How To Repair A Bent Frame Tube

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If Y'all are Stuck...

This article describes some ways to repair a steel forepart fork or frame well plenty to become you rolling once more, without access to professional tools.

A alarm: Many of the techniques described here are for emergency repairs merely, and should not be considered every bit permanent or completely safe fixes. These techniques require skill, and are not ever successful. Attempts at repair can cause further harm. Yous use the techniques described here at your ain risk.

But on the other hand, if y'all're stuck 100 miles, or 1000 miles, from a bicycle store, the advantage may well outweigh the risk.

Steel is Existent

Steel is by far the preferred frame material for cyclists who tour into remote areas.

A steel frame usually bends offset, giving a warning, rather than unexpectedly breaking apart.

A steel frame can be straightened (inside limits) if bent, and still remain safe and potent. A welder anywhere in the globe can perform a repair -- perhaps ugly, but safe -- on a steel frame which is damaged and then information technology can't simply exist straightened.

A steel frame tin can remain serviceable with dings, dents and scratches which render a carbon cobweb frame unsafe to ride. Aluminum, titanium and carbon-fiber frames are much more hard to repair, if they tin can exist repaired at all.

My friend John Schubert takes a stand up.

Merely the weight...

Sure, a steel frame may counterbalance a kilogram or so (a couple of pounds) more than a fancy carbon-fiber, aluminum-blend or titanium frame. A bicycle designed to be durable and repairable might besides have other components which are heavier -- but the divergence has a minimal effect on travel time. The bicycle itself makes up simply about twenty% or less of the weight which the passenger must propel upwardly hills. The other eighty% or more is the passenger, -- maybe also baggage. Except when a wheel is heavily loaded with baggage, the added weight will only irksome a climb past only a few per centum, if that. The difference is much less on level basis, where virtually ability goes to fight aerodynamic drag. On downhills, a heavier bicycle is faster!

If y'all ride where a cell phone call will summon your spouse, a friend or a taxi, then feel free to relish the advantages of a lighter wheel. Information technology will have a different "feel" because of the lighter weight and because it transmits road roughness differently. (It could either feel rougher, like many fat-tube aluminum frames, or smoother, like near carbon fiber frames.) If you race, by all ways, a lighter bicycle could get you across the finish line a few seconds earlier, and win the race. I am non ashamed to say that I have a Cannondale route racing bicycle for recreational riding.

Merely, if you ride far from dwelling house, and especially if you ride in places where replacing a cycle frame would be fourth dimension-consuming, hard or expensive, become with steel. Information technology is the choice of Cycle Fri, Rivendell, Waterford and other companies which make high-course touring bicycles.

Also meet Sheldon'south article on frame materials.

At present, onward to specific repairs.

Professional tools

An understanding of how professional frame-alignment tools work can help you effigy out how to perform a adept alignment, or something close, with improvised tools. The image below, from an former Var tools catalog, shows a professional frame alignment table and fork alignment jig. Note: these tools are not for auction at Harris Cyclery, and some of them may no longer exist manufactured by Var.

In the image below, note that:

• Alignment of all parts of the frame is with reference to the bottom bracket.
• Alignment of the fork blades is with reference to the fork crown and the steerer tube, which is assumed to be straight (though it may non be, following a crash -- we'll address that). The steerer tube is clamped and so it can't bend when the blades are being aligned.

Front-end damage

The post-obit comments apply to a bike with a steel frame and a rigid, steel front fork with blades that taper down from top to bottom; not a suspension fork. A moderately aptitude steel fork or frame can commonly be straightened. A crumpled or croaky fork or frame can sometimes be made rideable with a welded or brazed reinforcement. The best repair, except in the case of slight, unproblematic bends, is replacement -- merely in instance you can't...

Fork bent dorsum?

A cycle fork is non designed to withstand an impact from the front. A relatively light bear upon head-on into an obstacle -- a car, a argue -- which pushes confronting the front of the tire tin bend a steel fork backward. The wheel takes the impact the same as the normal weight load, and oft will be completely undamaged.

The fork blades will usually bend back below the fork crown, and the steerer tube will bend inside the head tube of the frame-- a hidden curve, but you tin run into that the lower headset races are no longer parallel. The headset bearings volition probably be loose, or bind, depending on the angle at which you turn the fork.

If the fork is bent back, the wheel's steering will exist heavy, there may be toe clip overlap, and in extreme cases, the front end wheel may interfere with the down tube. If the bend is that extreme, an emergency repair may not be the best idea...

Front end end of frame bent back?

