is this brake piston usable?

I rebuilt my calipers and put this piston back in. can't imagine everyone elses' are perfect. just wanted feedback for myself and for everyone else to see. this was not an outdoor bike and does not have rusted parts. My brakes Did seize which caused the rebuild but I believe that was from air in the lines

 

On most Caliper Pistons there is a "Shadow" showing the portion of the Caliper Piston that is not protected from the elements -- always remaining outside the Caliper Seal.

Pitting and Tool marks on that area are not a serious problem.

Those marks on your Piston look to be with the "Critical Area" of where the Caliper Seal NEEDS to be in contact with UNBLEMISHED Piston Surface.

The Piston you have, there, looks to be pitted in the worst possible area.
It looks like that Piston is ruined.

You need a New Piston.
Or, a replacement Caliper and Piston.

 

I gotta agree with Rick on this one; if the pitting falls in the area where the new seals ride, it's not going to be reliable and is in fact, dangerous. You have some pretty severe deterioration there; it WON'T hold a seal. I'm not that familiar with the 650R's front brakes (yet) but that looks to me to be in the seal area.

I re-used this one, but as you can see the pitting was relatively minor and confined to an area outside that swept by the seals:

 

new pistons are on order, but I wanted to ride this weekend, but the bleeding process of a new system has been absolute torture.

so I took a giant syringe and hooked it up to the bleeder screws, one at a time.

Two things questions
- the bubbles Never stop coming (MC cover off, bleeder screw open), 4 reseviors worth! could it be pulling air past the rust spots on the pistions? (complete new brake system except pistons). prior to this I got to the point where the bleeders weren't putting out any more bubbles but my friend told me air is stuck in the MC area and to release the banjo's until I get a stream there while the lever is depressed, did that but lever was still soft, so i had the syringe idea
- I can pull bubbles up through the bleeder screws when they're locked! both of them. does that make sense?

one pad is still not touching one side of the disk on both sides (dual front disk). Thanks

 

-you can pull air PAST the threads of the bleed screws when they're locked, it's a "false positive." It also happens when they're unlocked, causing you to think you're still getting air from the caliper.

-a couple of quick wraps of teflon tape will minimize or cure that; but be careful not to block the hole.

-you've still got air trapped; yes you could be pulling air past the bad spots on the pistons if they are where the seals are trying to work; and the process is frustrating as all get out even after you've done it a half-dozen times.

-depending on how far apart the system was, cracking unions loose may or may not help; it just takes quite a bit of doing to get all the air out of the system.

My personal theory is that the machining marks on the inside of the caliper bore trap "microbubbles" that take a while to bake out of the fluid; "heat cycles" really seem to help the process once you get the brakes useable.

 

your kinda wasting your time bleeding the system untill it's back together anyways.

the best way i've found is to use a vacuum pump at the caliper. open the bleed screw and pull vacuum through the bleeder. sucks the fluid down through.

if there's a harborfreight in your area. they sell a brake bleeder pump kit for $25.

 

Fitz and Snowy, a combination of both your input lead to my success.

- I drained the system
- teflon coated the bleeders
- attached large syringe to one bleeder with other closed
- aspirated the fluid through the system, before the MC emptied I would empty the syringe into it
- about 3 cycles of the above procedure for each caliper and it was done, 15 minutes!!!

and if that wasn't good enough, not 1 single drop of brake fluid anywhere

no pumping during the procedure, they work Sweet

learning how to do this: 7 hours and spilled fluid on new caliper and MC paint job