Topic: bent fork issues

[the technological J]

so lets say some one laid down their bike the other day (hypithetical) and bent the forks.... outside of buying new ones  and paying some else to fix them how could one repair this bend themselves?

[campbmic]

Try substituting the forks for pipe cleaner. Back when I was your age we didn't even have forks, we used string to hold our front tires on... and that was if you were lucky enough to be able to afford string.

 

To be honest, I don't really now if there is a good fix for bent forks. When I'm on the highway and I look down to my forks vibrating and moving back and forth its pretty scary. I've always had a fear of my front tire popping off, or my forks snapping and just doing an 80 mph face plant. I think you might save yourself a lot of worrying if you just buy new ones, most likely reuse springs and some internals if you don't go abouts upgrading.

These are just my opinions though, and for the most part my opinions are usually proven wrong.

[mick7504]

We used to straighten a lot of fork tubes back in the 70's providing that they weren't too badly bent.
A lot of bikes that just needed new oil seals had a bit of a kick in the tubes.
They weren't bad but they were also not dead true.
We had a milled plate that the fork tube was rolled on to find the high spot and then set up in "V" blocks in a workshop press with a magnetic based dial indicator and we'd straighten them to less than .001" of runout.
It was a bit time consuming at first but after a few you got the idea.
Mick

[campbmic]

This is kind of off topic. On back of the fork ears on my bike (The area on the fork ears that is directly facing my tank) there are two fairly big sized dents. I've looked at a couple other CBs and they all have these same dents. Can anyone explain? Are the supposed to be there or is it from like a low fork oil issue?

[faux fiddy]

We used to straighten a lot of fork tubes back in the 70's providing that they weren't too badly bent.
A lot of bikes that just needed new oil seals had a bit of a kick in the tubes.
They weren't bad but they were also not dead true.
We had a milled plate that the fork tube was rolled on to find the high spot and then set up in "V" blocks in a workshop press with a magnetic based dial indicator and we'd straighten them to less than .001" of runout.
It was a bit time consuming at first but after a few you got the idea.
Mick

Nice, .oo1 is pretty good.

Valves can be straightened out with a real similar scheme of v-blocks, and measuring on a bridgeport.

[turboguzzi]

We used to straighten a lot of fork tubes back in the 70's providing that they weren't too badly bent.
A lot of bikes that just needed new oil seals had a bit of a kick in the tubes.
They weren't bad but they were also not dead true.
We had a milled plate that the fork tube was rolled on to find the high spot and then set up in "V" blocks in a workshop press with a magnetic based dial indicator and we'd straighten them to less than .001" of runout.
It was a bit time consuming at first but after a few you got the idea.
Mick

that's pretty much the setup a pro shop would use, so if you shell out a few hundred bucks for a 5ton press, V-blocks and a dial gauge, yes, you can do it at home not sure you'll get them right first time out, experience counts a bit, but hei, each time you crash and bend forks you'll get better
TG

[faux fiddy]

We used to straighten a lot of fork tubes back in the 70's providing that they weren't too badly bent.
A lot of bikes that just needed new oil seals had a bit of a kick in the tubes.
They weren't bad but they were also not dead true.
We had a milled plate that the fork tube was rolled on to find the high spot and then set up in "V" blocks in a workshop press with a magnetic based dial indicator and we'd straighten them to less than .001" of runout.
It was a bit time consuming at first but after a few you got the idea.
Mick

that's pretty much the setup a pro shop would use, so if you shell out a few hundred bucks for a 5ton press, V-blocks and a dial gauge, yes, you can do it at home not sure you'll get them right first time out, experience counts a bit, but hei, each time you crash and bend forks you'll get better
TG

Don't forget the milled plate...

[bwaller]

Worst case if they're bent enough that there is a crease on the backside because of the steel yoke, scrap them. Sometimes they can be bent in two directions as well and this can be tough to straighten.

Otherwise follow mick7504's advise.

[mick7504]

This is where the tubes start getting out of shape.

[754]

DO NOT use Cast IRON V BLOCKS.
 repat do not use CAST v-Blocks..

 most shops that do this work use proper size blocks for several reasons.. I made 15/8 = 41mm and 1 3/8 = 35mm
 Close fit to block is preferrable as any out of round will get noticed..
 You may need more than 5 tons, many good tubes will have to go 2mm or more past straight, to start bending.. and thatt is with 8 or 10 inches between blocks..

 Forks are easy to check against themselves, just hold together, check, turn  (1 fork)1/4 turn, check.. repeat.. Then rotate the other fork..

[mick7504]

That was always the trick Frank, bending them over centre the correct amount to bring them close to true took some patience to get it right.
And a good set of cast steel V blocks.
Mick

[MCRider]

This is kind of off topic. On back of the fork ears on my bike (The area on the fork ears that is directly facing my tank) there are two fairly big sized dents. I've looked at a couple other CBs and they all have these same dents. Can anyone explain? Are the supposed to be there or is it from like a low fork oil issue?

They are there to provide some clearance between them and the tank, when the fork is turned to full lock.

[GammaFlat]

If you (hypothetically) can't straighten them, I'd not consider buying new.  There's plenty of used stuff around.  I see you're in Pittsburgh.  Even if you had to have a set shipped half way across the country, I would think you could get some used ones to your door much cheaper than new.  

Might as well change the seals while you're in there.  

Are you (hypothetically) okay?  Good luck!  

[754]

I would not use cast blocks for pressing.. they are OK for checking though.. There was a tech at a dealership near here, smashed his thumb, when a cast block let go     ...missed work for a while..

  The springback is amazing on high tensile steel tubes..

 The biggest trick on doing them, is keeping an indicator on them during the pressing.. and figuring out the yield point.

 My next bike , gets forks like on that low bike in the pic..

[scrapvalue]

Disassemble the forks and take the bent tubes to a hydraulic cylinder repair shop.
They have to deal with bent stuff all the time and can straighten them with no problem.
I did that with an old 750 Yamaha that I crashed.
Was a pretty cheap fix.

[the technological J]

Disassemble the forks and take the bent tubes to a hydraulic cylinder repair shop.
They have to deal with bent stuff all the time and can straighten them with no problem.
I did that with an old 750 Yamaha that I crashed.
Was a pretty cheap fix.

whats a hydraulic cylinder repair shop? what else do they do?

[MCRider]

Disassemble the forks and take the bent tubes to a hydraulic cylinder repair shop.
They have to deal with bent stuff all the time and can straighten them with no problem.
I did that with an old 750 Yamaha that I crashed.
Was a pretty cheap fix.

whats a hydraulic cylinder repair shop? what else do they do?

They repair the hydraulic push cylinders on heavy equipment like backhoes, dozers, and the like. A motorcycle fork tube is the same as the internal tubes in those hydraulic machines. To such a shop a bent motorcycle fork tube would be childs play.

[GammaFlat]

PM me if you're interested in used ones.  I have a K7 rolling frame. 

[754]

if anyone needs proper blocks made out of steel or aluminum.. I can make them up in sets of 3..

[scrapvalue]

Disassemble the forks and take the bent tubes to a hydraulic cylinder repair shop.
They have to deal with bent stuff all the time and can straighten them with no problem.
I did that with an old 750 Yamaha that I crashed.
Was a pretty cheap fix.

whats a hydraulic cylinder repair shop? what else do they do?

They repair the hydraulic push cylinders on heavy equipment like backhoes, dozers, and the like. A motorcycle fork tube is the same as the internal tubes in those hydraulic machines. To such a shop a bent motorcycle fork tube would be childs play.

Exactly!