Vapor Honing For the Win!

Remember my dilemma about that input shaft seal bore? Over the summer, I took the housing with me to visit a couple machine shops and Airhead shops while driving to Connecticut to purchase my 1991 R100 RT. Unfortunately, none of the shops were able to feel confident that the damage could be easily repaired or they were worried about the thickness of the aluminum standing up to the process. They all felt that the part was usable, but recommended using JBWeld or other compounds when installing the seal. I suppose that’s fine for some, but I don’t want to have this in my mind as I am riding the bike. That left the option of finding a used housing or just buying a new one.

All the used housings I could find would need a lot of reconditioning / cleaning and some had other minor damage. They all were priced higher than I was willing to pay, so I opted to just order a new one. Gearbox housing problem solved. That creates the issue that I would have a brand new housing next to a clearly used cover. After many hours of attempting to clean the cover, it was not nearly as good looking as the new one. Even gentle media blasting did not get it quite there. In the end, I decided to find a good vapor honing service to see how that did at restoring the finish.

I have been surprised at how few shops offer this service. Some that do, seem to charge pretty high fees. Given the price of the equipment (I looked into just buying a rig), it makes sense. Vapor honing is not something that is cheap to get into. It requires a good bit of space, huge air compressor, and a fair bit of specialized gear. You build your own setup out of a blasting cabinet, but that’s a side quest that I am not interested in at the moment. I found a guy in my area who is a huge enthusiast and he agreed to take this on.

I dropped off my oil pan, lower steering head, and the gearbox cover for a test. You can see the results of media blasting the cover, which are nice but too flat. I also did not like the overly polished look on the steering head lower clamp, which is common on BMWs. Not sure why that part got more post-casting attention at the factory, but that seems to be the case on most of the airheads I’ve seen. The oil pan has a normal raw cast aluminum finish and will be a good test of what a standard part will look like after vapor honing.

The difference is incredible. These parts look like new, except for the marks showing usage over the past decades. The oil pan is a near dead match for the new gearbox housing, but you can see that the cover is still slightly more dull. It will be close enough for me though.

Here’s a close up of the finish on the inside of the cover.

It’s just fresh aluminum. A great finish. I may have to tear the carbs back down to have them done as well before putting it all back together. Either way, there will be more vapor honing in my projects in the future.