Steer tube straightening help

[Schwinny]

Before I try a couple of my own first thoughts, is there a tried and true way of straightening a fork steer tube?
One of the fork arms was twisted a bit also, but that straightened real easy in the the vice with a little twisty pulling.
So far my ideas are to press an appropriate size iron pipe all the way down the inside of the tube. Or to put the same size iron pipe in as far as it will go and in a vice pull on the forks evenly at the head.

I'd rather not ruin this fork any further or throw it in the scrap pile so I will defer to experience if anyone has any tried and true methods.
??
Thanks.

 

[ricobike]

The best advice for this is to apply the same force in reverse as the force that bent it. The little brute fork jack does this very well. If you can find someone close to you that has one, that would be my suggestion for the best method. There have been some creative ways discussed in this forum as well. You might try a search for fork straightening in this forum to see some other ways you might try.

 

[bloo]

I have done it, but I have no suggestion of an easy way. The advice about doing the exact opposite of what made the bend is very good. How to do that is tougher. I can see a lot of reasons the Little Brute might just make a mess of that, but I cant lie, If I had one here I probably would have tried it.

First of all, take the crown race (lower) off. Get a nice perfectly straight aluminum ruler or a machinists rule and sight down it. You will need to miss the bump at the bottom where the crown race presses. Figure out just exactly which direction the bend is in so you get the angle exact opposite angle when you pull.

Support the inside with something most of the way down to the bend. I used a 21.15 seat post on one fork, but yeah good luck finding one, and your fork might not be that size internally anyhow. Don't bend with that from the inside, you'll fishmouth it. Clamp it in something like a frame block in a vise, down close to the bend but not THAT close. Pull on the fork. Go slowly and judge whether your block and pipe are in the right place. You might have to keep moving it as you unbend. I kept checking it in my friend's lathe, but had to go across town each time (lots of times). I know not everybody has a lathe laying around. I was turning it by hand and marking the spot so I would know the angle to pull when I got home. The lathe only gets you close. You cant clamp on the fork tube enough and far enough out to not hurt it and still see everything, so there will still be some bend. Once it looked perfect in the lathe, on one particular fork I had to re-cut the seat for the crown race a little. In any event, make sure that seat is true.

Then I assembled it in the bike, tightened the bearings to zero clearance, and turned the fork all the way around. If you get your eyeball right up at the top cup you can see exactly WHERE it is still bent a little and the cup got closer to the cone. By closer I mean up/down if the bike were sitting upright. Mark it, take it back out, and bend a little more until it runs true. Repeat as many times as necessary.

OK that method might work if it is fairly weak steel. The good news is many are. If it wont unbend though, you might have to just shrink the high side with an acetylene torch a few times.

Once the headset runs true, then you can deal with the fork legs. You can figure out huge front/rear/twist problems by laying it on a flat surface. To get the bike to go straight is much harder. You need it mounted in a frame you have checked and know is NOT bent. Put some handlebars and a seat on, pad them against damage and put the bike upside down, Get the handlebars straight ahead, the fork crown straight ahead, the bearings at zero clearance, and the bottom bracket perpendicular to the ground with a level. Put long threaded rods with washers and 4 nuts each where the axles go. Mind the OLD of the hubs. Run strings right against the nuts from the front to the back, and measure to the bottom bracket or seat tube. to see right/left errors in the forks. Remember we are talking about a frame that has been VERIFIED straight. For/aft errors can be seen by measuring the distance front to rear (wheelbase) on the threaded rods right next to the nuts, while the fork crown is pointed perfectly straight ahead. Take the threaded rod out and and bend as necessary.

Or you could send it to somebody who fixes forks and keep your sanity......

 

[kreika]

I believe @Krakatoa does fork straightening?

