[Track/S]

I must edit this, the pistons are aluminum, they have a nickel coating, I checked it with a drill bit.

[///MPhatic]

Bro, thank you for finally confirming! Now we just have to confirm if the 2NH/2NK is identical other than the color in this regard.

[Track/S]

Originally Posted by ///MPhatic

Bro, thank you for finally confirming! Now we just have to confirm if the 2NH/2NK is identical other than the color in this regard.

When I have a gray caliper removed I will remove a piston to confirm

[RobDucati]

Is there a piston rebuild kit? My pistons are corroded on the inside. I always try to clean them out well when I swap pads. I plan to rebuild the seals soon and thinking I might replace the pistons while I have it all apart.

Anyone have a part number(s) or a kit that can be ordered? I only see kits for the seals and boots from Girodisk.

[Track/S]

Originally Posted by RobDucati

Is there a piston rebuild kit? My pistons are corroded on the inside. I always try to clean them out well when I swap pads. I plan to rebuild the seals soon and thinking I might replace the pistons while I have it all apart.

Anyone have a part number(s) or a kit that can be ordered? I only see kits for the seals and boots from Girodisk.

Do you have any pictures of the corrosion?

[RobDucati]

Originally Posted by Track/S

Do you have any pictures of the corrosion?

No I don't. It was only in the center hole of the pitons and appeared to be aluminum corrosion based on the white color and soft dusty appearance. Reminded me of the crap on top of a lead battery or something you might see on an old boat. I used a small wire brush in an attempt to clean them up the last time I swapped pads. Looked like salt and water gets in there an is trapped causing the corrosion.

I found these https://racingbrake.com/bb-62bsp/ and thinking this may be a good option. Seems BMW doesn't offer the pistons separate from the whole caliper.

[Track/S]

Originally Posted by RobDucati

No I don't. It was only in the center hole of the pitons and appeared to be aluminum corrosion based on the white color and soft dusty appearance. Reminded me of the crap on top of a lead battery or something you might see on an old boat. I used a small wire brush in an attempt to clean them up the last time I swapped pads. Looked like salt and water gets in there an is trapped causing the corrosion.

I found these https://racingbrake.com/bb-62bsp/ and thinking this may be a good option. Seems BMW doesn't offer the pistons separate from the whole caliper.

Inox pistons on this link, you can buy them, they are better than the aluminum OEM ones, for my calipers I will make in titanium

[M3SQRD]

I was surprised to read they had Ti pistons. You can usually tell the difference when holding/touching Al and Ti - Alum has higher conductance so heat transfer is much higher than Ti which makes Alum feel colder to touch (higher heat transfer from hot hand to cold Al). Ti doesn’t feel cold to the touch because it has a considerably lower thermal conductance and, therefore, it’s more resistant to heat transfer.

[Track/S]

Originally Posted by M3SQRD

I was surprised to read they had Ti pistons. You can usually tell the difference when holding/touching Al and Ti - Alum has higher conductance so heat transfer is much higher than Ti which makes Alum feel colder to touch (higher heat transfer from hot hand to cold Al). Ti doesn’t feel cold to the touch because it has a considerably lower thermal conductance and, therefore, it’s more resistant to heat transfer.

I was confused by the nickel protective layer they have, it gives them a shiny appearance, it is difficult to differentiate to the touch, but I did notice that one of the pistons had a little corrosion, and that's when I knew that they couldn't be titanium since they titanium is very resistant to corrosion

[M3SQRD]

Originally Posted by Track/S

I was confused by the nickel protective layer they have, it gives them a shiny appearance, it is difficult to differentiate to the touch, but I did notice that one of the pistons had a little corrosion, and that's when I knew that they couldn't be titanium since they titanium is very resistant to corrosion

I agree with you on that one. When you created your original post I was surprised to read and see what appeared to be a piston that could have been Ti. Also, the nickel coating could throw off the heat conductance a little too. I just couldn’t believe a company that uses Al pistons in the Blue calipers would spend the money on Ti pistons for CCB or 2NH calipers. If they had used steel pistons on the Blue calipers then maybe I could see them using Ti pistons in the CCB and 2NH calipers. Basically, BMW is too cheap to mass produce Ti caliper pistons of five different sizes. CCB and 2NH rear calipers would be identical too if Ti was used. The cost associated with the machining/manufacturing of Ti is so much higher than Al, it can be cost prohibitive on space applications. We had no choice but to use Ti fittings when we had switched to a composite truss structure to reduce the inertia of the rotating side of a payload which forced us to use Ti plug fittings to match the EA (or Et) of the composite tube with a realistic thickness of an Al part because it allowed us to remove a lot more material between each plug tube due to its > 2-3 factor of yld and ult strengths of 7075-T7351 and 7050-T7451 Al alloys. Ti plug fittings were considerably lighter than the Al fittings of a similar design which further reduced the inertia of the rotating side of a payload.

[Track/S]

Originally Posted by M3SQRD

I agree with you on that one. When you created your original post I was surprised to read and see what appeared to be a piston that could have been Ti. Also, the nickel coating could throw off the heat conductance a little too. I just couldn’t believe a company that uses Al pistons in the Blue calipers would spend the money on Ti pistons for CCB or 2NH calipers. If they had used steel pistons on the Blue calipers then maybe I could see them using Ti pistons in the CCB and 2NH calipers. Basically, BMW is too cheap to mass produce Ti caliper pistons of five different sizes. CCB and 2NH rear calipers would be identical too if Ti was used. The cost associated with the machining/manufacturing of Ti is so much higher than Al, it can be cost prohibitive on space applications. We had no choice but to use Ti fittings when we had switched to a composite truss structure to reduce the inertia of the rotating side of a payload which forced us to use Ti plug fittings to match the EA (or Et) of the composite tube with a realistic thickness of an Al part because it allowed us to remove a lot more material between each plug tube due to its > 2-3 factor of yld and ult strengths of 7075-T7351 and 7050-T7451 Al alloys. Ti plug fittings were considerably lighter than the Al fittings of a similar design which further reduced the inertia of the rotating side of a payload.

Anyway, I have already ordered a titanium bar to make the pistons

[M3SQRD]

Originally Posted by Track/S

Anyway, I have already ordered a titanium bar to make the pistons

I’m not surprised 👍

[///MPhatic]

Originally Posted by Track/S

Anyway, I have already ordered a titanium bar to make the pistons

So all 2NH/2NK pistons are identical aluminum with a nickel coating?

[Track/S]

Originally Posted by ///MPhatic

So all 2NH/2NK pistons are identical aluminum with a nickel coating?

Yes, Bmw didn't make any changes....

[samsamdar]

Okay wait so just to confirm: all of the gold, anthracite, and red 2NH/2NK calipers are identical except for the color? And they all use alumnium pistons instead of titanium?

[Track/S]

Originally Posted by samsamdar

Okay wait so just to confirm: all of the gold, anthracite, and red 2NH/2NK calipers are identical except for the color? And they all use alumnium pistons instead of titanium?

Exactly.