How to Fix a Worn-out Rubber Blinker Mount? | Amazingly Satisfied With the Result!

The manufacturer's OEM parts are not supplied forever" because the manufacturer's retention period for OEM parts expires after a certain number of years. As soon as parts are out of stock, these parts are generally discontinued. When you come across a model that you would like to continue riding for a while in the future, you will want to purchase spare parts. One of the most important but often forgotten parts is "rubber & rubber parts". Here, let's try to make a DIY blinker lens mounting rubber, which is worn-out and currently unavailable.

Mounting rubber for worn-out lenses

The rear indicator on Honda's Super Cub C100 series and early body models is designed to tighten the lens directly to the frame. It is obvious that the rubber material used at the time was not good, and there are numerous examples of rubber parts, which are gaskets and packing, that have been torn apart. It is also known that when the motorcycle is driven in the rain, rainwater seeps through the gaps in the frame, causing the metal parts to rust. Is there any way we can do something about such rubber parts? Here, I have tried to duplicate the parts by myself.

Utilizing rubber plates and shoe sole repair material

Generally, I prepared NBR rubber plates that are available for purchase and chemicals that are sold as shoe sole repair rubber. Shoe sole repair chemicals are sold in a wider variety than one might imagine, so the demand for repair may be greater than expected. The one made by SUNSTAR featured shape hardening by boiling. Here, I purchased the SUNSTAR product because I thought I could control the working time, but products that dry naturally were also sold.

Started with making blinker body size stencils

The outline of the metal part that will be the blinker base was transferred to a sheet of copy paper, and a paper pattern was made by adding the dimensional outline of the part that will form a footing to prevent moisture from entering the lens. Since the copy paper was too saggy to be used as a stencil, a PP plastic kraft sheet was cut out to reinforce the copy paper stencil.

PP kraft sheets are used in combination to increase the strength of the stencil paper.

After transferring the pattern size to the copy paper, spray the backside of the patterned paper, which is cut larger than the exact size, with glue spray and adhere it to the kraft sheet when the surface is dry. After confirming that the paper pattern is firmly attached, cut the paper pattern with sharp scissors. Holes for tightening parts and wiring were punched out using a hole punch. When punching out the holes, place a board under the paper pattern and use a hammer to punch out the holes.

Footing fabrication integrated with a lens

Comparison of a worn-out rubber part and a rubber part in the process of fabrication cut out from a rubber board. If I could form a footing with this, I could make a pretty good duplicate part. I attached masking tape to the lenses to facilitate the separation from the indicator lenses after forming the footing, but this work may have been unnecessary.

Making a footing with rubber from shoe sole repair material

The used or broken blade of the hacksaw is shaved off with a disk grinder, and a self-made spatula is used to heap the footing of shoe sole repair rubber. The shoe sole repair rubber is surprisingly hard, and the heaping repair itself was relatively easy. Since it does not harden easily unless it is boiled in hot water, it seems that it can be modified with a spatula until a satisfactory shape is achieved. Once the shape is formed, the part is submerged in a pot of hot water, and the sole repair rubber is boiled at the specified temperature and for the specified time to harden.

Repair materials that harden by "boiling" in hot water

As indicated on the package, the shoe sole repair rubber chemical made by SUNSTAR hardens in 5 minutes of boiling water but does not harden during the work. When I took it out of the pot and touched it with the tip of my fingernail at the time it was about to boil, the surface hardened firmly and I could feel its elasticity. I boiled it in boiling water for 7 to 8 minutes, and it seemed to have hardened sufficiently. Compared to the worn-out OEM parts, these DIY rubber parts look solid. The heaped-up part of the footing and the rubber plate was firmly bonded and could not be easily peeled off.

Rubber spray to improve finish texture

The rubber surface on the foot's edge of the shoe sole repair rubber chemical seems to have a matte finish. If the rubber was molded in a mold, the finished surface would have a certain amount of shine, but this is probably unavoidable. Therefore, I prepared a black rubber spray called PLASTI DIP and sprayed an appropriate amount on the finished rubber parts. I was able to get a semi-glossy finishing on the exposed parts. This kind of DIY duplicated rubber parts would be a good idea.

For specially shaped rubber parts, it is extremely difficult to make a one-off. When a good quality part is procured, a silicon rubber mold is made based on it. By pouring urethane rubber, it is not impossible to make a duplicate part. However, it is a difficult task.

However, if the shape is simple, it is not impossible to duplicate the rubber parts by DIY. A concrete example of such a practice is the DIY blinker base rubber reported here.

The materials used here are commercially available rubber sheets (NBR = acrylonitrile-butadiene rubber, 1 mm and 2 mm thick) and "shoe sole repair rubber," also commercially available. In our world, SUNSTAR is known not only as a manufacturer of toothpaste but also as a manufacturer of sprockets and brake rotors. SUNSTAR also manufactures shoe sole repair rubbers. There are various types of such shoe sole repair rubbers (I tried several types), and in the end, I got the impression that this product, which increases the hardness of rubber by boiling it in hot water, is easy to use. There were black rubber and white rubber products, but I decided to use black rubber here.

After making a pattern and cutting out a rubber plate (using a 2 mm thick plate), integrate the lens with the metal part that holds the indicator bulb. The edge of the lens, which serves as a footing to hold the lens, is molded with shoe sole repair rubber. The soft paste-like rubber is boiled in hot water to harden and maintain its shape. Now that the appearance is matte, the parts are sprayed with rubber spray and completed as a semi-gloss finishing. I found that it is relatively easy to make such a flat rubber part by ourselves. Although the shape is clearly different from that of the genuine parts, I was still able to create a functional and satisfactory part by myself.

See Accessories of SUNSTAR
See HONDA Moto Index Page
See Accessories for HONDA SUPER CUB 100 (C100)