Oh no!!
 

Spoke too soon. Left the epoxy in the brake fluid for the rest of the week, and the epoxy started to turn to a clear glop floating in the brake fluid. Looks like I'll have to soak the master cylinders in brake fluid to loosen up the epoxy and start over again. With a different epoxy this time. Any suggestions on type/brand? Something someone has used before?

I think most epoxies are pretty much the same type of thing. If it was me I would bite the bullet and get a new set of masters so I could ride. One thing that could be done is to make a metal plug to cover the hole left by the sight glass and just check it once in a while. But for all the trouble it would take I would still buy new masters. I think they are made of some sort of pot metal or real cheap aluminum castings so solder or welding would be out. john

The little train that could
 

Well here's the deal-e-o guys. When I started this little project, I epoxied in the sight glass. Then got sidetracked. I came back to the master cylinders a couple of weeks later and read JCT's post about compatibility of the glues. I decided to do a test on the epoxy I was using to seal up the sight glass. So I mixed up some and let it set 24 hours per the label to cure. Then I started my compatibility test. Immersed the cured epoxy in brake fluid and let it sit. Well in 3 days the epoxy was a gel sitting in the bottom of the brake fluid. So I figured that epoxy wasn't going to work. Best way to remove said epoxy? Soak in brake fluid! So I put the M/C (and another sight glass I stuck together from a motorcycle I'm working on) in a container of brake fluid. Well after about 2 weeks of soaking, no change in epoxy. Didn't even soften up. The difference was the cure time. So after 3+ weeks of cure time the epoxy is good to go on the sight glass. 24 hrs, no good, 3+ weeks, good. So if anybody is going to use the epoxy listed here, better let is sit and cure more than 24 hours. I used Permatex 5-minute Permapoxy.

JCT: As for getting M/C(s) for riding, it was too cold anyways. I still gotta finish the engine and fuel system first.

Perhaps a large faucet valve washer between 2 steel washers with a screw and nylock nut to hold it all together. Geez, sounds like something I would try lol

I have had to fix at least ten of those over the years and what I do is to pick out all the old plastic "Glass" and then clean the entire window with brake cleaner to remove any trace of brake fluid in the window then I fill the entire window with RTV silicone. Black, Red, Clear, whatever. Then I use a matchbook cover or a putty knife to smooth off the surface in all four axis. N,S, E, W so the window gets sealed well all the way around. A little will ooze through the holes in the metal plate toward the inside of the reservoir. You can smooth it out with a pinky finger or just leave it. I leave it. Then allow the silicone to dry for 24 hours, refill and bleed and you are done. If you want to check the fluid you have to open the reservoir cap.

I suppose you could use RTV to glue a new sight glass in place. The RTV will stand up to brake fluid but it's not easy to keep the job neat.

I've also had a bunch off scooters in the shop that had sight glass that was getting ready to leak/fail due to sun exposure. I smeared a nice coat of RTV over the top of the existing glass.