Help needed - Master-cylinder rubber seal

J3 has the same piston assy as the J1/J2 & a bunch of other dual disk models, so it's probably 16mm.

I don’t know what’s J’s OEM diameter. I’ll try to find the info or measure one I have here.

I have here a quite old master-cylinder that I believe is coming from a 1983 KZ750L which incidentally, have the same exact p/n than a 1983 1000 J3. J1/J2 have another p/n.
I just took apart and measured the piston and bore and it is less than 16mm. So, more than likely, it is a 15.87 mm.
Then, if I take the same road than ZRX guys, a 14 mm diam. master-cyl. will work.
Many thanks for all your comments!

I think the main difference between the J1/J2 and the J3 is the brake light switch. The J3 uses the more modern switch that attaches to the bottom of the master cylinder and is activated by the brake lever.

wrote:

I think the main difference between the J1/J2 and the J3 is the brake light switch. The J3 uses the more modern switch that attaches to the bottom of the master cylinder and is activated by the brake lever.

What about J1/J2 switch? Is it a fluid pressure switch?

no. it has the same type of electro-mechanical switch as most other KZs and operates electrically pretty much the same as the modern style J3 switch.  you should be able to hook it up exactly the same.

HELLO I READING YOUR POST FOR A PART TO MASTER CYLINDER 
THE RUBBER YOU NEED IS JUST FOR DUST  AND IT SERVE FOR NO PRESSION ON MASTER

dust seal helps to keep the piston & brake fluid clean.

TexasKZ, fyi, I ordered a dust seal for an EX500 and it fits right in. My MC is not an EX500 OEM but the seal fits anyway. Thanks for the hint!!!

Hurray for simple solutions!