☆Classic Super Cub☆ Eliminate Annoying "Mechanical Noise" Heard at Traffic Lights with Part Replacement

HONDA Trail CT110 Hunter Cub 1981 Semi-Restored Vol. 15

As times change, models in the 125cc class are gaining immense popularity. Among them, the CT125 Hunter Cub's popularity is overwhelming, and many of you may have noticed it frequently seen on the streets. Tracing the history of this series, the CT110 "Hyakuto" series was produced for many years as a long-selling model. This project is about enjoying the restoration and customization of the 1981 model, which was the only one sold domestically. While the appearance has been greatly improved, various problems arose with the engine once it started running...

Finally Tackling Engine Detail Issues...

The horizontal 110cc engine has been beautifully refurbished in appearance, but so far only the valve seats have been cut and the piston rings replaced. Here, we aim to replace key components without a major engine disassembly.

Parts That Were Available During Work Are Increasingly Being Treated as "Obsolete"

Mechanical noise from an engine can have various causes, and the rocker arm that pushes the intake and exhaust valves is one of them. Honda's first-generation horizontal engines are easy to maintain, and the rocker arm can be removed while the engine is still mounted on the bike.

The tappet adjust screw is a part that pushes the valve stem end. In reality, the tip of the adjusting bolt can become unevenly worn, making it impossible to properly adjust the tappet clearance. In this engine's case, uneven wear was causing mechanical noise.

From left: the gear idler and shaft that drive the oil pump, the rubber cam chain idler, and the cam chain tensioner. Compared to the later C65 series engines, the details of this early horizontal engine are distinctive. New parts were purchased.

New rocker arms and tappet adjust screws, new cam chain and cam sprocket. Anticipating that parts would become "obsolete" year by year, all cam drive system parts were replaced with new ones. As a result, the bothersome mechanical noise disappeared.

Cam Chain Area Parts Can Be Replaced Even With the Engine Mounted

By removing the magneto rotor using a special tool, the cam chain and cam chain tensioner unit are exposed on the first-generation horizontal CS90 series engine. The ease of maintenance, allowing the cam chain to be replaced from the outside, is superb. This engine was produced until the 2000s.

The rocker arm can also be removed by removing the head cover and pulling out the rocker shaft, demonstrating excellent maintainability. New rocker arms and tappet adjust screws were replaced with new parts. Oil spray is convenient even in situations like this.

The carburetor was removed along with the manifold, and the work proceeded with the frame secured. By removing the camshaft and the cam chain tensioner assembly, the cam chain can be easily removed. This maintainability is also common to the C65/50/70 series engines.

When restoring the camshaft and setting the cam timing, restoring the flywheel makes the timing marks and lines easier to see, significantly improving workability. The cam sprocket and cam chain remain on the engine side even when the camshaft is removed.

A Self-Made "Locator Sleeve" Does a Good Job

A locator sleeve for the points housing set, machined from an aluminum rod. Without this type of locator, the backup spring of the oil seal lip incorporated into the points housing can come off. This housing structure is somewhat problematic.

By making the diameter of the spark advancer shaft and the oil seal retainer part at the end of the camshaft the same, the oil seal can be inserted smoothly. The backup spring will not come off. If the spring comes off, oil will leak into the points chamber.

Set the locator on the camshaft end, then set the points housing. Once the cover mounting screws are tightened, remove the locator. Following this procedure prevents the oil seal backup spring from coming off. This is a common point of caution for CS90 series engines.

The CT110 Trail features extra-thick spokes designed to handle heavy loads for camping trips. The CT90 to CT110 series did not use the "Hunter Cub" name. For various reasons, that name was not used.

The 1981 CT110 has been finished to handle everything from short rides to camping trips. Compared to when we first received the base vehicle and now, it has been beautifully finished to look like a completely different motorcycle. The saddle-shaped seat, which has become a custom icon, is similar in shape to the genuine CT110 part, but by reupholstering it with the "checkered pattern cover" familiar from the first-generation Monkey, Z50M type, the visual impression of the bike has been dramatically changed. What do you think?

During the finishing stages of the vehicle, the engine received maintenance including valve seat cutting and lapping, and the valve stem seals were replaced. The piston was reused, but only the STD size Φ52mm piston rings were replaced with new ones. The mud-covered crankcase was cleaned with kerosene and brushed. The black cylinder was finished with baked paint, and the cylinder head was sandblasted and glass-bead blasted to bring out the shine of the aluminum surface. The crankcase covers were finished with silver baked paint.

After completing the maintenance of the upper engine, we discovered that the clutch operation was not as expected once we started riding. Smooth gear changes were not possible. Upon disassembling the clutch, we found that the friction discs were worn, and the clutch plates were warped due to burning... Replacing the worn clutch-related parts and springs with new ones enabled satisfactory gear changes.

Shortly after, we started noticing mechanical noise from the engine. Even after adjusting the tappets, the ticking sound wouldn't go away, and the cam chain noise felt significant. Checking the manufacturer's stock of parts at the parts dealer, we found that nearly 20 years have passed since the final model of the same engine series, the MD90, was discontinued, and more engine parts are becoming "obsolete." Therefore, taking this noise repair as an opportunity, we decided to "replace all replaceable parts" in the upper engine. Some "obsolete" parts were already out of stock at the manufacturer, but we found them in circulation and began the work. We replaced the cam chain, cam sprocket, two rocker arms, two tappet adjust screws, cam chain idler gear, cam chain idler, and cam chain tensioner with new parts. With these replacements, we believe we can ride with peace of mind for some time. The cause of the mechanical noise appears to have been uneven wear in the cam chain area and the tappet adjust screws. It's good that it's quiet now!!