This follows on from my post on planning a brake upgrade for the Honda XR250 BAJA (the Japan-market XR250 / MD30):
To improve the XR BAJA's brake feel and control, I decided to replace the brake caliper pistons.
From what I found, Kashima-coated pistons the same size as the XR's are available from both Honda and Yamaha.
Honda sells the pistons on their own, while Yamaha's come as a set with seals, so I got the Yamaha ones.
The brake caliper itself is made by Nissin, so either Honda or Yamaha should be fine.
These are the pistons I got. The photo is after opening it, but the bag contained two Kashima-coated pistons and two sets of dust seals and piston seals.
I compared the sizes. It looks like they'll swap over.
The Kashima-coated piston felt very light, so I weighed them.
I never expected it to be this light.
Switching to Kashima-coated pistons looks like it brings weight savings as well as better brake feel.
Now for the replacement.
When overhauling a brake caliper, coating the seals and pistons with brake fluid or silicone grease makes assembly smoother.
Here I used Metal Rubber, which is compatible with brake fluid.
Brake fluid itself would probably be best, but it seems to be very aggressive towards paint, and I didn't want to spill or splash it, so I didn't use it at this stage.
I'd also read that silicone grease doesn't dissolve in brake fluid, so I didn't use that at this stage either.
All that's left is refitting the brake caliper and brake hose and bleeding the brakes.
Here I'd also stripped the brake caliper and removed the brake hose, but you can replace just the pistons without going that far.
When you replace the pistons, you must change the brake fluid and bleed the air out.
I plan to write up my impressions after the piston swap in a separate post.