This report may be interesting for Sunday mechanics and restorers who love old motorcycles and tinkering with them. For those who don't know the fun of tinkering with old motorcycles and have no interest in them, restoring old motorcycles is not something they would expect. However, I would like to show you a part of the restoration process. This is a full restoration of a Yamaha 2-stroke model that was introduced in the early '60s and is now in the vintage category, but it's work like this that adds to the experience.
One-off fabrication by machining
The image in the title shows the "swingarm pivot design style" that is common on large models, but before the early 1960s, some moped 2 models were designed in the same way as large vehicles. With the advent of the Super Cub, the development of new models was driven by the need for efficient production and cost reduction of various parts. Already at that time, moped class models were using a system in which a baked-on rubber damper was press-fitted to the swingarm pivot, and the twisting of the rubber ensured its operability.
This 1962 Yamaha YA5 is currently undergoing a full restoration, and although this model was designed as a utility vehicle and commercial vehicle, it was also a model for riders who preferred the "sport touring" category. Perhaps because of this background, the components of this model's body show glimpses of the development of the machine that was known as the "handling Yamaha" at the time.
When I finished painting the body, I couldn't get the swingarm pivot bushing. The pivot bushing is made of black plastic called "DURACON".
A lathe is used to cut the bars.
By clamping DURACON purchased on the web to the chuck of the lathe and applying the cutting tool to the rotating material, it is "lathe processing" to cut out the desired dimensions. Although the appearance and the cutting materials are different, the swingarm pivot bushing was cut and manufactured in the same way as the wooden handicraft "Wooden Dolls" are cut and manufactured. I myself used to love riding motorcycles, but now I love tinkering with motorcycles and practicing maintenance, and I'm building up my garage facilities. Nowadays, there are more and more experienced riders like me, and if you can secure your own garage space, you can buy all kinds of general-purpose machine tools for making parts. If you have the budget to buy a new large motorcycle, you should be able to buy a power supply (200V), a used general-purpose lathe, a used general-purpose milling machine, an air compressor, and other equipment.
The collar operates inside the plastic pivot bushing, and there must be no rattle in this sliding part. After press fitting, the inner diameter was machined to ensure smooth operation. The outer diameter of the machined bushing must be a few hundredths of a millimeter thicker than the diameter of the swingarm hole because the bushing is press-fit into the swingarm hole. This is the finished bushing and the metal collar (an OEM Yamaha part) that operates inside the bushing. A grease reservoir is spirally machined around the circumference of the collar.
Press-fit fixation is strengthened with the use of adhesives
When the pivot bushings are press-fitted, a strong adhesive is used in conjunction with the bushings to improve slippage and to ensure a secure fit after drying. If the press-fit tolerances are correct, the bushings will not turn or come loose while driving. However, there is another reason to use the adhesive. There is one more reason to use adhesive in this case, and that is to make the bushing slippery during press-fitting. If you have ever press-fitted an oil seal into an engine, you will understand that this adhesive improves the sliding property between the resin and the metal, and makes it possible to press-fit smoothly. The best way to press-fit the seal is not to hit it with a hammer but to use a large vise to hold the parts together and close the vise as shown in the picture above.
The collar rotates smoothly without rattling
After press fitting the bushing, let's insert the collar. If there is any rattle at this time, it is a failure of bush making. On the other hand, if the collar cannot be inserted, it may be due to a mistake in setting the bore tolerance. If you need to make a slight dimensional adjustment, it is better to use a reamer that can make a slight dimensional adjustment called an adjustable reamer.
Cap and O-ring to prevent grease escape
Grease must be pushed in periodically with a special gun from the grease nipple attached to the pivot shaft to improve the lubrication of the collar and bushing. The cap washers and O-rings that seal the left and right pivots, respectively, keep the grease from flowing out. If these O-rings are broken or worn out, they cannot hold the grease. All of the metal parts such as the cap washers are re-unichromed for a clean finish. This is the best part of full restoration.
- Point 1 - Parts that are not available can be modified to be used by diverting OEM parts for other models or by processing.
- Point 2 - Swingarm pivot bushings and self-lubricating DURACON and gunmetal materials can be machined from metal to make your own.
- Point 3. Are the parts you made by yourself functioning properly? In this section, we installed the swingarm into the frame and checked for any rattles.
The supply of manufacturer's OEM parts is one-sided in that if 10 years have passed since the production of the subject model was discontinued, discontinued parts will become more prominent. However, in the case of models that are popular and for which the supply of repair parts is considered essential (if the manufacturer itself considers it so), major parts are often supplied even beyond 10 years. There are also examples of after-parts manufacturers, not motorcycle manufacturers, that thoroughly produce and sell parts for specific popular models. However, now that the domestic motorcycle culture has matured, it would not be surprising if there were an "organization that manages the manufacture and sale of parts for old motorcycles" beyond the boundaries of manufacturers, but the reality seems to be that things are not going as planned.
Here, I am making a DIY swingarm pivot bushing which is no longer sold and hard to find (it is a 60 years old model that is no longer sold). If it is a cylindrical bushing or collar, I can make the parts by myself by lathe processing. However, it is not difficult to make the bushing by yourself because there are high-performance desktop lathes that can be used with AC100V household power supply nowadays.
When it comes to moped class practical models, the swingarm pivot is usually equipped with a press-fit rubber bushing and collar. However, when I disassembled this model and proceeded with the full restoration, we noticed that it had been built to a high standard in many areas. The same goes for the internal structure of the front fork and the swingarm pivot that we are reporting here. Common sense would dictate that these are baked-on rubber bushings to cut costs. The Yamaha YA5, however, had a metal collar and bushings that ensured solid operation (the stock parts used Bakelite bushings, which were then called reinforced plastic). This is a full-blown construction that would be unthinkable today.
By tinkering with these old motorcycles, we can find out how the motorcycles were designed and developed in those days. I think it is very meaningful to enjoy tinkering with the old motorcycle as a hobby and to know the development idea at that time.
Full restoration is a world of self-satisfaction
The Yamaha YA5 was developed and marketed at a time when Yamaha only made 2-stroke engine models, and when they were not equipped with the "auto-lube" oil pump, and was a 2-stroke 125cc series model that had its roots in Yamaha's first mass-production model, the YA1, which was called the "Red Dragonfly. The air-cooled 2-stroke engine itself is now an extinct species, but the 2-stroke models of this era were "mixed fuel models" in which engine oil was mixed in with the fuel. Riding on fuel alone would cause the engine to burn out. The YA5 was the first Yamaha mass-produced engine to use the "rotary disc valve intake system" and was the first model to make various other attempts. While the YA5 was a practical commercial vehicle, the YA5 Deluxe sport-touring model came with double seats and whitewall tires as standard equipment.