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.

 

No way, the maxim master cylinder should be cocked to bring it level, with the bars in straight ahead position. I would suggest yours is a Chinese replacement. Find an original and rebuilt that would be my suggestion.

 

Neither of my XJ700 or XJ700X have level MC's. They are stock.

 

I think the "Use Only DOT4" that wasn't introduced until 2006 confirms it is aftermarket

See below where OP identifies Nissin on his "original" master cylinder - lesson learned don't depend on Google AI :-(

 

not so sure about that, my xj600's, three of them, have stock master cylinders, stating the DOT 4 requirement, and mine are 1989 ,1990 (2of)

 

Yamaha changed the design on the covers somewhere along the way, and all current OEM Yamaha covers no longer have the raised YAMAHA wording as the original covers do. However, the original covers are interchangeable with the current covers.

Looking for the mfg.name NISSIN cast into the m/c body is the real tell-tale sign of an original Yamaha-supplied cylinder, just as Slackard mentioned. The original m/c for your bike has a 14mm piston bore, and use the "tilted" reservoir, again as Slackard mentions. A "level-orientation" m/c will sit tilted on any bike that had the buckhorn/"roto-tiller" handlebars (XJ650 Maxim, 1983 XJ750 Maxim, XJ1100, and some XS1100 models.....as some XS850 models too). The "tilted" reservoir m/c's,as used on buckhorn bars bikes (same that quickly 3 times.....) result in a m/c reservoir that sits "level" when installed on such "tilted" bars.

The should! Pictures?

 

Just got home from work, and I have a pic! Turns out it is an original after all.



Now, it still doesn’t sit perfectly level. On the center stand, bars straight, and it is slightly angled front to back. If I turn the bars all the way to the left, it is level front to back, but angled from side to side. Makes it annoying to really fill the reservoir properly, and the sight glass is basically pointless besides “is there fluid in there at all”.

 

Yea, iirc, if you loosen the m/c bolts on the xj (buckhorn bars), and turn bars to the left, like you said, you can level out the m/c pretty well(ish). Thanks for confirming its OE!