Master Cylinder question

[sprinta]

Can anybody advise what the smaller hole diameter is inside the fluid chamber?

Just had the M/C re-anodized and there was a bit of crud from the process in the hole. Have passed a 0.5mm drill by hand through it but wondered if I need to pass a larger drill through it?

Thanks

Andy

[Green1]

Couldn't tell you. But I shouldn't think giving the drill bit a gentle wiggle would hurt.
How hard can the crud be?

[Mr_Sheene]

It's the Vent Port/By-Pass Port. The piston can't return correctly without it, so you do need it. It should not be enlarged. It's there to allow equilibrium.

Please have a look at have a look at
https://www.freeasestudyguides.com/brake-master-replenishing-port.html

This explains it better than I can.

Also, when you rebuild the M/C, make sure that the port is not blocked inside, by the positioning of the piston/seals.
I know this because I once thought that I was so clever that I could improve the brakes on my R90S. I was wrong - not for the first time!

[Green1]

Should have said gentle wiggle to remove crud not to enlarge the hole.
Not once have I ever thought about drilling it out.

[sprinta]

Thanks for the replies and advice. It was because of being conscious of not enlarging the hole that  I did not want to pass anything too large through it, hence try to establish it's normal dia.

Have used the 0.5mm drill, which I am sure is smaller and a syringe with some alcohol which will have hopefully cleaned the crud out.

Andy