Restoration is one of the most enjoyable activities for old motorcycle enthusiasts. One of the highlights of the process is installing the engine, but whether you are restoring a moped or a large vehicle, you need to be careful not to damage the frame and engine. If the frame has been removed from the moped, you will be surprised at how easy it is to put the frame over the engine.
More caution is required when installing the engine than when disassembling the machine.
This is a 1960s press frame motorcycle that was completely disassembled to repair the swingarm pivot, which was badly stained and rusted. The same is true for the Super Cub, but there are many press-framed motorcycles that have grease and grime built up on the inside of the frame, so removing the swingarm and engine for a partial repaint is often better than degreasing and masking the parts.
Restoring a motorcycle that has been neglected for a long time, or one that has been ridden but treated roughly, is a challenging subject for riders who like to tinker with their motorcycles.
Although it depends on the environment of the storage place, many abandoned motorcycles have a pattern that the upper half of the motorcycle such as the gas tank and the seat are reasonably clean, but the underside of the engine and the area around the footpegs are in a miserable condition due to rust and oil. In particular, motorcycles that have been sprayed with chain oil without being cleaned for chain maintenance often have clay-like oil deposits behind the drive sprocket covers and around the engine mounts.
It is natural to have rust and dirt when disassembling, and it doesn't matter much if the engine hits or rubs against the frame when unloading, but care must be taken when mating the cleaned engine with the repainted finish frame. There are several different types of motorcycle frames, including pressed frames, pipe frames, and even within pipe frames, diamond frames and double cradle frames. And no matter which type it is, the engine is fixed with a few mounting bolts. Therefore, when the engine is mounted, the engine position has to be adjusted more or less to align the mounting bolts with the holes in the mounting brackets.
This adjustment work is done while keeping the engine lifted, so care must be taken, especially when you are working alone. Even if you have a pressed frame with no down tube like the one shown here, you may damage the frame with the engine while adjusting the hole position up and down and front and rear. If it is a double-cradle frame with a four-cylinder engine, even if you think you have carefully cured the down tube with rubber hose and rags, you may be disheartened by "scraping" the frame while adjusting the engine position.
- Point 1: Installing the engine without damaging the cleaned frame requires a more careful approach than when removing it.
If the frame is completely disassembled, the first thing to install is the center stand.
The center stand, which has been cleaned of dirt and rust and repainted with powder coating, is assembled to the frame upside down. Before installing the exhaust system, the stand can be assembled in the raised position, so the pivot shaft of the stand can be inserted without pulling the spring.
The center stand spring on this motorcycle is set in the vertical wall of the press frame, so it is very difficult to pull it out after the engine and swingarm are assembled. If you notice the center stand halfway through assembly, it is better to go back to the frame itself and install the stand.
With the center stand out, the frame is stabilized because it is grounded at 3 points. This makes it easy to temporarily assemble the swingarm.
When mounting the engine to the frame in a restoration project, if you are going to disassemble the frame down to the frame itself, it is a good idea to load the engine before installing the suspension and standing up the motorcycle. This will be explained later, but the center stand should be mounted on the frame before the engine.
Although most motorcycles nowadays have only a side stand, on-road models from the 1980s and earlier were fitted with a center stand as a matter of course. The center stand is mounted below the swingarm pivot and has an extremely strong return spring.
When you try to install the center stand from the frame with the footpegs and engine installed, you will naturally have to put your hand under the body of the motorcycle and pull the spring. This position is very dangerous because it is difficult to apply force to the spring and the spring hooks can easily come off.
The first thing to do is to install the center stand on the frame itself. If your motorcycle has an exhaust system as a stand stopper, you can raise the stand to a higher position and apply the spring at a lower tension position. Also, by installing the center stand first, the frame will be able to stand on its own, making it easier to install the suspension parts.
Some models cannot have the stand installed first due to the position of the engine mount bolt and center stand pivot shaft, but if the engine can be mounted after the stand is installed, it is a good idea to install the center stand first.
- Point 1: When assembling a completely disassembled motorcycle, attach the center stand to the frame first.
A double-cradle frame would put the frame over a transverse engine.
Even with a moped class engine, it can be a challenge to insert the engine mount bolts while lifting from the bottom. If you have a double-cradle frame, lay out a blanket or something to prevent scratching and rolling, and lay the engine on its side.
The engine is placed on top of the frame while checking for interference. In this picture, the bolts are inserted into the mounting holes of the frame, but after checking the approximate position, remove the bolts and reinsert them. When the engine is lifted and mounted, it is necessary to adjust the height of the engine slightly when inserting the second bolt through the first bolt, but it is easy to adjust the height when the engine is covered with a light frame. In the case of this model, the frame was set on the engine on the workbench, the center stand was taken out, the rear wheel was mounted, the stand and rear tire were set upright, and then the front forks were assembled.
If you don't have a frame with undercarriage, it is recommended to put the frame over the engine on the workbench. The reason for this is the difference in weight between the engine and the frame. In many cases, even on single cylinder mopeds, the engine is heavier than the frame itself and requires a lifting motion to be mounted on the frame.
If the engine is placed on a workbench or jack and the frame, which is lighter than the engine, is placed on top of it, it will reduce the burden on the operator's back and make it easier to adjust the position of the engine mount bolts and bracket holes.
In the case of the double cradle frame, the frame can be covered if the engine is rolled over. This is the same method used by motorcycle manufacturers to assemble the body of the motorcycle on the production line, where the frame is placed over the engine, the mounting bolts are inserted, and then the motorcycle is set up for the next process. In this case, the engine is placed in the correct orientation and the other side of the downtube is attached to the engine, then the frame is placed over the engine and the mounting bolts are tightened.
The cylinder head and cylinder of the Kawasaki Z1/Z2 can be attached and detached while still on the frame, so to reduce weight and prevent damage, when the engine is mounted on the frame, only the crankcase is loaded first, and then the cylinder and cylinder head are assembled. With the head and cylinder removed, the overall height of the engine is much lower, making it easier to adjust its position in the frame.
However, for Honda CB750K series, the cylinder head cannot be removed when the engine is on the frame = the engine must be in complete condition when it is mounted. In order to lift the engine with the head attached and fit it in the frame without damaging it, several people have to work from both sides of the engine. On such a model, it is much easier to put the frame over the overturned engine, both in terms of physical strength and psychological pressure.
This method cannot be used when there is no need to remove the undercarriage, but when performing a full restoration, it is effective to change the idea of putting the frame over the engine.
- Point 1: Considering the weight difference between the engine and the frame, it is better to lift the frame and put it over the engine than to lift the engine to prevent damage to the frame and to reduce the burden on the operator's back.
