Brake master sight glass size?

[GleepGlop]

I'm measuring 16.5mm inner diameter with digital calipers, that is the first part from the outside before you get to where the o ring goes.
I could easily be wrong about what size to order, does anyone know for sure?

[scrambler]

I'm measuring 16.5mm inner diameter with digital calipers, that is the first part from the outside before you get to where the o ring goes.
I could easily be wrong about what size to order, does anyone know for sure?

The outer diameter of an original Honda sight glass (OEM 45515-MA6-006 https://www.webike.de/products/24975778.html) is 18 mm. The sealing O-ring is OEM part number 45516-MA6-006 https://www.webike.de/products/24975779.html. Unfortunately, the small aluminum reflector is sold out, so you have to carefully remove the old one and reuse it.

NX250 sight glass brake master cylinder.jpg

Two of the cheap Chinese-made glasses became brittle and broke after just a few years viewtopic.php?t=735.

Therefore, every NX250/NX650 rider should stock up on one or two of these Honda sight glasses while they are still available

[GleepGlop]

I did buy cheap sight glass 2 pack on Amazon 18mm and it seemed like the glass part was going to be too wide to press in, but as long as I don't damage the housing I can try it. I read through your thread you linked, it seems they don't like brake cleaner, but do they react to the correct brake fluid? This one I think is glass whereas the Honda one is plastic I noticed.

[scrambler]

I did buy cheap sight glass 2 pack on Amazon 18mm and it seemed like the glass part was going to be too wide to press in, but as long as I don't damage the housing I can try it. I read through your thread you linked, it seems they don't like brake cleaner, but do they react to the correct brake fluid? This one I think is glass whereas the Honda one is plastic I noticed.

Are the Amazon sight glasses made of real glass? Please provide a link—I’ve never seen those before. The idea that the Chinese-made glasses couldn't handle brake cleaner was just a guess after the first failure. However, a second glass also became brittle after a few years. I can't say for sure if that's due to the brake fluid, but the lifespan is definitely limited. Once they start to cloud over, cracks soon follow. But as long as genuine Honda sight glasses are still available, there’s no problem either.

[GleepGlop]

This is what I got https://a.co/d/0frYOhXz

I just tried pressing it in with a small 4" vise with soft jaws even though it looked like it was going to be too big, and I may have damaged the housing because the o ring went in easily at first and now I can't get it back in because I've pushed the housing in slightly I think. I've attached pictures. It's a 1988 Canadian NX 250, the cylinder is a Nissin 3B52. It seems to want at 16mm sight glass. I gently used the vise with soft jaws until I felt resistance and backed off to see if it started to go in. I can't remember if the housing was flush or was it slightly recessed, but suddenly the o ring won't go back in where it went in easily before.

[GleepGlop]

Another possibility is that the ring from the old sight glass is still in there (2nd photo?). The old one came out in several pieces which I threw out, so I'm not sure if the old ring came out now. That would explain why it seemed like things got tighter because I pressed the ring in further.

[GleepGlop]

Live and learn, the old ring was still in there and that explains everything lol! Should be no problem to press in new 18mm sight glass now.