Rear end of frame slightly bent

[JHNguyen89]

I bought a KDX220 a couple weeks ago for a great price. I'm new to dirt bikes so I honestly didn't know (and still dont know much) about dirt bikes other than it being able to run and start easily. That being said, the previous owner whom I bought it from seemed very honest and helpful about things. He mentioned that he had a fall awhile back and messed up the rear fender. I thought that'd be a easy fix, so I bought a new fender, though, when installing it, I noticed it's a bit bent in the back.

Should I be worried about this?

<img src= "http://i418.photobucket.com/albums/pp269/smellmypeebody/DSC_0434.jpg?t=1261120409">

 

[Patman]

Why worry aboit it? Straighten it out or buy a replacement. It's pretty common.

 

[mideastrider]

Have someone sit on the bike or strap it down and slide a long pipe over it and bend it back. Not a problem.

 

[mathd]

If you plan on not changing it(wich is not a problem) make sure there is no crack.

 

[BSWIFT]

Why worry aboit it? Straighten it out or buy a replacement. It's pretty common.

Might not be the only time it gets bent.

 

[weav6385]

I personally would straighten it. Its very easy. Get a map gas or propane torch and heat it up where you think it bent at. If you cant see the bend just ask yourself (where would I bend if I were a subframe?) The answer will be obvious. Heat up, push back into place, paint, and enjoy. Good luck.

 

[Patman]

No need to mess with a torch. It bent without heat so it will bend back without it. Besides you don't want to have to mess with painting it. You might also look in to an aluminum replacement. They tend to be less prone to getting tweaked.

 

[weav6385]

Heat is your friend. It took alot of pressure to bend that subframe. If you heat it you can bend it back with very little effort. Then you will have a fresh paint job on half your frame which im sure it could use anyhow. Either way will work but I'm just sayin from experience heat makes everything easier.

 

[Patman]

Heat can also make it more brittle. A piece of brittle metal is more inclined to break rather than bend. A broken piece of metal can be quite sharp and that of course is bad for skin as well as anything else it might come in to contact with. A long lever of some kind should be plenty. If you are familiar with how metals react to being heated and actually know how the properties of the metal you are working with will be affected then by all means knock yourself out.

 

[weav6385]

Actually if you have ever bent a piece of metal back and forth cold what does it do? It breaks. If you heat up the molecules they dont resist as much. They then cool and create a new "memory". Do what you want either way will work. You will not make the metal "brittle" any way you do it. Good luck.

 

[Patman]

How about our new resident expert give a complete and detailed play by play on how to properly heat, bend and cool the metal to insure it is not left in a too ductile nor too brittle stage? Unless the OP has the tools and knowledge to work with metal they are better off effecting the repair without possibly making the situation worse.

The fact of the matter is that very few people are going to pull out a torch and heat up the subframe to bend it back. Some will not worry about it, most will just bend it back cold (not wiggle it back and forth until it breaks DUH!) and a few will use heat. Of those that use a torch most will have a piece of metal that is too brittle compared to the adjacent un-molested metal because they cooled it too fast with a splash or rag full of water. Professional certified welders actually understand the metallurgy and that is the value of using them vs. many of the home hacks with a torch and buzz box.

I should add in most instances the subframe is really twisted as opposed to being bent and that appears to be the case in the attached photo. Same fix.

 

[High Lord Gomer]

As long as the tire does not hit the subframe nor the silencer, I wouldn't worry about it.

 

[Ol'89r]

If you heat up the molecules they dont resist as much. They then cool and create a new "memory". .

IMO, you should NOT heat your sub-frame. It is very easy to destroy your sub-frame if you don't know what you are doing with heat. If you heat it a little too much you will wind up with a soft piece of aluminum that will bend every time you put a little pressure on it. The material will not go back to it's original condition ("memory") without being heat-teated. Concentrate the heat on any one spot for any length of time and you will have a puddle of aluminum on your floor. Some aluminum alloys will melt at just a little over 1100 degrees.

Like others have suggested, just hold it down and bend it back into shape. It's not rocket surgery or nuthin'. :coocoo:

 

[Porkchop]

If it was easy, every one would do it.....