A simple way to right a rearward bend in a steel fork is to plough the fork around backward and slam the wheel into a wall once more -- but that may only farther damage the frame, which may already accept impairment, just backside the caput tube, making the head tube bending steeper. (An aluminum or carbon-fiber frame volition more likely either be undamaged or intermission.)

There used to be a wheel-shop tool which works like an automotive bumper jack. 1 end rests against the wheel'due south bottom bracket and the other has a dummy axle to insert into the forepart fork's dropout slots, or a pipe which inserts into the caput tube. You could improvise a tool similar this with a borrowed automotive jack. You could straighten the fork and frame at the same time, though it is unlikely that everything volition return precisely to its original position. Too, headset race seats may have become distorted, so the races are loose (see communication below), and begetting balls may have indented the races, causing "indexed" steering. Still, may be able to get the bicycle rideable once more this way.

You could insert a piping into the head tube, clench it to something sturdy, and haul upwards on the rear of the frame by mitt.

Moderate heat with a torch helps straighten ripples on the underside of the down tube and meridian tube, though you will damage the paint and -- unless you remove the paint outset, make a sooty stench. Don't use enough estrus to cook brazing. If the tubes are crumpled, you lot may need to braze or weld steel plates to reinforce the joints between the head tube and the other tubes, once alignment has been restored.

Park frame straightener (no longer sold). It is shown straightening only the
frame, without the fork. Thanks to Kurt Kaminer for the photo.

Steerer tube alignment

If the steerer tube is bent, the headset bearings cannot be correctly adjusted. A more sophisticated fork repair is possible in a common metalworking shop, past removing the fork from the frame to straighten the steerer tube beginning, then the fork blades. First, remove the fork crown begetting race. You lot could clamp the fork crown between blocks of wood in the jaws of a bench vise, and use a heavy steel pipe which just fits over the steerer tube to straighten information technology until it is at a right angle to the shoulder of the crown race seat. One side of a carpenter'due south or machinist'south square rests against the crown race seat, and the steerer tube is checked for parallelism with the other side. A metallic ruler also may be used, with its end resting confronting the crown race seat. Lacking these tools, you only try to become the steerer equally straight as you tin.

The bend in the steerer tube will be partway up, just in a higher place the lower section which has thicker walls or an internal reinforcing sleeve. Slide the tube down as far as you can, and so that its lower end rests on the reinforced lower end of the steerer tube and it straightens the curve rather than creating another bend.

The goal here is to get the headset bearing races parallel, so the headset bearing doesn't become looser or tighter every bit you turn the fork.

Cheque the steerer advisedly for cracks. These will be most evident while y'all are applying force to bend the steerer.

Rebending the fork blades

After straightening the steerer tube, I rebent the fork blades with blows of a prophylactic mallet, checking that they were parallel and symmetrical around the extension of the steerer tube. Measurement is the nearly exacting part of this job. Bicycle framebuilders use a special judge to align a fork, as shown in the image from the Var catalog, above. A picture of a homemade fork alignment jig is here . Alignment also can exist checked by placing a wheel in the fork. The rim should sit down equidistant from the fork blades, simply under the fork crown. Turn the bicycle effectually and try information technology both means to check that it is centered, or take an average if information technology is not.

Also check that the dropouts are correctly aligned. A rough test of this may be made with the front hub. A hub with loving cup-and-cone bearings tin can still be functional with a bent axle and misaligned bearings. If the beam and dropouts have matching misalignment, but both announced intact otherwise, you could ride to the next wheel shop at some modest chance. Checking for dropout alignment is described in some other file on this site.

Too see Jobst Brandt'southward comments on bent front forks. He describes a way to marshal fork blades which are bent to the side, without whatever tools other than your own easily and feet!

Fork bent forwards

If the front end wheel has landed heavily on a horizontal surface, the forepart fork may be aptitude forward. This is an extremely dangerous bend. With one paw on the handlebar, the steering will tend to weave because the feedback from the handlebar is aberrant. If both easily are removed, the front end wheel will all of a sudden turn to the side, throwing yous forward over the handlebars.

Usually, the frame will exist undamaged. Considering the intersection of lines extended from the down tube and head tube is more or less directly over the hub axle, a vertical touch on does not produce large bending stresses on these tubes!

Fork bent to the side

A fork besides tin be bent to the side, or i fork bract can exist aptitude dorsum more than the other then the cycle is tilted. If you ride through water, the cycle tracks of your wheel should form a unmarried line. If i tire track is off to the side of the other, the fork (and/or the frame, run into below) is out of alignment. And so you have to lean to one side to proceed the cycle upright, if you can ride at all without hands on the handlebars. The tire may rub on a restriction shoe or fork blade. And if the fork is aptitude to the side, the frame also may be twisted...

