A Way to Soften Up Old Rubber CT90 Motorcycle Parts That Works Well

One of the most frustrating things I have found when working on old CT90's is dealing with the rock and rubber boots at each end of the air cleaner.  When these rubber parts a old, hard, and stiff it can make it a real pain to get in or remove the air cleaner and get access to the carb.  When I first started working on CT90's I found the use of a hair dryer to heat up these rubber parts which made them soften up, but it was only temporary and once they cooled down they became rock hard once again.

I didn't want to buy all new rubber parts for my CT90's as I have too many bikes and I get more enjoyment out of doing things myself and learning about different techniques, so I went on a quest to see if there was a good method to permanently soften old rubber motorcycle parts and I came across the following four YouTube video's:

Video 1 (I really enjoy all of Ichiban's videos), Video 2, Video 3, and Video 4.

After looking at the above videos and actually a lot more, I noticed that one method seemed to be consistently successful and that involved using a mixture of oil of wintergreen and rubbing alcohol. So I decided that would be the method I would use to try and permanently soften the old rubber parts from my CT90's.

At the end of this post I also include a link to a video I have now made on YouTube to share my experience with using this method.

Most people have rubbing alcohol around the house, but oil of wintergreen is not as common, but it is easy to purchase.

If you are not familiar with oil of wintergreen it is a chemical that is actually called Methyl Salicylate and it is worth educating yourself first about the chemical and any potential hazards if you plan on using this method yourself.  I have provided a link here to Wikipedia that provides a nice write-up on Methyl Salicylate.

To purchase oil of wintergreen I went to where I now go for everything else, Amazon.  I purchased a quart size bottle for $26.00 plus shipping which is much more then I needed, but now I have some to use on any future bikes that I buy.  Here is a link at Amazon for the bottle I purchased.

The method I followed was to create a mixture that is one part oil of wintergreen and three parts rubbing alcohol and then soak my parts in the mixture for some number of days depending on how hard the parts were to start with.  At the end of the soak I would rinse the parts well in normal tap water.

I just used an old yogurt container as it worked well to hold enough of the mixture to cover the two rubber boots from a CT90 air cleaner like is shown in the photo below.

I let the parts soak for a number of days and periodically removed them to see the progress and found that it took generally about 1 to 2 days for parts that not overly stiff to start with to almost a week for parts that started off rock hard.  But in the end, the mixture was able to soften any part I put in it.

The one side effect of this process is that there can be swelling of the parts, especially if they are soaked for a significant number of days.  While a the swelling had me a little worried at first, most of the parts shrank back down to close to their initial size after about a week of being out of the mixture.

Here are some shots of the swollen parts next to some yet to be soaked parts just after they were removed from the mixture.

Overall I am very happy with the results I got from using this process and plan on using it on all future bikes I pick up.

I also made a video at the link below that provides a little more insight of how things went as I used this process for the first time and you can see how effective the process is for softening old rubber parts.

I hope this post was helpful and that you find this process using Methyl Salicylate effective in softening your old rubber CT90 parts.

Helpful Links (Shop Manuals, Wire Diagram, Model Information, etc.)

Link to page with listing of CT90 parts available on Amazon