If it's made of aluminum, here's the list of several methods. If it's made of steel, disregard all of the heat related procedures & do what ever is necessary to get it back in good shape. Assuming it's aluminum, the hoop over the wheel well should be partially annealed due to how deformed it is, prior to reforming back to original shape. Remove the paint on the hoop first. Annealing is done by using a pure acetylene flame to blacken the hoop & the rear of the tubes only. Then adjusting the oxygen on the torch to a neutral flame & warming the hoop carefully from the center out until the black soot clears up. This happens between 700-800 degrees f. caution, do not over heat, do not stop the flame from moving continuously whilst heating , a waving motion works best for this. As soon as the soot starts to clear up, move on , do not dwell on any one place, or hold the end of the flame to close to the work piece. Stop when progress has been made to about 1/2 " from the welds on the seat rest tubes. On some bent parts, only the severe bend it's self, need be annealed. Allow to cool slowly. Some improvised but simple tools are a big help for doing the job of straightening & reforming & are easy to make. A body working hammer dolly is good for the seat\wheel well hoop. A strong back or strong steel table is good for clamping the sections of tube needing straightening. I use a block of maple with a vee cut on the end(push block) & a hammer for shocking the part where needed, in the direction needed. I use other maple blocks, stacked & clamped as required for support when clamping prior to shocking with hammer & push block. Avoid striking any tube directly with a hammer, hit the push block with the hammer with the push block on
the tube. To straighten a twisted sub-frame, strip all parts off, then with it bolted to the chassis, use a long lever (2"x4"x6' works well) to torque it back as needed. Hammer, preload with clamps & shock as needed until original shape is obtained.
Do not anneal any tubes, connection points, or welded junctures. Re-aging can be started by placing entire part in a oven set at 400 f for 1 hour duration, then allowing to cool to room temp slowly (wrap in heat blanket), wait 3 days before part goes back into service, Or pack in dry ice for 24 hours after a day at room temp.(temper #'s on aluminum range from 0 to 8, 0 being soft, 8 being hard, these directions will yield between #3&4 temper). On some parts I do this several times, ( new pieces, not sub frames) it toughens the material. As always, safe practices must be followed in all this & caution must be taken seriously. It is always best to have a professional welder-fabricator do this, but for the do it your selfer, there it is. If any or part of the heating or re-aging/ tempering procedures are omitted or deviated from, scrap is the result, or the part will be too soft & bend easily.( more scrap) I express or imply absolutely no guarantees on any of this info.
A word to the wise, You be your own judge, A small to moderate repair, fix it.
A moderate to mangled repair, expend Ben Franklins on a new one.... :think: Patman, you requested this..... always happy to share, PC.

OL 89'R's recommendation of using a temp-stick is excellent advise, once again ,"cheap insurance". Also, for the first timers that have the guts to try doing any of this, practice on a piece of scrap 6061-t6 or 5052-t4 aluminum, prior to attempting a repair on your frame.
If a decision is made to buy a replacement, consider a part made of titanium, yes the cost is more but it's way more durable than aluminum, lighter than steel & 4 times stronger than steel & includes some major bragging rights. (if you're a crasher like me the more durable part is a priority).

 

[Rooster]

Uhhh, yeah. Grab a 2 x 4 and un-tweak it. Go ride.

 

[Ol'89r]

Uhhh, yeah. Grab a 2 x 4 and un-tweak it. Go ride.

:laugh: :rotfl: Good one Rooster.

Great post porkchop. May I add one more thing.

If anyone is thinking about using a torch on aluminum , go to your local welding supply and buy a 'Templstick'. These are little crayon looking things that melt at different temperatures. If you want to anneal your aluminum, you can buy one that melts at 800 degrees and it will tell you exactly when you reach that temp. As mentioned, it is critical that you do not overheat aluminum since it will melt at just a few hunded degrees above the point of annealing.

 

[Porkchop]

If that sounds over complicated.....

Rooster's method is one of my favorites. It's quick & simple & quite ok.
Each time this method is used on aluminum, the zone that's getting fixed gets harder. The 3rd or 4th time the cold/lever method is used, it's only a matter of time until things will start to fracture, so look out for it.
2 years ago my services were requested to help repair a then new Ferrari 360 gtb. The owner experienced a "cell phone incident" & a power pole jumped right out in front of the guy's new car. The body & chassis are all constructed of aluminum. The chassis is 3 large castings, the front (trunk, suspension, etc.), the middle(passenger/ crash capsule, doors, etc.), the rear,(engine housing, rear suspension, etc.) all tig welded together, very nicely.
The crash damage was localized to the front right corner, luckily. It required 13 annealing procedures to get the front right side of the casting back into museum quality condition. Then we fitted the front & right new quarter panels,that by some miracle we managed to procure out of ferrari ( ferrari does not like to sell parts like that to any one but their dealers). When we were finished ya could not detect that a wreck ever happened, even by looking inside the wheel well, at the suspension or chassis. The moral of this story, HANG UP, PAY ATTENTION & DRIVE! $25,000 for the repair, on a car worth a quarter mill. :bang: :nener: :think:

 

[FX]

Good advice Ol' Buddy

 

[Patman]

Patman, you requested this..... always happy to share, PC.

That's pretty much what I was looking for. To show what a complicated procedd it is to do with heat properly vs. the brute force with a lever method. Thanks!