Adjustment a Frame

If a bicycle pulls to the side, the front end and rear of the frame -- not only the fork -- should be checked. The bike will not runway properly unless all of these parts are in alignment.

If the front triangle -- and front fork -- of a cycle frame are aligned correctly, the front wheel will rails in line with the rider.

Correct alignment of the rear triangle is also necessary to place the rider's weight directly over the wheels. If the rear triangle is aligned correctly, then the chainline at the cranks and at the rear hub will likewise agree, and the the chainwheel(s) and rear sprocket(s) volition be parallel.

If all of the parts of the frame are in alignment, and the wheels are centered, it will exist possible to ride the wheel no-easily. That is the msot stringent test of a bicycle's alignment.

The front-triangle misalignment problems described below are in the order in which they need to be corrected, only the issues closer to the bottom of the listing are more common. Then, you may be able to do a quick check and skip several steps.

Frame tube visibly bent in the middle but non crumpled?

For the seat tube, down tube of top tube, yous could drill out a wooden block to the same diameter as the tube, and saw it in half. Place one half confronting the side of the tube and tap information technology with a hammer, increasing forcefulness until the tube is straightened. Sheldon describes this technique in his article about his Raleigh International bicycle.

Here'south another image from the Var catalog showing a tool to realign seatstays. This tool applies the opposing force to the seatstay either side of the curve, reducing the tendency to change dropout alignment. I've succeeded with a length of angle iron, wooden blocks to avoid scratching the pigment, and C clamps. The dropout alignment should be checked anyway -- come across below.

Seat tube out of line?

As described to a higher place, all parts of a bicycle frame should be aligned with reference to the bottom bracket crush.

Alignment starts with the seat tube. It is unusual for the seat tube to exist aptitude, but if it is, information technology must be realigned first. To check, yous could place a straightedge against the confront of a chainwheel running upwards next to the seat tube. The straightedge should be equidistant from the meridian and bottom of the seat tube. Rotate the chainwheel 180 degrees, check again and take the boilerplate in case the chainwheel is canted. You could also identify the straightedge along the side of the seat tube to check for a bend.

For the acme end of the seat tube to exist hauled to one or the other side, the bottom-bracket trounce has to be clamped securely. Framebuilders do this piece of work on an alignment table every bit shown above, just I have succeeded by clamping the faces of the lesser bracket shell firmly betwixt wooden blocks in a large bench vise, inserting a pipe into the seat tube and pulling the piping to the side.

One time you have removed the crankset to clamp the bottom-bracket shell, you can't utilise the chainwheel for measurement any more. Simply on the other paw, you will rarely find that the seat tube is bent.

Downward tube aligned to bottom subclass beat?

The same procedure applies here as with the seat tube.

Forepart triangle twisted?

The forepart triangle of the frame may twisted and so the caput tube tilts slightly with relation to the seat tube.

Defective a frame alignment tabular array, you could stand in front of the bicycle and sight along the edge of the caput tube to come across whether it is parallel to the seat tube. Placing a straightedge aslope the head tube makes whatever twist easier to visualize.

Realignment is with a pipe inserted into the head tube, while holding the bottom subclass clamped. The top tube will tend to move more because its diameter is smaller. If you lot pull on the pipage higher up the superlative tube, you lot volition tend to move the top tube sideways more; if you pull on the pipe beneath the downward tube, the downwards tube more,. If y'all have already aligned the downwardly tube, you want to make your adjustment at the top tube. The sideways adjustment to make the needed adjustment in the angle of the head tube is small, considering the head tube is short, but yous might want to go dorsum and check the downward tube and seat tube, only to be sure.

Rear end lf the frame bent sideways?

Testing and correcting alignment of the rear end of the frame is accomplished as described in the article on this site virtually frame spacing.

The you do this with a length of cord, a ruler (or even only a stick where y'all tin mark lengths) and a wooden plank.

Testing rear-triangle alignment with a string

Crumpled, stripped, broken...

Onward...

Headset bearing seats distorted?

Moderate baloney of bearing seats and so they no longer hold the begetting races in a press fit is easily stock-still with "plastic steel" -- epoxy glue with embedded steel particles. Minor looseness can be addressed with blue threadlock compound. Either of these materials can be broken autonomously later by a accident to the bearing race, and scraped off, so a new race can exist installed.

