CB900 Chopper project {
I bought the CB900C for two reasons: First, to ride while I fix my Magna... and second, to turn into a bad-ass mean MF'in chopper once the great V-four is running again. It seems the two projects have ended up running in parallel, as I'm reassembling the Magna's motor and doing most of the core CB900 mods at the same time.

Update 4/11/06 As I've been riding my new VFR lately, Chevy has been 'borrowing' the CB and tinkering with it as well. The kickstand has been moved and temporary exhaust has been put on. The devil himself would shreik in fright at the sound of this thing!
I ACTUALLY PUT UP PICTURES!

Frame:

The original frame was used. Any unnecessary pieces of metal have been ground off the frame. There were a lot of accessory mounting pieces on the frame in strange places.
  • (Done) removed the steering lock and turn stopper from the steering neck. The new triple tree didn't mate up with either one. I might weld my own steering stops onto the neck later.
  • (Done) I built a custom fuse box to replace the god-awful beast that used to sit right under the ignition. It's a 4 blade fuse design. I zip-tied it inside the triangle section of the frame, a few inches behind the ignition coils.
  • (Finally Done!) The kickstand has been seriously relocated. A custom mount was made out of angle-iron and welded to the swingarm. Using the upper part of a stock kickstand, a new and VERY LONG kickstand was made from 5/8" solid steel bar. The weight of the bar required more spring tension to hold it up while riding, so the upper perch of the retainer spring was moved off the stock mounting plate and onto the swingarm.
  • (Done) The seat beams (used to support the tank rear and the battery housing originally) are lowered 0.5-1 inch in the front and 3.5-4 inches in the back, with a cross-bar across the rear made of 3/4" 12 gauge steel tube. The frame support for the rear of the tank needs to be supported, but the current bridge-tube gets in the way of the new tank. I'm going to use the same 3/4" 12-gauge tube stock to create a cross-beam just under the existing support tube and weld it up.
  • (Done) A super magna front and rear seat have been used. Because of the electrical relocation and the frame bar changes, no modifications will be needed to the seat itself. It will fit perfectly onto the frame of the CB900. However, I will have to fabricate different metal tabs that bolt from the bottom of the seat to the frame - they need to be wider and a little lower.
  • (Done) The frame cross-member that goes across the top of the rear seat area (above the shock mounts) has been removed. A new rear-section was built, including a teepee-style sissy bar. Solid steel shank reinforcement holds it to the original frame. Tested with a 260lb passenger - the seat was fine, but the rear suspension was another story!
  • Side Covers - I'll be making side covers out of aluminum diamond plate and having them anodized black by a friend who just loves to buy weird stuff like decomissioned military lasers and anodizing tanks. :)
Engine work:

I bought the bike thoroughly used with 60,000 miles and a very recent rebuild. The guy was certainly no master mechanic and didn't rebuild it well at all.
  • Head gasket: The head gasket is leaking pretty bad near cylinder 1. It needs to be replaced.
  • Valve cover gasket, bolts, and bolt seals: I've bought all-new bolts, bolt seals and valve cover gasket. Many bolt holes were stripped and re-tapped with SAE threads and bolts. The valve cover overall leaks like hell, but that'll be fixed when I put in the new stuff.
  • (Done) Carbs: the stock 36mm keihins were pretty spanked. One of the jets is stripped into the carb and can't be removed. I've replaced the carbs with 34mm Mikunis off a '81 Suzuki GS1100E. I had to make custom boots from 1.5" spa/pool hose. I'm going to try to make better boots out of radiator hose- the rubber should grip and seal better. The main jets that came in these carbs were 122.5 and the slows might have been 45. Need a special screwdriver to get to them.
    The low-end power is MUCH better than it was before, but it's still running lean in the top-end. I will probably have to upgrade the jets in order to fix it.
  • (Done) The clutch basket bearings were destroyed. Really destroyed. The clutch would make the most hideous clatter, and shake itself into slipping under heavy load or at high RPM. The bearings have been replaced and the clutch noise is now pretty normal for a 24-year-old bike with a bad basket design :)
Rake and front end:

