Fork Leg Remedial Fix

[groily]

That is one of those 'three hundred million light years from earth' sequences from that new far-away telescope, surely? (Or some very horrible self-administered medical procedure!)
As you say, not sure what it really says, except there is a "bit o' this and a bit o' that". Doesn't help with measurements for round, parallel, straight on the portion of the slider that the bottom bush travels over.
I guess it's worth trying with your honing flappy thing, to see whether a bottom bush can be encouraged to pass smoothly, but a worn slider should not need an UNDERsize bush, should it?
I fear you might be farting against thunder here but as a 'glass is always half full' person, I have my fingers crossed for you.

Have you thought of making one or more dummy bottom bushes which you might be able to pass down the leg - with the upper bush in place to hold the stanchion straight - and then with the merest hint of grinding paste on the dummy rotate the leg while pushing/pulling? Possibly with the tiniest amount of taper put on the lower part? Working up a gnat's cock's worth at a time using successive dummies until you get to 'correct' size. And then seeing, with the correct dimensions, how much slop and wear there is across the range of movement of the fork?
A bit of work, which might only prove it is scrap for being oval, bent, too far gone, and wiser heads may say that's a bad plan . . . . but as you're on a hiding to nothing here, I think if it were mine I'd try something along those lines just so I could say 'I tried'. (While keeping an eye out for a replacement.)

[RichardL]

Groily,

Thanks for jumping in here. I do feel a bit guilty for dragging you, and anyone, into watching the dizzying endoscope video. It wasn't what I expected, but it wasn't a big investment, either.

At the risk of sounding disingenuous, yes, I did think about a grinding paste approach, but your description gives clarity for how to go about it. In my blurred vision of it there was a stepped gauge with bluing to tell me where to start. Oh boy, more work using the lathe for the reason it was bought.

As for bent or crushed, I'm having trouble reckoning how that might have happened since the restoration in the early aughts. Though, I was surprised to find that the tube material has such a thin wall, I think, around 0.075". Edit: Bear in mind, my ignorance when the forks were first put together was, somehow, and impossibly, more profiund than it is now.

Again, thanks.

Richard L.

[Greybeard]

Oh RichardL, what a mucking fuddle! 😞

[RichardL]

About to start the clean up of the leg and just showing the flapper tool made from a stanchion and loaded with 150 emory cloth. Note the separation of the cloth to get around the bottim pin and the drill drive using the puller device. Also, I'll pour a bunch of oil in the leg.
Edit: Also, added the gold nail polish to alert me whe near the top
Richard L.

[RichardL]

Why not dry?  Is that just going to create a huge mess and polish instead of hone?

I wouldn't use oil.  I do not understand what the advantage would be.

I don't take wet sanding as polishing as much as a way to keep the paper from loading up. In any case, I wanted to start with very light removal of material, really, just the surface rust, then, I'm going with grinding paste on one or more scrificial bushings. If that doesn't get it, I'll probablt move to the brake cylinder hone.

BTW, like minds, and all that, I did consider separating the pieces from one of my spare (thought to be useless) fork legs to explore the possibility of real restoration.

Richard L.

[RichardL]

Fine, yeah the tube replacement would be interesting, it would be good to hear from an engineer how easy it would be and what it would cost.

I seem to remember the threaded collar and fender bracket being brazed on so the real issue would be the weld around the base.  I think a good welder could do it fairly easily without creating distortion.

I've been using a class-A (my term) certified welder for my serious welding needs (for which I am definitely not good enough), who would have no trouble with it at all. Probably $75 (his minimum) to $100 for the whole thing if I build the fixture.

Richard L.

[RichardL]

Your first reaction should be, "Jeez! you haven't fixed that yet?" I think I l lost track of the fact that this problem started two months ago and, basically, ruined my summer of riding. My job has been very busy (is my excuse). Anyway, on with it.

Does anyone know, or have a brand-new one to measure, the OD of the lower fork bearing (29-5347). I have brand new uppers to measure, but have cocked up my new lowers such that any measurement is suspect. Feked posted the dimensions, but they are also suspect.

Thanks, in advance.

Richard L

[muskrat]

G'day Richard.
My new spare measures 37.45mm = 1.474"
Cheers

[RichardL]

Thanks, Musky, that really makes sense, since I stupidly sanded off several thou from mine. I'd be interested to hear if anyone got someting different, just to know what the consistency is.

Anyway, after trying to drive in a sizing mandrel with the lathe, and a lot of honing with the lathe, I could not get a 1.472" bottom bearing to make it to the bottom. Decided there must be a dent I can't see. Removed all the paint and, sure enough, about 2-1/2 to 3" of the bottom of the tube is depressed in. My next attempt is to heat the tube to a light glow while diving in the sizing mandrel. I just need to know the correct size mandrel since I now have two that are too small. You could say I'm trying to maximize the fun/value of the lathe.

I don't remember any such trouble when I first put the forks together in 2006, but I was even dumber then.

Richard L.

[RichardL]

Musky (or anyone caring to chime in),

I should have asked, what clearance is about right for the fork bottom bearing? (It sounds weird to call it a "bearing", but that's what the parts book says.)

Richard L.

[RDfella]

A thousandths of an inch would be fine. When you get your mandrel into place under the tight spot, gently hammer on the fork leg against the mandrel to help it into shape (flat hammer, not ball).

[RichardL]

RD,

Thanks. I hadn't thought of it as body work like that. Are you saying do try that cold? As I mentioned, I was planning on getting the tube to a just-plastic state with heat, then, shoving in the mandrel. I'm guessing that process won't be controllable to 0.001" tolerance. If lucky, maybe I get 0.002" uniform. If unlucky, I might end up doing what, perhaps, I should have done in the first place, shop for the best replacement I could find. Problem is, the seller isn't going to show any photos down the tube, so it's still a crap shoot.

Some photos attached: 1. trying to show the indentation; 2. showing the mandrel; 3. showing the setup in the vice.

Richard L.

[RDfella]

Hi Richard,

Get the area with the dent to a dull red and drive the mandrel in. Then a gentle tapping in that area (as you say, bit of panel beating to get the damaged area to conform to the mandrel). Preferably after it's cooled a little (and shrunk onto the mandrel!). Doing that when red hot creates a risk of stretching the metal and consequential 'pr*ck in a shirtsleeve' fit. You say the dent is near the bottom? Not an area the bottom bush visits much - especially with the brakes BSA fitted - so the fit should end up pretty good.

[Joolstacho]

One of the difficulties is that the fork sliders 'bell out' and wear where the lower bush slides, so a standard bush might fit lower down but have too much slop when in the 'active' area.
I have 2 sets of BSA sliders which have this problem. I recently did my Velocette sliders. These have the upper and lower lugs soft-soldered (yes, soft soldered) to the actual tube. So you can replace the worn section, mind you, it's tricky soldering and no easy thing to do!

[RichardL]

J,

How did you acquire the exact tube (or tubing)?

Richard L.