Before the material hardens, the headset should be adapted, the bicycle ridden and the headset readjusted, so equally to seat the races.

This is not necessarily only an emergency repair. I have performed it in the class of routine rebuilding.

It is sometimes possible with professional cycle shop tools to manufactory the bearing seats to accept a different begetting race press-fit size.

Fork threads stripped?

Replace the fork, or if yous can't::

• Cutting downwardly the fork steerer and splice in a replacement from another fork. This may also be unthreaded, for utilize with a threadless headset and clamp-on handlebar stem. (unlikely, though, that these parts volition be handy for an emergency repair...). See information about splicing, beneath. The splice needs to be depression plenty to permit insertion of the quill-type stem which is used with a threaded headset, only otherwise the higher, the ameliorate considering stresses are everyman near the tiptop of the steerer tube. This repair is not practical if the steerer tube is curt.
• Remove spacers, and so you can re-engage the threads. Or, cut down the top of the head tube, but this can only be done well with a professional bicycle store tool, and the bicycle shop probably tin can sell you a replacement fork.
• Use plastic steel to secure the headset locknut, merely then don't await e'er to go it off unless yous burn off the plastic steel with a torch.

Bottom-bracket threads stripped?

This problem is virtually likely to occur when working on the bicycle and is much more likely with an aluminum-alloy frame than a steel ane. The classic repair is to rethread the lesser-bracket shell to the Italian dimensional standard -- ane mm larger in bore than the others -- but this requires professional bike-shop tools and Italian-standard bottom-bracket parts. Some bottom-subclass shells do not have thick enough walls to allow the rethreading. A Velo Orange threadless bottom subclass offers some other solution. If but one side is stripped, you could secure the bottom-bracket cup on that side with plastic steel -- aforementioned removal outcome as with the headset locknut, only worse.

Dropout bent or broken?

If the rear derailer gets caught in the spokes, the right rear dropout may exist aptitude or broken. If it is only bent, information technology can unremarkably be bent back into shape. Heat from a torch tin make this chore easier, but don't apply enough heat to melt brazed joints. For one time, an aluminum frame may offer a simpler repair: the derailer hanger is often a bolt-on role.

If the derailer is pretzeled, the classic repair, is to shorten the chain and ride the bike every bit a singlespeed.

Modest dents

Don't worry near these. If you lot tin access the inside of a tube, you could run a length of pipage (for case, a seatpost), into the tube to push out a dent. A professional framebuilder may apply metal blocks, drilled out to the bore of the tube and sawed in half, and then clamped over the tube. Because the margins of the dent are raised, clamping the blocks down may button the dent out. Pressurized h2o inside a tube besides could remove a dent, but that gets rather high-tech...

Deeply bent, crumpled or cleaved frame tubes

If a frame tube is crumpled, you might straighten it and so reinforce it. Brazed or welded steel plates can reinforce joints between tubes, once alignment has been restored. A welded or brazed-on reinforcement can splice the ends of a broken or crumpled tube.

The image at the left shows a frame tube prepared for splicing. Paint has been sanded off either side of the joint. The within of the tubes to exist spliced also has been sanded make clean. A length of tubing has been cutting lengthwise and then it can be compressed and slid into the spliced section as a reinforcement. Small holes take been drilled where brass can be practical and will menses into the joint.

If you are far from a welding shop, you might splint a crumpled tube, for example with automotive hose clamps and a length of angle atomic number 26. The tube must nevertheless be able to take a load in tension, so a splint is reasonable if the tube is crumpled, but non broken. The tension and angle stresses on a chainstay, or any part of the front end fork, do non allow of splinting and clamping, though I once did manage to ride dwelling house on my Raleigh Twenty with a right chainstay which had rusted out from the inside and cleaved. That was on a non-derailer bicycle and the concatenation held the chainstay together.

The prototype at the correct shows an ugly but strong weld to the forepart fork of my married woman's recumbent cycle. If non for this repair, the plans for our wheel bout would have been completely dashed. Another article tells the entire story.

Replacing frame tubes...

A steel frame can exist repaired by replacing a frame tube outright. This is sometimes washed to restore a historic or valuable frame, but may also be done just to get a frame back on the road. A trashed frame tin provide the needed cloth. I repaired the Raleigh Twenty frame I mentioned earlier past brazing in the chainstays and chainstay bridge from a trashed frame.

Maintaining right dimensions is important in this work. With the Xx, I left the seatstays and rear dropouts still in identify, and I clamped a dummy rear axle into the dropouts to concord them in alignment.

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