repairing rusty fork tubes

[itayky]

Hi all,
In the attached pictures there's my front fork which I've just changed the seals on - very much thanks to the info in this forum, thanks guys!

For a long time I've been wanting to remove the rust stains I had on the fork tubes, but when I use a very fine sandpaper with some wd40 on those rust chunks, the rust comes off and on some occasions the chrome finish of the forks comes off with it and the bare metal is showing.
I suspect that if I don't use anything to cover the missing chrome it's quickly going be rusty again.
What can I use to paint over those little holes in the chrome and possibly give it a chrome-like finish and rust protection?

Thanks y'all

[mr72]

If it's pitted, there's nothing you can do short of replacing the fork tubes.

If you are really serious about reconditioning them in terms of making them seal better, you can fill in the rust pits with epoxy of any kind and then sand it smooth and polish it. But there's no way anyone is that serious about fixing these fork tubes.

It may leak a tiny bit due to the pitting. You can make the rust basically stop spreading and stop rusting by coating it with Breakfree CLP, and periodically spray some more CLP on it. It will dramatically slow the rust. The rust spots don't likely affect performance enough to worry about it.

[Joolstacho]

Your problem is that the rust pits will tend to wear your new seals more quickly as they rub up and down.
Obviously the best answer is new fork tubes, or have your tubes hardchromed and ground to size, but both these options will cost an arm and a leg!

In the past I've repaired this using thin cyano glue. (It's better than Epoxy because it's thin like water it actually wicks deeper into the metal). Carefully scratch out any loose rust using a scalpel, then using a THIN cyano glue such as 'Hot Stuff' put tiny drips into the pit patches, and the cyano should 'wick' into the corrosion. I often start by using a cotton bud to dab the cyano on. You might have to build up thickness by repeating. Then very carefully, using 1200 grade wet & dry on a flat sanding stick, dress the cyano back level with the chrome.

This technique also works well for pitted disc-brake pistons.

[RichDesmond]

You need new tubes. There isn't any fix (short of re-chroming) that's going to last.

[mr72]

In the past I've repaired this using thin cyano glue.

Yes this technique is commonly used on painted surfaces called a "drop fill". Around here "cyano glue" is aka "super glue". Loctite makes the best but anything will do. It's not nearly as durable as epoxy but it does fill easier.

If you really want to do it right then use a sanding drum the size of the fork tube in a drill press to create a radiused face on a wood block for sanding, that way when you sand it it will remain round. The classic technique of leveling a drop fill is with a new straight razor blade. Once it's fully dry, scrape/burnish or if you are really good, cut it like a plane would cut, with the blade parallel to the long axis of the fork tube (you want it to match the radius of the fork...). Careful not to scratch the tube.

Or, replace the fork tube. Seriously. This drop fill/polish thing is very time consuming and error prone, biggest part of the job is removing the fork tubes and tearing them down so why not just get another set on ebay? Way better in the long run.

[The Buddha]

You need new tubes. There isn't any fix (short of re-chroming) that's going to last.

That isn't a solution either. They use hard chrome - hexavalent chromium - on all hydraulic units which is essentially never available outside on the street AFAIK.
Worse yet, the underlying rust pit can not be covered up by a few thou of Cr 6 either.
Cool.
Buddha.

[Joolstacho]

"It's not nearly as durable as epoxy"

-That's just not right. You're using the wrong Cyano if that is the case.
The whole point about the thin 'wicking' cyano is that because it's so thin it soaks right into the metal 'texture' giving far superior adhesion to the substrate.
It cures very very hard, harder than any epoxy glue.
We use it in certain aircraft structural applications where these properties are required.

[mr72]

"It's not nearly as durable as epoxy"

-That's just not right. You're using the wrong Cyano if that is the case.
The whole point about the thin 'wicking' cyano is that because it's so thin it soaks right into the metal 'texture' giving far superior adhesion to the substrate.
It cures very very hard, harder than any epoxy glue.
We use it in certain aircraft structural applications where these properties are required.

As a gap filler (that is, filling in the voids left by pitting), I think epoxy will be a much better choice. And in my experience super glue is far more brittle and chips easily when used as a filler compared with epoxy. But there are a number of different epoxies. You could even use something like JB Weld for the fork rust and it would work fine but it still way too much work and replacing the fork tubes is much easier.

I won't argue about hardness or adhesion. Epoxy can be a real pain with adhesion and getting the surface just right, and some epoxies are just not very hard. But there's a big difference between durable (as a filler) and hard. The heat and flexing a motorcycle fork is subjected to, I think, is likely to cause cyanoacrylate glue to chip because it's not as flexible as the fork and doesn't tolerate expanding/contracting with heating. But it's all academic.