The CB900 has 28.5 degrees of rake stock. However, the stock triple tree has a negative rake on it! I'm not sure of the number but based on some measurements of high-res photos I'd wager a guess of 3 degrees. This means that the frame itself has a stock rake of about 31.5 degrees. With the lowering of the rear end, I'd estimate that the rake is 33 degrees. By doing measurements of photos, it looks to be just over 33, like 33.2 or 33.3 degrees. The trail is 4.25" (a quarter-inch shorter than stock). I'd like a longer trail, but I don't see a good way to get it other than by raking out the steering neck some more.

  • (Done) I took a triple tree from an '81 Goldwing (39mm forks, 8.4" spread and same neck length, but no rake adjustments). The stock ignition control is mounted straight to it. I'll eventually relocate this to somewhere hidden, either under the tank or seat.
  • (Done) I got the front wheel off an '83 Magna V65 - the same style as the 1983 CB1000C. Real nice looking wheel (compared to the Comstar's)... MUCH better rotors than on the CB. Also needed the V65's speedo gear because of the different rotor mounting stance.
  • (Done) Forks - 1983 Shadow 750 forks... Dual disc, no TRAC, removed air ride (it was optional on the shadows- 0 psi was fine), of course 39mm diameter, my favorite. They have a slightly different look than the stock shocks (no ring grooves on the fork lowers). Like stock, they have the forward-set axle to slightly reduce trail geometry.

