off with a sawzall. Lugs are made installed in the bottom tubes.
I use a Thermal Arc Prowave 185 Inverter TIG welder. A great welder for the frame, tank, Aluminum parts, etc.
Decided on a 4.5 inch stretch and 2 inch lower.

                 
       
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The geometry keeps the engine level and gives about 4 inches of clearance
This weld jig worked well for all modifications with and without wheels mounted
Home made tube Bender
Completed Rear End with the stock tank
The fender is off a kz1000 police bike

                 
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Ditched the original tank and decided on a Honda Rebel tank
Rear has a nice profile with Honda tank
It's amazing what you can do in such a small space! Thank goodness for California weather.
 
Tank needed new tank mounts on the frame and tank. The fuel valve was also relocated. After all the welding the tank was pressure checked.

         
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Tank and fender are on. Notice original "70s style pipe with shortly baffle. I like the squared off look of the pipe and it will fit better with forward controls.
Front tank mount with gussets, this frame is going to be strong. No welds were ground.
Close-up of rear tank mount, all custom made with a poly cushion.
Hand made polished SS brake strut.
All components are rubber mounted using stock xs rubber where ever possible

       

Forward Controls Layout

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Brake Assembly Layout  
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All the machine parts were designed and detailed in CAD first. This really helps to visualize and eliminate mistakes

Here is a forward control arm on a rotary table. This was one of the more difficult parts.
The stock folding foot pegs and shifter rubber was used
The rear brake control uses the stock spring and many other stock components. It was tricky to design safe and functional
Both the shifter and bake linkage are fully adjustable

                 
   
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Here is series of shots midway thru the build.
Notice stock pipes and mufflers are installed
Here are the 70's pipes with shorty mufflers
    Here is the mountain bike air shock seat assembly

 
   
Seat Assembly Layout
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This took alot of design to get right. The air shock can be adjusted for the rider's weight and style
The seat is adjustable 3.5" front to back and about 3" vertically
Anyone for 5'3" to 6' 5", 100-250+lbs can ride

       
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Cutting out enough clearance for the chain proved difficult. The fourth trim and weld solved the problem   Had some fun with the kick stand. The mount is a problem. Because the frame is lower and the stock pipes are used, the mount had to be relocated lower than the frame.  
The kick stand bottoms first and is definite weakness.
Finished frame ready for paint and powder coat
       

Phase II - Reassembly


                 
       
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A engine mount was made to remove and install the engine
This mount can be used by one person without dinging up the frame or engine
The frame was powder coated with a black satin finish by S&S Powder Coating, Santa Cruz
Even though most of the welding was done with the engine in the frame, the frame had moved, making for a tight fit on some of the mounting bolts
Never cut and weld your frame without fixing your engine mounts

       
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54 July 2006
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Putting it back together is the fun part
Installed new steering tapered roller bearings
Fabricated a rubber mounted headlight mount for the custom headlight (a freebie)

                 
       
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These were sand blasted, sanded and polished. The process took many hours to complete. See image 28 for original condition
Installed a new sump filter, the original was defective as promised.
Here is series of shots the day of the first ride.
It started up up.
 
                 

                 
       
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Here is one happy guy. It has taken 13 months to get here.                
                 

                 
               
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