Front master cylinder bore size?

[Cuppa500]

Hi folks,
I wonder if anyone can tell me the bore size of a stock xs1100 front brake master cylinder?

I've grafted an xs650 dual disc front end onto my Triumph 500 'special'. However the master cylinder, that I bought separately, (via ebay) is a single disc item, which doesn't give me enough pressure without pumping the lever. From what I've read elsewhere, the xs1100 m/cylinder is the way to go, but if I knew the bore size it might give me more options to choose from.

If anyone is interested I now have a single disc m/cylinder in excellent working order (I just fitted a new yamaha piston & seal kit) which I'd be happy to swap for suitable dual disc m/cylinder
regards
Ian

[John]

I just checked the front m/c on my bike and it looks like it has 11/16 cast into the bottom of the cylinder housing. It's kinda hard to read, but that would make sense as the rear is 1/2 in. Most any front master from a Japanese bike that has dual rotore and 7/8 inch handle bars should work. Just make sure the hose ends are the same type. The XS uses banjo fittings. Aguy here just installed the m/c from anFJ 1200 on his XS and it worked fine.

[TonimusMaximus]

Check out the thread that I made a while back. Describes what I did. Entitled "Front Master Cylinder" It's still on the front forum page.

[Ken Talbot]

JAT - but if you are able to get pressure by pumping the lever, your problem might be air in the system. These things can be very difficult to get all of the air out, even if you're using a vacuum pump. The other thing that will mess you up is old rubber lines that swell under pressure. Squeeze your left hand tightly around the hose, then pump the lever with your other hand. If you can feel the hose bulging, you've probably found a good part of the problem.

[Cuppa500]

Thanks guys, seems like it's 11/16ths I need, although it suprised me that a metric bike would have an imperial sized master cylinder.
The front brake system comprises of one single stainless braided hose, going to a 'splitter block' from which two rigid metal pipes go to the calipers. This is all new, the master cylinder has a new piston & seal kit fitted, & the calipers have new seals fitted. In order to be sure, I've tried every trick in the book to try & persuade more air out (& have been through several bottles of brake fluid in the process, scary in such close proximity to the bike's beautiful new paint job).
regards
Ian

[Jerry]

FWIW, the XJ uses a 14mm bore in the front MC. 'Course, it only moves one brake piston.....