Topic: worn, stuck fork piston on CB750K1 type fork; what now? (see pix)

[ksteve]

I'm rebuilding the front of my CB750K2, which has the earlier K1-style forks. The left-fork piston slipped off fine by hand. It showed only moderate wear:



But the right-fork piston looked like this:



It was seized on the tube, and showed heavy uneven wear on one side.
It was not persuadable by gentle means, so I heated it a little and used the gear puller to ease it off:



Piston looks fine on the inside:



I measured it and the other piston. Both are under the 1.551-inch limit listed in the Honda manual:



So what now?

-Does anyone make aftermarket pistons or have a stash of OEMs? (Honda doesn't sell them anymore.)

-Can I make my own, perhaps out of brass? (I have a lathe.)

-Do I just clean up these puppies and put them back in and live with slightly sub-par damping?

-Why would one seize? Is it a problem if it's a tight fit again when I reassemble?

Any advice and tales of your own experience appreciated!

Thanks,
Steve

[mrrch]

Polish it up and use, I don't think it will affect these simple forks too much.
Things seize after 30 years, may have had some water at one time (settles at the bottom)

[ksteve]

Polish it up and use, I don't think it will affect these simple forks too much.
Things seize after 30 years, may have had some water at one time (settles at the bottom)

Ah, yes: The first thing that came out of both drain plugs was copious amounts of water!
How does that get in there?

[coolgoose]

Hi ksteve

I remember struggling to find replacement fork pistons for my K2 last year when I was rebuilding my bike. I have two new reproduction fork pistons as spares with me. If you are still looking for replacing the ones on your fork and interested please PM me.

Thanks,
Sri

[Brantley]

Polish it up and use, I don't think it will affect these simple forks too much.
Things seize after 30 years, may have had some water at one time (settles at the bottom)

Ah, yes: The first thing that came out of both drain plugs was copious amounts of water!
How does that get in there?

If you still have stock gaitors and get stuck in a hard rain water collects beneath them and hangs out on top of yr fork seals until it evaporates... or seeps past worn seal. Take a look at yr gaitors- point those little drain/evap holes to the back. I've got in the habit of pushing them up off the fork sliders to soak up any water from a rain or wash and leaving them like that to dry 'til the next ride. I think Frank's Engineering might be able to help with the pistons- But I, too, would use the ones you got if they aren't binding anywhere.

[ksteve]

I have two new reproduction fork pistons as spares with me. If you are still looking for replacing the ones on your fork and interested please PM me.

Thanks, Sri. I PMed you.
Nice bike in your avatar!

[ksteve]

If you still have stock gaitors and get stuck in a hard rain water collects beneath them and hangs out on top of yr fork seals until it evaporates... or seeps past worn seal. Take a look at yr gaitors- point those little drain/evap holes to the back. I've got in the habit of pushing them up off the fork sliders to soak up any water from a rain or wash and leaving them like that to dry 'til the next ride.

That's it. Didn't think of those holes. And that's a great tip on pushing up the boots! Thanks.