[xpd153]

My NX650 front master cylinder is not good shape. But I found new VT750,Shadow 600,Steed compatible master cylinder is available at reasonable price. But I was not able to find most critical factor, cylinder bore size description in the website page. Therefore I asked it.

xpd153: What about cylinder bore size?
(unqualified sales agent) Violet: Hi, the mount diameter is 24mm.

  one day later

xpd153: I am not asking mount size.
Violet: If you mean this part(she attached a photo which points mirror mount hole), the bore is 19mm.

 Probably she is a kind person

 one day later

xpd153: You don't understand what you are selling. I am asking about cylinder bore size. If you don't understand what I said, pass my question to a motorcyclist

 same day
Violet:Hi It is 14mm. Regards

 I needed 11mm cylinder. Therefore no further development with Violet.

 In these days, selling a master cylinder without knowing cylinder bore size may be industry standard level at ebay. You have to be careful at ebay

[robvangulik]

Did you use google to look for 'nx650 front brake master cylinder '? There  are lots on the internet, not just ebay.
Part nr. 45501man911.
Is 11mm the standard size? The only Honda i am sure of to have 11mm  master cyl. is the cb1 from the end of the 80s the successor to my 400 sohc.

[xpd153]

Even I did not check price of genuine master cylinder because it must be more than $100.
Importing used NX650 master cylinder is out of the question because it is more than 20 years old and expensive freight cost.
 In Japan, new generic Nissin 11mm master cylinder is available at 9500yen(US$ 85.0).

 However, a VT750,Shadow 600 and Steed 400 compatible master cylinder that Violet is selling at ebay, is tempting because the price is only GBP 17.00(including international shipping). And it is new.

Yes, 11mm  is standard for NX650. And there are a lots of 11mm master cylinder models today.
Like CB250F,Foltza,CBR250R,Fusion, Suzuki Skywave 400.....

 Finally I got a used CB250F(MF43) master cylinder at 2600yen(US$ 24.0) including Japan domestic shipping.
Because I am not a billionaire My plan is, cleaning this master cylinder which is less than 5 years old.

[robvangulik]

You made a good deal then.
Is the original master cylinder worn or really defect?

[xpd153]

The original one was broken during extracting the caliper pistons. The fluid spilled from other side of master cylinder piston because one of caliper piston strongly resisted against its extraction. Therefore replacing inner master cylinder parts was inevitable.

 Initial my plan was, replacing master cylinder inner parts. However, I was not able to extract master cylinder piston. I was able to extract the circlip by cheap Chinese $2.50 circlip plier.
 Next inner part is a metal ring plate. But it is tightly sticked with the cylinder. I tried hydraulic pressure, air pressure and physical impact. None of them worked. Only remaining option for me, is destroying it by  electric dril.
 But it seems quite high risk operation. And still needs genuine master cylinder repair kit. Probably it will cost me more than $24.
 However, there are tons of used 11mm Nissin master cylinders in Japanese auction site if you know the compatibility and have some technical skill.  Most of them have reasonable price tag.

 So, I changed my plan again. Now,used CB250F master cylinder is sitting on my desk. It has quite clear
fluid level glass. Probably it is less than 4 years old and no needs for cleaning internal parts now.

[robvangulik]

Replacement with a 'new' second hand one is indeed the better and cheaper solution in this case, you can always try to repair the old one afterwards.
And you have some spare parts like the cover and screws to put away for when you might need them.

[xpd153]

Attached photos are about ex CB250F(MF43) master cylinder which has 11mm bore size.
 

[robvangulik]

It looks like new, and was the handle included? Always good to have one as a spare!

[xpd153]

The lever is included. The mirror is ported from NX650.
Only difference from NX650's master cylinder is, slightly smaller reservoir. But I think it will be
no problem.