I have used CA glue many times for paint finish repairs (guitars mostly) and it works fantastic for that, that is a filler usage that gets virtually zero stress ever and doesn't have to tolerate any flexing or a lot of heat expansion. Still, for that purpose, I really prefer to use clear nail polish (lacquer) since it's much easier to work with and it's much more flexible and more importantly flexes the same as the rest of the finish in most cases so the bond at the edges of the chip or dent that I am filling will not separate. If it's a guitar with a catalyzed polyester or urethane enamel finish I'll use CA, if it's a lacquer I'll use nail polish. On a car finish I always use nail polish due to metal expansion and the need for flexibility. I know this is meaningless information for a fork tube repair but maybe someone wants to fix chips in their tank

[J_Walker]

my two cent. CA is optically clear, Epoxy will never be, there for - cosmetic things i go towards CA, for chemical resistance or flex related applications, Epoxy.

as far as the fork tube goes, replace it. if you live around the north east, you're gonna have a lot of marine machinist. they should be able to help out if you call around. A tube of chrome moly, true'd up on a lathe in theory should be a fine replacement. on the high end, non-best friend discount, its about $70/hr and should run about 3 hours for making up both. [a lazy machinist will say a total of 4] plus the cost of material, and maybe tooling [I have a guy who never charge for tooling, because he factors it in.] so if you can't find a good set for under 500 bucks total.. i'd start calling machinist.

Problem with forks, its one of those things that ALWAYs go on crashed bikes. so makes them hard to find. of course you will always find them AFTER you bought a pair.

[RichDesmond]

my two cent. CA is optically clear, Epoxy will never be, there for - cosmetic things i go towards CA, for chemical resistance or flex related applications, Epoxy.

as far as the fork tube goes, replace it. if you live around the north east, you're gonna have a lot of marine machinist. they should be able to help out if you call around. A tube of chrome moly, true'd up on a lathe in theory should be a fine replacement. on the high end, non-best friend discount, its about $70/hr and should run about 3 hours for making up both. [a lazy machinist will say a total of 4] plus the cost of material, and maybe tooling [I have a guy who never charge for tooling, because he factors it in.] so if you can't find a good set for under 500 bucks total.. i'd start calling machinist.

Problem with forks, its one of those things that ALWAYs go on crashed bikes. so makes them hard to find. of course you will always find them AFTER you bought a pair.

A fork tube is much more than just a steel tube, not something that can fabbed in a machine shop, at least not cost effectively.

[Bluesmudge]

Considering how cheap and plentiful GS500 forks are I don't see why you would bother repairing or machining.

Gs500 forks can be had any day of the year for under $200 on eBay and sometimes on craigslist. There are multiple sets on eBay now for under $100.  If you have a GS500E, purchasing a set of GS500F forks ('04+) gets you a set with slightly stiffer fork springs. Any used set of forks, plan on replacing the dust and oil seals.

[Joolstacho]

"I have used CA glue many times for paint finish repairs (guitars mostly)"

Coincidentally, me too mr...
www.whittakerdesign.com.au/guitars

[J_Walker]

my two cent. CA is optically clear, Epoxy will never be, there for - cosmetic things i go towards CA, for chemical resistance or flex related applications, Epoxy.

as far as the fork tube goes, replace it. if you live around the north east, you're gonna have a lot of marine machinist. they should be able to help out if you call around. A tube of chrome moly, true'd up on a lathe in theory should be a fine replacement. on the high end, non-best friend discount, its about $70/hr and should run about 3 hours for making up both. [a lazy machinist will say a total of 4] plus the cost of material, and maybe tooling [I have a guy who never charge for tooling, because he factors it in.] so if you can't find a good set for under 500 bucks total.. i'd start calling machinist.

Problem with forks, its one of those things that ALWAYs go on crashed bikes. so makes them hard to find. of course you will always find them AFTER you bought a pair.

A fork tube is much more than just a steel tube, not something that can fabbed in a machine shop, at least not cost effectively.

Actually, it really just is a steel tube... and I've had thicker walled ones made up for old 90s two stroke dirtbikes.
Also note I said marine machine shops. these guys are use to truing up and turning long, boat output shafts to the thou. asking one of these guys to turn up a set of forks is like asking a gunsmith to turn you up a steel skewer. lol

A set of fork tubes for my dirtbike ran me 200 dollars, and that's from already having bought the material stock to use as said fork tubes. and my machinist was confident enough that it would work just fine and would be stronger then the stock ones for sure. [bent 2 stock ones hitting turtle holes] but I get the good buddy discount with my machinist. not the just met you, bend over discount.

