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There's a previously owned 2009 YAMAHA FZ16-S that I'm thinking of picking up. It has a slightly twisted and bent fork (plausibly caused by an accident). It's only apparent when you ride it for a bit. Upon pressing down hard on the front suspension, one can see faint amounts of oil on the fork legs (seal compromised?). I've taken it to a few mechanics who have confirmed this.
I believe it can be fixed by taking it apart and straightening it with a hydraulic press.
Though the cost of getting this done is measly, I've gotten varying opinions from different mechanics on the degree of success for this operation.
The integrity of the frame and safety is paramount to me and I intend on riding this bike over long distances.
I would like to know the details of the fork-straightening process (whether there are different approaches and procedures?) and general recommendations for carrying out this process/discern if it's beyond repair.

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    I doubt you'd be able to straighten it correctly or well enough to fix the seal leaking. You may be able to pick up a used set of forks on ebay (other auction sites are available) or alternatively you could purchase a set of fork stanchions only (the chrome parts) and get them replaced. – Mauro May 20 '15 at 12:28
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    Personally, I'd steer well clear of it - if you know it has been in an accident and not repaired properly, what other damage might have been caused and missed? cracks in the frame etc... – Nick C May 20 '15 at 12:31
  • I'd make this a long and irrelevant and hopefully amusing answer if I had the time. I haven't so herewith a short and irrelevantish comment in lieu |. Long ago on a (not Yamaha noy FZ16) Jawa (!) failed to take a gravelled mountain road corner and hit a safety fence. Fork end bent right off axle (pinch bolt onto knobless end.) Remove fork. Hitchhike into next town. Borrow gas set. Heat and hammer etc straight-ISH. Hitchhike back. Reassemble. VERY twisted - but "rideable". Proceed to off road valley and spend 2 days trail riding. Set out for home - about 100 miles. Mostly there and a cop ... – Russell McMahon May 20 '15 at 15:22
  • ... flags me down. Tut tut.Dangerous unrideable etc. Issues special notice declaring bike unfit to be used on road. "A long time since I've had to issue one of these' he says. Relatively affable - but he also issued me a ticket for driving vehicle in unfit state to be on road. On return wrote and told story - told of 2 days trailriding etc. Maybe some photos. Noted it was actually quite safe despite looks as my story demonstrated. They agreed ! - and let me off. I think I wrote the bike off for parts :-). | So - The FZ16 'should be fine" [VBG]. (Yes. The story is true). – Russell McMahon May 20 '15 at 15:27
  • @NickC great pointer! Thankfully I have the bike for a few days for inspection – chilljeet May 21 '15 at 5:14
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Fork Straightening

Process

  • The slider and internal oil valving are removed.
  • The stanchion (inner fork tube) is placed on v-blocks
  • A dial indicator is used to detect deflection as the stanchion is rotated
  • Once deflection is understood a hydraulic press is used to bend the stanchion back to its original state.
  • The process of measurement and bending with the press is repeated until a minimum amount of deflection can be detected

Risk

The stanchion has been repeatedly straitened has undergone enough stress cycles as to degrade the integrity of the tube. This, obviously, is undesirable. This can be detected by lubricating the tube slightly and running your hand up and down the tube to detect anomolies in the surface. Any surface anomolies on the stanchion will result in ongoing fork seal issues. As the fork seal passes by the surface anomoly it will quickly degrade the seal or allow oil to pass by resulting in oil leaks that can effect the brake rotor or tire surface which, in both cases, could prove to be a safety issue for the rider.

Opinion

I've personally straightened many stanchions at shops and at home with excellent results. Another avenue for remediation is to simply replace the stanchion AND the plain bearings within the slider.

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  • Yes your oil seal is broken , get than fixed asap.
  • Fork Bending on the FZ-S is a very common issue , though its a 43mm fork it bends quite easily, so slight bend might have caused due to driving fast onto a pothole or an accident as you say.
  • There are two things you can do for this situation.
  • Yes you can fix it but it will be still noticeable(if you know someone who does it then it might be close to perfect else you will still have a small bend) These slight bends wont affect your everyday riding much and definitely should not cause any safety issues since its not a fast bike.
  • If you are extremely concerned and want a perfectly straight handlebar then either you have to be friends with the guy with the hydraulic press or ignore this bike.
  • As for how the fork bends are removed , different shops use different machines for example most(Indian) shops use a rudimentary hydraulic piston with a pivot and a manual inspection of the forks by straightening slowly , this is the cheapest way to do and thus causing less precision.

Edit: I would also consider replacing the entire fork set which would solve this whole issue once and for all.

  • This was great info. And yes, I've noticed this with the FZ16's among the few people I know who've owned it. – chilljeet May 21 '15 at 5:01

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