    The fork uppers are being replaced with 4" longer tubes and progressive springs. This will raise the front end quite a bit, allowing for better ground clearance and overall evil appearance.
  • (Done) front brake calipers and mounts from a 83 Shadow 750. Reused the stock brake hoses because they're about 1.5" longer than the Shadows'. Used a brake line splitter from a GL1100 because it mounted best to the triple tree.
  • (Done) The V65 Magna axle sits about 2mm inside the forks on the right (it was made for a narrower spread). A stretch, but it works. Spacers had to be fabricated for the axle. The right side went from 27mm to 33mm, and the left side got a new 7mm spacer. All of the bolts for the brake caliper mount plates needed 7mm spacers as well.
  • (Done) Fork brace from a 1200 Goldwing. Perfect fit.
  • (Done) Front fender from an '88 Super Magna.
  • (Done)Stainless Steel brake hoses all around. 40" rear, 23" front master cylinder, 21" to front calipers, plus the length of the joints. I could have probably gotten away with 21" from the master cylinder.
  • (Done)Stainless steel extended clutch cable and stainless tach cable from Barnett Cables. TOP notch work, better than the Motion Pro cables I have.
  • (Done) Turn signals mount directly to the side of my headlight mounting ears (see chopper link below). An old 7in Goldwing headlight sits inbetween. That light is HUGE!
Controls and bars:
  • (Done) 4in Dogbone risers mount up to the bars from an '86 Rebel 450.
  • (Done) I took some controls off a GL1100 or GL1200 (I forget which) that use the same wiring harness as the CB's controls. I had to move two pins on the left control harness to make them work. Since the color coding is the same between the bikes, a quick glance at the old and new control harness made it easy to fix.
  • (Done) a single throttle cable runs down to the carbs.
  • (Done) I have a good master cylinder off a 83 Shadow 750, plus a chrome reservoir cover. A spare (identical) master cylinder from a GL1200 is sitting around in case I need it.
  • (Done) For gauges I'm using these. They're just straight up cool. The electrical for those is run down the center of the steering neck (it's hollow).
  • (Done) I'm using the skull grips from the Chopper link at the bottom of this page. I still need Skull levers like these, but cheaper. Dennis Kirk has the right ones for $20. Skull mirrors (on backorder). See a theme here?
  • (Failed for now) I tried to use a generic throttle to act as a twist-clutch, but the force required to pull the clutch was too much! I haven't given up on the idea yet, but I don't have any great ideas. I might try calling motion Pro to see if they can custom make me a reversed throttle sleeve with a different motion ratio.
  • (Done) I have fabricated forward controls that mount to the front-most engine mount points. I made spacers out of 3/4" steel rod (length 4-3/8") that go from the frame to a 5/16" thick steel plate. 10mm (about 3/8") drilled holes to the frame, 12mm (about 1/2") drilled for the peg bolt.
    The spacers are held in place by 10x160mm 1.25-pitch bolts on the left side and 10x200mm 1.25-pitch bolts on the right (Honda Parts). I had to add about another 5-10mm thread to each of the 200mm bolts. They really only need to be about 180mm long, but Honda doesn't offer any in that size. The part numbers are 95800-10160-00 and 95800-10200-00.
    I have Mapam Restyling Universal Controls that are bolted to the steel plate. The Mapam controls come with two heim joints and two clevis-type joints, tapped to 6.0mm/1.0 pitch. The shifter linkage rod is made from 3/8" rod, and the brake linkage is made of 1/2" rod. The brake linkage lever is made out of the old pedal mount piece, chopped and flattened around a piece of 5/16" plate. This piece has been drilled to allow for the clevis joint to pivot as the brake is pushed.
  • (Done) I am making a suicide shifter for the high/low gear. I'd like to put a big chrome skull on top. I'd also like to put LED's in the eyes that are hooked to the ignition coils, to flash with the spark. In the meantime, the original gear shift lever has been flattened and had the toe cut off. It's hooked up to the high/low and can be 'kicked' into the right gear.
Rear end:
  • (Done) Swingarm - GL1200, which is 4 inches longer than stock. With the swingarm and new front-end, the wheelbase is now 68.75 inches, and it's gonna be longer! ** NOTE **: The driveshaft has a longer thrust out from the swingarm housing on the GL1200. I had to shorten the U-joint by at least 1/4" in order to let the swingarm mount up properly. To play it safe, I cut about 1/2" off the long side and 1/4" off the short side. It was SO close to mounting without the shortening, but I don't trust its behavior during potholes and other heavy load on the rear suspension.
  • (Done) Final drive - GL1200, 2.89:1 versus the 3.08:1 of the CB. Lower RPM for long-distance cruising.
  • (Done) Wheel - GL1200 - 150/90/15 stock.
  • (Redoing) Shocks - Tried 11" short shocks. Too short with the rear seat and sissy bar added. 12.25" shocks from a Suzuki VS750 were the right height when nobody's on the bike, but too soft, causing the tire to rub against the frame during compression. Next I'll be trying shocks from a late-mode HD Dyna. American bike, but Japanese shocks!
  • (Done) Electrical Relocations - I built a custom pan for the battery that lets it hang inside/below the open gap in the swingarm. The electronics have been moved to a folded piece of 26ga sheet metal that mounts across where the stock mud-guard mounts (JUST above the new battery location). Tabs were notched out of the metal to hold the rubber mounting pieces for each device. Once I move the rear brake reservoir, this will clear up space for my seat frame modification.
  • (Done) Sissybar-mount license plate & taillight - For a while I ran a side-mount license plate. I actually hate side-mount plates, but at that point in time I didn't have the rear frame section attached to the bike and needed to get my earbleed fix. The new mount is pretty simple. Just a flat steel plate welded between the two tubes of the sissybar. Light is bolted to it. The license plate is elegantly zip-tied, because the screw-hole width on the plate is a little too wide. Who knows, I might redo the rear frame section to tidy it up.
  • Relocate the rear brake caliper. The Goldwing has a very functional but cosmetically horrible way of mounting the rear brake caliper. There's a wedge-shaped plate that mounts to the axle and the left suspension mount that covers about 1/4 of the wheel. The caliper mounts on the top-rear of this huge, ugly plate. I'd like to put the caliper under the swingarm, if I can provide enough support to mount it there.
  • Fender - IF I end up with a fender at all, it'll be a custom-made fender. It'll be JUST long enough to mount the passenger seat for those times when it's needed.
Soft Tail Mini-Project: - See this awful example of how it might look.

