Yep, what Alan said John, Honda cheaped out the forks and only chrome plated the tubes below the bottom triple, so the last 10 inches or so of bare metal rusts quite badly. The phosphoric acid cleans the rust off and leaves a protective layer so it won't rust there again. You've just reminded me that I left a rusty gas tank in my phosphoric bath, I must pull it out, no doubt it'll be rust free now, but the interior will be black too after sitting for so long, oops.
While we're on the ol' K2 Bitsa thread, I replaced one fork tube over the last few days, and it was an adventure. The left OEM tube was weeping, due to a previous owner (the numbnuts Ebay seller in the US) using a pipe wrench to twist the fork tubes out of the triple clamps. It wouldn't have been a problem if he'd scratched the sh1t out of the hard chrome 4 or 5 inches above the seals, but he didn't, and when I peeled back the gaiter and saw the carnage I tried to rub it out with wet and dry sandpaper and replace the seal, but to no avail, and on my 400 mile ride to Bairnsdale and back the bike went really well, but the ATF dribbled out and into my brake pads, and over my engine, which pissed me off.
K2 Bitsa forks 22 Jun 2021 2 by
Terry Prendergast, on Flickr
I bought two sets of fork tubes from Cruizinimage in Japan. I opened the box, they tubes looked good with just a cursory glance.
K2 Bitsa forks 22 Jun 2021 5 by
Terry Prendergast, on Flickr
so I pulled the left leg off the bike, separated the tube from the aluminium slider, transferred the spring and damper rod and slid it into the new fork tube, and ........ it fell out the bottom! WTF? Unlike my OEM fork tube, the Cruizinimage one didn't have anything in it to stop the spring and damper rod falling thru. Great..........
K2 Bitsa forks 22 Jun 2021 4 by
Terry Prendergast, on Flickr
I measured the overall length of the OEM leg, and noted that it's also 15mm longer than the Cruizinimage one. Inside the OEM leg there appears to be something pressed into the inside of the fork tube, so as it was buggared anyway, I sliced it open with my angle grinder for a look.
K2 Bitsa forks 22 Jun 2021 6 by
Terry Prendergast, on Flickr
So you've got a short "tube", with a castellated piece sitting in the upper most part which is a fairly close fit around the damper rod ("Damper Rod guide"?) and a thick washer/spacer above that, and the whole shebang looks like it's pressed into the machined out portion at the bottom of the OEM fork tube. Bugger. Well the next problem was that I couldn't just insert that piece in the bottom of the Cruizinimage fork tube, as their tube was only bored to 27mm as opposed to 30mm for the OEM forks, and even if I was able to install them, the tube was 15mm shorter than the OEM tube, so the damper rod would hang 15mm higher than the damper rod on the OEM tube. Bugger again.
Well, when life gives you lemons, make Ginger Beer. I machined up one insert that would (I think) do all the things that the other insert did, but the finish was horrible, even though I was using a new indexable cutting tool. I gave up for the night, and came back on Saturday. Good thing I did, I was able to rethink it, and came up with a better mousetrap. The first one is on the left, and the new improved model, which I machined with a blunt old insert in one of my old tools, is on the right.
K2 Bitsa Forks 26 Jun 2021 by
Terry Prendergast, on Flickr
Rather than packing it with the damper rod guide, and then a thick washer etc, I bored the insert from either end so that the "guide" was fixed inside the insert, at the same distance from the top as the OEM guide.
K2 Bitsa Forks 26 Jun 2021 1 by
Terry Prendergast, on Flickr
I then ground the chrome off the bottom of the fork tube, cut/ground a nice deep chamfer and did some ugly, but penetrating, welds.
K2 Bitsa Forks 26 Jun 2021 3 by
Terry Prendergast, on Flickr
I had to (luckily) grind my ugly welds down to below the OD of the 35mm fork tube, because the fork tube is a fairly close sliding fit, so I ground some off, did a test fit, ground some more, and so on and so forth until it was a nice easy sliding fit inside the alloy slider.
K2 Bitsa Forks 26 Jun 2021 4 by
Terry Prendergast, on Flickr
I shoved the fork tube up into the triples.
K2 Bitsa Forks 26 Jun 2021 5 by
Terry Prendergast, on Flickr
I got so excited I must have forgotten to take any more pics, but when I reinstalled the slider, I was happy that the fender bracket mounting holes lined up perfectly with the lugs in the slider. Bonus! I reinstalled the wheel, calipers (after I degreased the brake pads and rotor) refilled the fork oil, installed the air fork cap on that side, installed a new speedo cable, and called it good. Tomorrow is supposed to be a really nice sunny day, so I think I'll finish work early, and take it for a ride to Heathcote, for a pie.
If you never hear from me again, it'll be because my welds failed while I was doing a sweet power wheelie, probably while doing the ton, and my front wheel fell off. Pray for me........