 

[tacochris]

If I personally was going to do this repair, I would secure the fork solid upright, find something to put around the threads to protect them during the straightening process. Find a pipe that is just a tad bigger than the steering tube, apply generous heat to the bend and then gradually bend the fork tube straight using the aforementioned pipe.
With a long enough pipe and the right amount of red heat it shouldnt take super strength to get it back correct

 

[Schwinny]

All great thoughts and ideas. Best part is that I sit back and think deeper about the geometries and circumstances. Also, with the pic I posted I now see a wrinkle that isn't apparent at first when focusing on the steer tube.
The bike it came off was completely stoved up, everything from the fork and wheels to the crank, and even the brake calipers were frozen solid. Even after soaking and heat, I had to tap the steer tube out of the head with a wood block and dead blow hammer. The front wheel hub and rim were slightly skewed but not terribly twisted. The frame itself didn't look damaged. The head where the steer tube is bent looks straight, the head badge is flush. Strange.
This bike and several more were high in the rafters of a storage building for decades. Here in AZ., they spent a lot of time at temps above 150 degrees and more. All those bikes have been problem children.
Now Im thinking about wether its worth it for future use or for practice in straightening stuff like this.
I'll need to distance myself from my expectations I guess.
Im no stranger to metal fatigue so I might take one try at it, real close to the scrap pile so I don't have to throw it very far.
Thanks much for the encouragement and ideas.

 

[bloo]

Well, Schwinny I am straightening another one. I truly am a glutton for punishment. The 53 Huffy I am working on had the steer tube bent in a curve. Not quite as bad as yours, but still a big obvious curve. The fork crown is also bent. I am basically on the long winded program I described above.

I now have the steer tube bent close enough it looks good when chucked in a lathe. The crown is untwisted enough that the fork legs appear to be in line with the steer tube when laying on a table. However there is still a little bend in the steer tube. With the headset assembled and adjusted a little too tight you can see it. It doesn't show up that well in the picture, but if you look closely you can see the gap is wider at the bottom of the picture than the top. it is fairly obvious when you turn it. I am either almost there or I over-corrected slightly. Just a tiny bend now and the steer tube will be completely straight. It may take me 2 or 3 tries....

Then the forks will be straight down to the bend in the legs. Below that, one side is curved more than the other. I won't really be able to do anything about that until the bike is partly together and I can measure it. I really should take my own advice LOL!

 

[Schwinny]

Well, Schwinny I am straightening another one. I truly am a glutton for punishment. The 53 Huffy I am working on had the steer tube bent in a curve. Not quite as bad as yours, but still a big obvious curve. The fork crown is also bent. I am basically on the long winded program I described above.

I now have the steer tube bent close enough it looks good when chucked in a lathe. The crown is untwisted enough that the fork legs appear to be in line with the steer tube when laying on a table. However there is still a little bend in the steer tube. With the headset assembled and adjusted a little too tight you can see it. It doesn't show up that well in the picture, but if you look closely you can see the gap is wider at the bottom of the picture than the top. it is fairly obvious when you turn it. I am either almost there or I over-corrected slightly. Just a tiny bend now and the steer tube will be completely straight. It may take me 2 or 3 tries....

View attachment 1419963

Then the forks will be straight down to the bend in the legs. Below that, one side is curved more than the other. I won't really be able to do anything about that until the bike is partly together and I can measure it. I really should take my own advice LOL!

Nice work, the satisfaction of putting it back the way it started and rolling a bike around that sat for decades on the edge of misfortune is a great feeling for me. I love to pimp an old bike around that hasn't rolled in decades. I imagine you will be there real soon.
As for my fork..... that one..... not so much
It was one of those French forks off an early 60's Schwinn Continental. Semi-lightweight and of thinner and of a higher tensile strength originally. I made a wood block to hold it, and a machinists straight edge tight in the vice. Then I turned the steer tube into a huge resistor with house wall voltage. When it got to 450 degrees (about 10 seconds), I unplugged the voltage and pulled gently in the appropriate direction and it went straight pretty easy.
It looked pretty good and I was checking how much more I needed when I noticed the metal had cracked and separated in a crazed fashion on the inside of the previous bend.
With that and the wrinkle lines on one of the arms, I decided enough was enough. Theres no telling what the years of heat in the rafters did to the metal structure. Thinking about it further, it may have needed to stay at a high temp for quite awhile before being straightened... hard to say right off hand. But I sure couldn't trust it after that.
So..... there's one way and one circumstance where I'll know better next time.
I really appreciate all the help and ideas.