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Moderating: Fair & Just
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Discussion Starter · #1 ·
If you were to rock the forks, and result was they're bent.
My thought is that it's possible the bend is somewhere in the triple tree and not in the forks themselves.

On one hand, part of the triple tree looks to be made out of some sort of cast iron (I could be completely wrong on that point) and wouldn't bend very much before it just cracked. Of course this wouldn't apply the neck of the triple tree.

On the other hand, the leverage involved with the forks would suggest the much higher likelihood that it would be a fork or both of them that are bent. (At least that's the way it looks to me)

On the 3rd hand 馃槃, I don't think Kawasaki cheaped out on the construction of these forks. The first time I took them off I was pleasantly surprised at what the quality looked like to me. (Of course this could just be me)

Regardless of what is bent, I'm not suggesting the fix would be any different than what is described in
this thread> Forking Around: A Fork Maintenance Guide
Although I'm guessing if you can actually see something bent with the naked eye, then it's time to start buying parts.

This is really nothing more than something that has just sparked my curiosity.

Thoughts?​
 

Fast Old Guy
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the triple trees bend easily part of rocking the forks is to determine if the are bent or just twisted. in any case the trees are eassilly straightened i believe i wrote the process how to tell and fix

Fog Merry Christmas
 

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I've successfully straightened forks that were not too severely bent (i. e. not deformed to the point they are kinked). What you need is a hydraulic press to apply very controlled force and some aluminum saddles of the right diameter to support the tubes so you don't damage them further. Its tough to get them to zero runout but if you can get 'em to within a few thou they seem to work fine.

Not likely you could bend the lower tree without bending the forks as well. I think the lower trees are forged and thus way less brittle than cast.

Merry Christmas to all. I was hoping for a brown Christmas but things didn't go my way, lol.
 

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The time I bent forks, the lower triple was also bent...forks/stanchions? can be straightened but my mechanic friend who has the tool said "No!" for mine..my example is apparently beyond the safe limit and would make a crease and otherwise weakened if starightened.
Wood Grey Wall Automotive tire Font
 

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Yeah, your example looks to be what I'd call on the ragged limit of what is salvageable. If you are paying for someone else's time(starting with making a set of custom saddles), you have to compare with the cost of new. Its a fussy job and will never be as good as brand new (or even used in good shape). But sometimes with vintage bikes availability is zip so you gotta do what you gotta do.

In my experience, frontal impact starts with bending the stanchions just below the triple, then the triple itself, then the stem (where the lower bearing sits inside the head) ,and finally the frame. So just because you manage to get the triples to line up doesn't mean you are out of the woods.
 

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Too true, Datsun...I managed to "ebay" some stanchions and then discovered your truth... (luckily I had a parts bike with a better triple tree)

The triple tree looks so solid! but I know now it is not. The trail "out of the woods" can involve some long detours and I can see why the insurance wanted to just write a bike with any front end damage off as a wreck rather than long work-orders involving rare parts and labour for an old and rareish bike. (CB450SJ) But I did get it back on the road and still ride it.
 

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After my get-off in 2017, I pulled the forks and checked them on a surface plate. One was straight and the other I could barely slip a 0.0015" feeler gauge under. Reassembled, rocked the forks and it did not ride straight. Pulled the triples and the lower was bent. It is pretty soft stuff. Had a spare which I painted and slipped a new tapered roller bearing on. The upper was fine.
 

Fast Old Guy
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The lower tree can easily be straightened it is malleable iron
clamp the stem in a strong vise and fit the tubes to the lower onlytighten the clamps then try to fit the upper tree you can see how the lower is bent. Use the fork tube as a lever to bend the lower back into alignment with the top tree. A little heat from a propane torch will help.

Fog
 

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The lower tree can easily be straightened it is malleable iron
clamp the stem in a strong vise and fit the tubes to the lower onlytighten the clamps then try to fit the upper tree you can see how the lower is bent. Use the fork tube as a lever to bend the lower back into alignment with the top tree. A little heat from a propane torch will help.

Fog
Will do. Fortunately, I have a surface plate as a second check for parallel when done.
 
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Moderating: Fair & Just
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Discussion Starter · #12 ·
I would think using a fork tube for bending the triple is the best option. Not just for convenience. Using a random smaller diameter pipe may run the risk of tweaking the clamp area of the triple out of shape.

I vote for stick with the "perfect fit" fork tube. (y)
 

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As usual, FOG nailed in post #8. Tightening the clamp once the stanchion has been slid in ensures the hole stays round as you apply leverage to straighten the tree. The stanchions are comparatively stiff and the tree is fairly easy to twist once its disassembled from the top triple. If the amount of force seems excessive, that's where the heat comes in.

While everything is apart take a very close look at the stem down by the bottom bearing. If it was a hard enough hit the inner race will have kinked the stem and the assembly will never really be right.
 

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A salient point here is that my fork tubes stayed straight while the cast iron triple was bent. And that was from a quick impact which multiplied the force used - the tubes were used as a lever to bend the lower triple. Slowly, and as FOG says, with a reasonable amount of heat, there is no risk using those carbon steel tubes to tweak some soft iron back into place.
 

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Check what tube you have left for straight. If you have enough to run from lower to upper tree, you have nothing to lose in using it. Pull the tubes from the sliders - certainly the lower end of the tubes are straight.
 
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