Rebuilding and restoring classic motorcycles is both exciting and rewarding. As any gearhead knows, inspecting, repairing and renovating can be quite the labor of love. Luckily, the following excerpt from How to Rebuild and Restore Classic Japanese Motorcycles can help get you going and aid in your frustrations as it details the beginning steps of the restoration; the inspecting, repairing and renovating the frame of the bike.
Frame
The frame forms the central point to which almost everything on the motorcycle is attached. It must have structural integrity to correctly and safely carry the rider and any passengers from point A to point B, and it must have correct alignment to ensure it travels in a straight line. The removal of all the components from the frame provides the opportunity to perform a careful and thorough inspection of the frame for damage. An initial visual inspection should be performed to identify cracks and obvious damage, such as bent brackets that may have been incurred in small accidents and drops. Cracks in the frame are usually attributed to serious collision damage, abuse, or misadventure while riding.
If you acquire a second-hand motorcycle, have had the opportunity to ride it, and it shows any sign of pulling to the left or right, then sending it to a specialist frame engineer for checking and straightening will be money well spent. If the frame appears to need expert repair, ask the repairer to identify what parts are required to remain on the bike. Often the engine needs to remain in the frame for the straightening process, and the wheels are needed to assist mobility of the motorcycle while it’s in their workshop. Everything else is usually not needed and should be removed for security and safety purposes.
If the ultimate project goal is to build a custom or street fighter, then the bare frame, prior to any repainting or finishing process, provides the opportunity to make any required modifications. If a restoration to factory original condition is desired, then modifications to the frame are to be avoided at all cost. If the frame you have is modified, then the options are either to remove the welded-in bits, or get another frame that is original.
Since most frame and engine numbers are not matched in the factory, this will not be an issue if it is the same model and production year.
Inspection
To perform a visual inspection, look for any cracks on the downtubes and any broken welds at every joint.
The most common failures on a frame are bent steering stop pins, bent blinker brackets, cracks at the front downtubes, and cracked or bent rear shock absorber mounts. Typically, an old frame may also have several patches of rust forming; the most common area is around the battery where acid can leak out or overflow. Often a frame can be twisted slightly enough that visually it still looks fine, but in reality it pulls to the left or right. In this case, it needs to be put into a frame jig and bent back into shape by an expert.
If there is any suspicion surrounding the frame integrity, run a string line down the center and measure from the centerline out to all parts of the frame to determine if anything is amiss. A bent frame may be salvageable if given to a specialist with the right equipment. In most cases they will need the engine and the bike to be a basic rolling frame. All other components (electrical items, headlight, instruments, brakes, front guard, rear taillight, rear guard, seat, etc.) can be removed to reduce disassembly time, reduce any chance of damage, and ultimately reducing costs. The frame engineer will hang the bike by the steering head and check everything from that point. If the frame is bent, hydraulic rams will be used to bend the frame back into alignment. Even a brand new motorcycle can
have bent frames if the quality control at the factory is not up to scratch.
Repair and Renovation
Any frame repair will typically require an expert with the right equipment who specializes in this area of engineering and motorcycle repair. Bending frames back into shape requires a true and accurate jig, and the process of bending the frame requires hydraulic rams positioned at the required points of the frame and attached to the frame jig. It’s not a home engineering task, and you are well advised to spend the money on getting the bike checked professionally; tire wear and the position of the front and rear guards will give visual clues as to the need for frame checking and repair.
Finally, with a frame ready to use the choice of finish must be selected. These days powder coating is an option, but keep in mind that it’s not factory original so extra time and money may need to be spent on a paint job if some degree of originality is sought. If powder coating is your choice of finish, then when you send the frame in you can also send in the other steel frame components, which includes the battery box, mounting brackets, and the like.
These days, you will find that most of the brackets on a modern bike are made of specially machined alloy. There are few steel brackets as the frame, engine, and major items are designed as an integrated assembly to reduce the manufacturing parts count. On the older machines the bulk of brackets are steel plates cut or pressed to shape.
Frame Fittings
In order to fit the bodywork (tank, side covers, etc.), an assortment of brackets is used. Most of these brackets are made of steel and are either welded to the frame or fastened to the frame, usually using zinc-coated steel fasteners. To reduce engine vibration being transmitted to body parts, an array of rubber grommets are often used. Body parts are often rubber mounted to reduce the chance of them dislodging from vibration. Over time these rubber fittings will deteriorate and in most cases they are widely available, so replacement is usually a cost-effective solution. If any rubbers are worn or deteriorated, spend the money and replace them with new ones. If they are cheap, buy extras while you can.
Brackets used to secure the engine to the frame may use bonded rubber to reduce engine vibration and should be replaced if they show any signs of separation between the rubber and steel mounting.
Brackets are also used to hold electrical components, and for items such as blinkers, there are numerous styles of blinker stalks that over time will undergo all kinds of damage. Blinker stalks are often made of die-cast alloy, and it is often more cost effective to replace them than engage an electroplater who can plate die-cast metal. Most blinker stalks are rubber mounted to the frame, and these rubbers will no doubt have worn over time and are candidates for replacement.
They often have an earth strap to provide a good ground for the blinker, so inspection of the electrical connectors at both ends is wise. Damage to these is easy to repair with either a suitable crimp connector (preferably not the standard automotive connectors used in cars) or a soldered joint.
Final Thoughts on Frames
Motorcycle frames from the 1960s to the 1980s were typically spray painted by hand at the factory during the assembly process, as powder coating was not widely used or available in most cities at the time. Paint technology was still evolving, so the type of finish will require some research on your part. If you are aiming to display the bike at “Show and Shine” events, then the frame finish in terms of originality will not be an issue, but judges at a concours bike show may frown upon the wrong finish. Painting the frame to match the original factory finish will earn more points in a concours bike show; the decision is yours.
If you follow the powder-coat route, then Satin Black or Gloss Black are common color finishes used on 1960s and 1970s model motorcycles. To save money and get a consistent finish, all parts that need to be powder coated should be shipped at the same time. Fortunately most of these items are not part of complicated assemblies, so stripping them out of an existing assembly should not present any issues.
It is typical of motorcycles built during the 1980s to have frames constructed of aluminum that were often covered in a silver paint or a clear-coat finish. Few were left bare metal since oxidation would have occurred.
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Everything you need to know to restore or customize your classic Japanese motorcycle.
Whether you want to correctly restore a classic Japanese motorcycle or create a modified, custom build, you need the right information about how to perform the mechanical and cosmetic tasks required to get an old, frequently neglected, and often long-unridden machine back in working order. How to Rebuild and Restore Classic Japanese Motorcycles is your thorough, hands-on manual, covering all the mechanical subsystems that make up a motorcycle. From finding a bike to planning your project to dealing with each mechanical system,How to Rebuild and Restore Classic Japanese Motorcycles includes everything you need to know to get your classic back on the road.
Japanese motorcycles have been the best-selling bikes in the world since the mid-1960s, driven by the “big four”: Honda, Yamaha, Suzuki, and Kawasaki. Of course certain bikes have always had a following – Honda CB750, 305 Hawk, CB400-4, Benly; Suzuki GT750, Katana, GS1000S; Yamaha XS650, RD400 Daytona, TZ; Kawaski H1, H2, Z1R – and these have now become the blue-chip Japanese bikes leading collectors to seek out more common (and now more affordable) alternatives.
This is the perfect book for anyone interested in classic Japanese motorcycles, as well as prepping a bike to build a cafe racer, street tracker, or other custom build.
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