Master cylinder repair?

Has anyone tried to repair a the bore of a corroded brake master cylinder with epoxy. I am going to try it by coating the mc bore with epoxy to fill the pits in it and then ream it out to the right inside diameter.
I am talking with the tech people at West Systems Epoxy, but they aren't sure about the compatability with brake fluid. I should find out today.
I bought a new mc off ebay but I can't seem to make it work, too spongy. I suspect it may be too small, 14 mm, although they claimed it to be for a two rotor system. I seem to remember that the oem mc is 5/8, which is close to 16 mm. I will measure my old one before I do anything to it.
Any thoughts or suggestions will be appreciated.
I will report back on whether or not it works. I am going to try it, what have I got to lose?
Robert

Can't tell you anything about the epoxy, just thought I'd warn you that a using 14mm M/C for a two-disc setup is a sure-fire route into your local hospital or morgue. It will feel spongy, and then suddenly lock up. _Do not_ even try to use it, please...
Jeroen

Thanks for the heads up, but why would it lock up?
Robert

mine had a 14mm with double discs on for years and never locked up.

To answer your question about re-doing the bore on a master cylinder, the proper way is to bore it out, then make a sleeve that's a press fit into the now bored cylinder, then hone it to size. Some machinists have a nice little home based business going, doing just that.

Jeesus, Why risk your safty on a tube of freaking epoxy? Or spend the money to have it resleeved? Spend a bit of cash and get the right master that works. Theese bikes are to fast and traffic to dam dangerous to screw around with your brakes. just my opinion. jonnybiker

saltydog wrote:

Thanks for the heads up, but why would it lock up?
Robert

Hi Robert,

They will lock up because of lack of "feel" in the brake lever. This site has a very handy chart to check for the best M/C-Caliper ratio: www.vintagebrake.com/mastercylinder.htm

Jeroen

PS: I'm with Jonnybiker, get a second-hand 5/8" master cylinder, do an overhaul and save money, time, and trouble.

saltydog wrote:

Thanks for the heads up, but why would it lock up?
Robert

Mine had the smaller m/c with dual calipers. It locked up on me. Thankfully, I was just unloading it off a trailer and not on the road.

Too much pressure is exerted on the piston trying to pump enough fluid to a dual setup. It will probably be forever spongy feel, too, since it can't pump fluid fast enough.

Get a new/correct m/c!!

Well, I guess this will disappoint some of you, but the epoxy worked. I get a real sense of satisfaction in being able to fix things as opposed to replacing parts. To each his own.

What epoxy did you use?

Zthou1977 wrote:

saltydog wrote:

Thanks for the heads up, but why would it lock up?
Robert

Hi Robert,

They will lock up because of lack of "feel" in the brake lever. This site has a very handy chart to check for the best M/C-Caliper ratio: www.vintagebrake.com/mastercylinder.htm

Jeroen

PS: I'm with Jonnybiker, get a second-hand 5/8" master cylinder, do an overhaul and save money, time, and trouble.

ive never had issues with small mastercylinder locking up,more of a rider preferance in my experiance.