1980 KZ650 F1 Brake caliper rebuild, what size is it?

Hello, I'm new on here, I was on here about 15 years ago for a short while. I rode my bike from about 2001 to 2013 at which point I had an electrical problem and parked it. I recently had time to tackle that issue and now have more problems. My front brakes would not build any pressure, I took apart the master cylinder on the right handle bar and cleaned it all out as best I could, put in new fluid and bled it through the caliper until I had nice clear new fluid everywhere. I then had good pressure with the squeeze of the handle. I went for a ride and the caliper would not release at some point. I rode home with it stuck and hit some gravel, the tire locked up and I went down. Word to the wise, do not ride with a sticking caliper. So I learned my lesson there. After the smoke quit coming off the caliper I took it off and took it apart, it had kind of a yellowish color to it coating the inside, I'm not sure if that was from the old fluid or from the recently experienced extreme temperature. Anyway, I wiped it out, it looks pretty good, but I want to replace the rubber ring that goes around the piston. It just doesn't slide in and out easy like I think it should. I looked for a rebuild kit and am not sure if it is the correct one. I measured the diameter of the piston at just shy of 1.7". Maybe 1.684. I can't say for certain because I have forgotten how exactly to read my old calipers. Doing the math it is roughly 42.8 mm. So I looked on Z1 enterprises at part # KL32-1289 It lists a bunch of KZ bikes but not the F1, and it states it is for 42mm. Is this the right rebuild kit? Is 42 just a nominal measurement? Can anyone point me to just the one square O ring that goes around the piston, the rest of the rubber looks pretty good, good enough for stopping dust, not cracked or torn. I have a clymer repair manual that suggest taking it to a shop, it wasn't much help.

I searched the forum and read that there is a some kind of a pressure release or blead port in the master cylinder that can plug up. I don't understand what that is exactly. does anyone have a picture of that port in the master that plugs, maybe I missed it. I guess if someone can recommend a rebuild kit for the master too that would be good. Thanks for your help.

Frogwart wrote:
I searched the forum and read that there is a some kind of a pressure release or blead port in the master cylinder that can plug up. I don't understand what that is exactly. does anyone have a picture of that port in the master that plugs, maybe I missed it. I guess if someone can recommend a rebuild kit for the master too that would be good.

Caliper piston OD: 43 mm (exactly 42,85 - 42,90 mm) / Height: 41 mm

Scirocco, Thanks for the article. It is so much better than the repair manual I purchased. I see that port you have the red arrow pointing at and remember seeing the indentation but that it was not clear all the way through. Do you know what size the smaller portion of the hole is supposed to be? I imagine it is important if I try to clean it out that I do not enlarge it so the vacuum on the release stroke is maintained at factory specs. Also thank you for the OD of the caliper piston 42.85 to 42.90 mm, that means I was within a few thousands of an inch with my old fashioned plastic calipers.

Sorry, never do some measurements on the MC ports but the relief port is very tiny, less than a 0,50 mm in diameter. So be careful when cleaning your MC.
Do you have any inside view pics of the MC and his ports?

Partzilla is a good source for OEM parts. Once you find the part number then you can check ebay to see if there are any discount parts available. The OEM caliper seals are guaranteed to fit but aftermarket brands, like K&L, are not. Oh, and since your brake system was all filled with brown sludge that means the inside of the brake line is coated too. You best plan on replacing those too since they will contaminate your otherwise clean brake system.

Searching the Kawasaki part number: Z1Enterprises.com >>> 43020-1012 >>> PM81-3143 . Fits various models & the 650-F1.
I don't know what brand it is. The oem rubber parts may still be available from Kawasaki or Partzilla.

I installed a K&L caliper piston & rebuild kit from Z1Enterprises with no problems, but as indicated by Nessism, apparently sometimes
they may not fit. I've never had a problem with K&L, though, and everything I've replaced appeared identical to the old parts.
K&L parts are made in Japan.

I wasted several hours troubleshooting problems with TWO different brake systems that eventually were traced down to K&L caliper seals that were too tight and not allowing the piston to move close enough to the disc. Both of the bikes in question were GS Suzuki's though, not KZ's. For the nominal difference in price I don't think it's worth messing with aftermarket parts like caliper parts unless OEM is not available any longer.

Scirocco, I took the MC apart again and got a few pictures. I was able to clean the relief port with a torch tip cleaner at 0.020" which worked out very well. Shining a flashlight through the 1/2 bore of the MC after cleaning I was able to see light through the relief port. The 1/2 bore looks very good. I decided to put everything back together again after the cleaning and found the brake system to work just fine. Thank you for your help.

martin_csr, Thank you for pointing out the Piston on Z1Enterprises. This indicates to me that the sizes referenced in the part descriptions are nominal.

Nessism, Thank for pointing out that I should also change out the brake lines. This makes sense since the bike is so old and the lines are original. I'll be checking out Partzilla soon. Despite the brake system working after cleaning the port Scirocco helped me locate, I intend on getting proper replacement parts.

And do not use anything else than brake fluid or brake piston assembly paste to put the MC/caliper and piston/seals together! Anything else can destroy your new seals.

Hi,
Does any body know what is the part no. for this piston caliper ring?

Here are some pages from a F1 parts list
 

This metal ring holds OD of the dust seal in place and is press into caliper piston bore resess. I can´t find any part#!