I think I've come up with a workable design to convert the bike to a soft-tail rear suspension, without making any mods to the swingarm! The basic idea is to have a big U-shaped tube that runs from each of the bottom shock mounts forward to just below the seat, then having another tube that comes up and back from the swingarm mount points. The vertical tube would be mounted to the swingarm by having a big circular spacer fit around the circular bearing-holder sections of the swingarm, bushed by a thin strip of rubber all around. The rear bar would be rubber-mounted at the stock mount location. The bars would then be welded together into position, then the centers cut out where they meet, and have two steel plates welded vertically to each side. These two plates would be used to mount the shock, which would be hidden under the seat. The front of the shock would mount similarly between two steel plates coming down from under the rear tank mount, reinforced with one cross-tube between the main frame tubes and possibly also from a tube coming from the seat rails (supporting the tank mount).
Things I need to do:
  • I need to get my hands on some old, nasty shocks to figure out appropriate lengths and potential mounting angles and options.
  • I need to draw up some more detailed diagrams to determine the leverage and force that would be applied to the shock. I might end up needing two shocks under there to support the weight.
Tank:
  • (Arrived, needs modification) The stock tank just sucks. After doing a lot of research I decided on a 1987-1994 Shadow 1100 tank... Here is a picture of the same style tank. It has MUCH nicer curves than the '96+ tanks. Its capacity is 5.0 gallons, over a half-gallon more than stock! It looks GREAT on the bike but it's got a big problem.... the stock petcock location lands RIGHT on top of the left main frame rail. I'm going to build an extension that sticks inwards from the side of the tank (where the CB's stock petcock was) and re-weld it in there. That should be an interesting bit of work.
  • I'll be repairing and painting the tank myself in flat-black, followed by some skull decals (not sure which one(s) yet), then clearcoated. I might get creative and do something strange like silver decals covered by red clearcoat, but at this point I'm far from making a decision. All I know is that there will definitely be flaming skulls!
Exhaust:
  • The bike came with a very rusty Mac 4-1 setup. I took off the can and fitted a downturned tip onto the header for now. It sounds like unholy hell and scares the crap out of anyone who hears me rev it up past 4000 RPM.
  • (Done) I pulled a beautiful set of '93 Nighthawk 750 exhaust pipes off a bike in a junkyard. The airflow characteristics of the header tubes are almost exactly what I was going to have custom fabricated!
    I've cut the downtubes just before the 4-2 junctions, so basically they come down the front of the bike, turn to point toward the rear, and stop before they get to the oil pan. I'm not sure if I like them this short or if I'll make them longer... but I can't make them any longer until I relocate the kickstand. It's seriously in the way.
    I have the downtubes criss-crossed, so cylinders 1 and 2 make an X and cylinders 3 and 4 make an X. It looks really good, leaves tons of room for accessing the oil filter and drain bolt, and leaves the most ground clearance (which isn't saying much!). And yes, they DEFINITELY blow fire.
  • Lengthen the exhaust pipes. Now that the kickstand is out of the way, it's fair game. The biggest problem is finding the right size of ehaust pipe. I'm looking for 1-3/8" OD pipe, with a sidewall no thicker than 1/8". 1/16" would be preferred for weight reasons. In the meantime, Chevy clamped some larger 1-3/4" (I think) tubes around the outside of the pipes and ran them a bit wider. The ground clearance is suicidal, but it sounds like Satan's Pipe Organ when opening up the throttle!
My links thus far:
  • Chopper Stuff for CB750s... plenty of cool stuff here. I already bought most of the stuff I'm putting on, like the skull grips, air filters, headlight ears, ignition mount, etc.
  • Possible CB1000 swappable parts... though for the most part I've found much better alternatives.
  • Rake/Trail equation... This nasty equation is capable of calculating trail, compensating for frame rake, triple tree rake, triple tree forward offset, vertical axle offset, and wheel/tire diameter.
  • A NICE online rake/trail calculator. does everything except vertical axle offsets. Awesome!
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