[RichDesmond]

my two cent. CA is optically clear, Epoxy will never be, there for - cosmetic things i go towards CA, for chemical resistance or flex related applications, Epoxy.

as far as the fork tube goes, replace it. if you live around the north east, you're gonna have a lot of marine machinist. they should be able to help out if you call around. A tube of chrome moly, true'd up on a lathe in theory should be a fine replacement. on the high end, non-best friend discount, its about $70/hr and should run about 3 hours for making up both. [a lazy machinist will say a total of 4] plus the cost of material, and maybe tooling [I have a guy who never charge for tooling, because he factors it in.] so if you can't find a good set for under 500 bucks total.. i'd start calling machinist.

Problem with forks, its one of those things that ALWAYs go on crashed bikes. so makes them hard to find. of course you will always find them AFTER you bought a pair.

A fork tube is much more than just a steel tube, not something that can fabbed in a machine shop, at least not cost effectively.

Actually, it really just is a steel tube... and I've had thicker walled ones made up for old 90s two stroke dirtbikes.
Also note I said marine machine shops. these guys are use to truing up and turning long, boat output shafts to the thou. asking one of these guys to turn up a set of forks is like asking a gunsmith to turn you up a steel skewer. lol

A set of fork tubes for my dirtbike ran me 200 dollars, and that's from already having bought the material stock to use as said fork tubes. and my machinist was confident enough that it would work just fine and would be stronger then the stock ones for sure. [bent 2 stock ones hitting turtle holes] but I get the good buddy discount with my machinist. not the just met you, bend over discount.

What about the check valve inside the tube that allows the separation of compression and rebound damping??

[J_Walker]

check valve was re-used on mine. he did something I forget what, think he had to make a bushing or something in order for the OEM one work with the new ID of the new tubing. everything was reused expect the outer tube itself, and the springs + spacers.

I'm not saying its cheaper, but there may come a day very soon, that GS parts are hard to come by. and this is always an option.

[RichDesmond]

check valve was re-used on mine. he did something I forget what, think he had to make a bushing or something in order for the OEM one work with the new ID of the new tubing. everything was reused expect the outer tube itself, and the springs + spacers.

I'm not saying its cheaper, but there may come a day very soon, that GS parts are hard to come by. and this is always an option.

Interesting. That valve isn't a removable part on a lot of tubes, not sure if it is on the GS.

[The Buddha]

check valve was re-used on mine. he did something I forget what, think he had to make a bushing or something in order for the OEM one work with the new ID of the new tubing. everything was reused expect the outer tube itself, and the springs + spacers.

I'm not saying its cheaper, but there may come a day very soon, that GS parts are hard to come by. and this is always an option.

Interesting. That valve isn't a removable part on a lot of tubes, not sure if it is on the GS.

I'm not sure what valve you're talking about but there is a sort of precision machined metal ring that can move a bit side ways but seals up against the damping rod that's sort of captive in the fork tube about 2-3" off the bottom, that may have to be somehow removed and transferred onto the new one.
However if it was installed in the old one, dont know how it wont be installable in the new one, obviously a human or a machine did it after the forks were finished and chromed etc etc.
Cool.
Buddha.

[RichDesmond]

check valve was re-used on mine. he did something I forget what, think he had to make a bushing or something in order for the OEM one work with the new ID of the new tubing. everything was reused expect the outer tube itself, and the springs + spacers.

I'm not saying its cheaper, but there may come a day very soon, that GS parts are hard to come by. and this is always an option.

Interesting. That valve isn't a removable part on a lot of tubes, not sure if it is on the GS.

I'm not sure what valve you're talking about but there is a sort of precision machined metal ring that can move a bit side ways but seals up against the damping rod that's sort of captive in the fork tube about 2-3" off the bottom, that may have to be somehow removed and transferred onto the new one.
However if it was installed in the old one, dont know how it wont be installable in the new one, obviously a human or a machine did it after the forks were finished and chromed etc etc.
Cool.
Buddha.

Yep, that the check valve. There's a good explanation of how it all works on the Race-Tech site:

http://racetech.com/html_files/dampingrodforks.html

[The Buddha]

Ah, cool.
Anyway, I have an easy solution for the OP.
You want to repair them by setting them to katana forks.
I find those actually hold up a lot better too. Or GSXR USD's
Cool.
Buddha.

[GS Man]

My opinion
Dont repair, too much faffing around, by the time you have them all stripped down you may as well replace. Do some research
and shop around. There are decent used forks on eBay or new tubes can be bought for a reasonable price if you shop around.
Im re building four pairs of forks at the moment. All of them looked like your picture, I tried the superglue repair but wasn't happy with the look or the feel I could still feel slight imperfections around the repairs plus if any of these forks were left outside in a wet environment then it wouldn't take long for new corrosion to come through. I decided to replace all with new. You will have to remove the valves from the bottom of the tubes and install into the new tubes. I had a suspension guy do that bit for me quite cheap, don't know how he did it but it didn't take long.
If your forks are an early 1989-1991 then I recommend installing the longer springs from 2000 and cut down the spacers accordingly.