81 XJ650 - Identifying a Master Cylinder

Rebuilt the master cylinder on my 81 XJ650 Maxim over the winter, and it’s occurred to me that it doesn’t look quite like any of the pictures of this bike online. Normally, I’ve seen master cylinders with the big “YAMAHA” branding on the cover, but mine shows no branding whatsoever. It also never sits completely flat on the buckhorn bars, even when the bike is on its center stand. This makes it a little annoying to bleed the brakes.



So, is this thing an aftermarket MC, or is it OEM?

 

Looks a lot like what was on my 82 xj650. I don't think mine had the big YAMA logo on it either. From the diagrams It looks like the correct/original MC & also looks like its in very good shape. Top of cap at angle (not parallel) to the piston bore, integral mirror mount, etc. Looks correct.

These integrated reservoir levers never sit completely level.. a modern caliper w remote reservoir is the only real solution.

Partzilla 81 XJ650 Master Cylinder

 

Huh. So, I guess there’s just different styles of stock master cylinder. I really wish they came up with some way for it to sit more level (would be easier to fill and bleed), but I suppose it can’t be helped.

 

I feel ya.. same story with my current xs85o "Special" project.. The MC what shipped with the 81 xs850 "special" has the off-angle reservoir (like yours).. They did that because the 80's stock buck-horn bars set the lever at a steep angle so they slanted the reservoir a bit to compensate (still, far from perfect tho). If you had the XJ "Seca", or in the case the of xs850 the "Standard" those bikes didnt ship with buck-horn bars and the MC reservoir cap was parallel to the piston bore (as pictured below).

It is what it is.. If you like you can run an aftermarket MC with reservoir angle (or remote reservoir) that works.. just make sure the piston bore is roughly equal to stock (likely 12 or 14mm diameter on your bike).

There is a good chance the MC is marked on the under side with the "NISSIN" logo along with the bore diameter. E.g, the image below is from some other bike, but you can clearly see where the NISSIN logo and bore size are shown..

The other tell-tale that yours is genuine original, is check see where the brake light switch fits into the MC.. Genuine yamaha would be just as pictured below.