TOPIC:

1981 KZ650-CSR with re-painted rectangular master cylinder w sight glass

Can the sight glass & its gasket withstand the heat of an oven? I repainted the mc & plan on baking it to cure the paint.
Whenever baking parts, I typically cook them for about 20 mins at the lowest oven temp, then raise the temp to around 225 to 250^o for about 30 mins or so. Thanks.

Hey Marty, I like the baking idea! But maybe as low as it goes! Don't bother upping the temp like the cans say.
Too late to take sight glass out? Break it, buy a new one. That's the right way,
My way would have been to heli-arc up the aluminum reservoir sight glass solid.
I have always used silicone brake fluid DOT 5 for over 30 years. My old Harley has a front master cylinder painted with dupont single stage urethane for over 20 years. Silicone Brake Fluid! Does not eat paint!! It is tough in this cheap ass chicomm produced materials! Take D/L products sorry! All your rubber O-rings, brake seals, petcock seals, they all suck.
So if anyone converts over to DOT 5 Silicone brake fluid. Make sure your rubber O-rings and rubber and seal items do hold up to silicone brake fluid. Mine is purple, I poured it in, it still looks purple today! silicone fluid does not absorb moisture!!!!!!
And paint last for years! In my conditions under normal use!
Sorry for the rant, just having coffee or 4

I'd use a heat lamp.
Steve

I went ahead & baked it. 170 F for about 30 mins, then 195 F for another 30 minutes. After cooling, everything looks normal.
we'll see after installing it. I'm hoping the sight glass gasket is as tough as the fork cap o-rings. The fork caps were stuck, so I applied heat with a propane torch. I was expecting the o-rings to be ruined, but they were fine & I didn't bother replacing them. If the mc sight glass leaks, I already have a spare Honda CBR500 mc that I plan on installing. I'm just waiting for a new banjo bolt & brake lines. In the mean time I'm curious to see if the stuff I did to the stock mc worked.

Martin.

were you able to finish this project or are there any upgrades?

Yes, refurbish completed & master cylinder installed. no leaks. I used Duplicolor brake caliper paint. That style of rectangular mc is prone to leakage at the cap. The diaphragm mating surfaces become oxidized over time & a hard crusty buildup forms, so those surfaces probably should be thoroughly cleaned whenever the cap is removed or probably at least every couple of years.

I used a brass wire wheel to clean the cap & reservoir where the diaphragm fits. some of the crud was rock hard, so I used an awl to chisel that stuff off, then hit them with a wire wheel again. I honed the piston bore with brass wool wrapped around a nylon brush. the bore was in pretty good condition, but it did have some minor pitting at the bottom.

For easier brake bleeding I installed a Goodridge speed bleeder from Z1Enterprise.com.
The old brake lines were already replaced with Goodridge ss lines a few years ago when I refurbished the Fr br caliper.

paint looks more glossy in pics than in person. I'd say it's more of a low gloss or maybe semi-gloss.




spare 750-4 master cylinder on left for comparison. the oxidation & crud on mine was a lot worse




Fr brake caliper refurbished several years ago. same paint as the mc. baked parts in the oven but at higher temps than the mc.
K&L piston & caliper rebuild kit installed. Goodridge ss brake lines installed w new banjo bolt gaskets.

Really nice work Martin. Tedious as all get out I'm certain, but excellent results.

It was a bit of work. I flushed the system first before removing the mc. This kinda helped to clean out the mc & piston some beforehand. The old brake fluid was overdue for replacement. doh. I mounted a spare set of handlebars to a good bicycle stand, then clamped the mc to the bars so that the reservoir would be level & also a little bit away from the motorcycle. in case I spilled any brake fluid. I covered the tank w a thick towel, a heavy duty trash bag & another thick towel. Something else I did was to elevate the caliper, placing it on top of a dishwasher box. I did this for better access to the bleeder & so that any trapped air could more easily exit the brake lines. The speed bleeder helped a lot. Cleaning the mc before painting wasn't that bad. I didn't prep the surfaces perfectly, but the paint came out pretty good. no complaints.