How to Restore old hard rubber parts

[tbeiler]

Hey All, just thought I would pass on how I restored old, hard, inflexible rubber parts.
The parts I worked with were the intake boots (carb to head) and air intake boots (air cleaner to carb), on my daughters bike (84 CB650 Nighthawk).
Was considering buying new rubber parts but they are obsolete, so I thought I would give it a shot to try and restore them.
Got this info online.

Use a mixture of methyl salicylate, otherwise known as wintergreen oil and isopropyl alcohol.
Ratio is 1 part wintergreen oil to 3 parts alcohol.
I used a 300 ml container of wintergreen oil and 900 ml of alcohol.
The oil is a bit pricey, $35 Cdn for the 300 ml size, but is 100% pure oil.
The isopropyl alcohol any drugstore will carry, but mine came from Costco, four 500 ml bottles for about $11 Cdn., it was 99% alcohol.

I put the rubber parts into a resealable plastic bags, poured in the mixture, 600 ml per bag, put the bags into a larger Tupperware container and stuffed some rags inside the Tupperware to put pressure on the bags to bring up the level to cover the parts. I only had a finite volume of fluid, 1.2 liters.

Left my parts in for 3 days, although checked them after each day. You could tell they were getting softer and more flexible with time.
After 3 full days, they are much more flexible and shiny. They do like new.
Big note to mention is that this mixture does not swell the rubber parts.

Did see some other methods online like ATF or brake fluid, but these methods apparently swell the rubber.

Got a few more rubber parts in the mixture and will install them in a few days.

Cheers

[Good Hondog]

That's a great tip. Thanks for sharing that trick with us. I've struggled with that same problem restoring old vehicles and trying to save obsolete rubber pieces. What do you think the shelf life would be on that mixture if you kept it in a tightly sealed container? Does the liquid turn black as the rubber parts soak in the mixture?

[tbeiler]

The liquid has not turned black, although there is a little bit of black residue in the bottom of the container.
I did pour the mixture into a tall plastic container with a lid that seals very well to store it.
I will be checking it frequently, since I don’t know if the fluid will eventually affect the plastic.
On second thought storing it in a glass container might make more sense.

Another tip that I recall is to wash the rubber parts with warm water and soap and rinse well, this way
introducing less impurities into the fluid.

Cheers

[dingdong]

Please check back at a later date. I would like to know if the process is long lasting or short lived. Thanks.

[Old Fogey]

If your 'rubber' parts are made of Buna-N (most carb gaskets and oil seal O rings) that mixture will soften them but it WILL expand them too. The secret is to only leave these parts for a few hours at the most and keep a constant check on them.

[tbeiler]

Any carb gaskets and O rings I purchased new from Honda, I wouldn't even bother to try and reuse the old O rings and gaskets. These Honda parts are not expensive and are available.
Restoring parts like the intake boots and especially the boots from air cleaner to carb, since they are no longer available. These boots were hard. Note these are from a 84 CB650 Nighthawk.
It is now mid June, and the parts are still soft and pliable.
I did not see any swelling on my parts.

[Oldbear]

I realize this might not work for the rubber products on bikes but an old hot rodder trick, I have seen work, is to soak the rubber in olive oil. My uncle did this for the door and window seals on his 55 Dodge - which I then did on my 55 Dodge (I know... no originality). I also found a few modern products: Wurth sells an aerosol can of Rubber Care which is great to spray on the door seals when doing maintenance. AC Delco sells a rubber restoration paste (I can't remember the name as it has been over 10 years since I work for a GM dealer). I used the paste on my final drive boot and it didn't explode.