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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 24 Aug 2010
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Boing boing: fork springs?

The progressive fixing of long-term niggles in my XT continues ...

Next up, I get an annoying 'boing boing' feeling through the front wheel as I ride along at 100+ kph. It feels like the front wheel is oval, but its not (checked spinning both rim and tyre against a reference indicator). Head bearings are good (new'ish) and tight. I replaced the fork oil, checked fork air pressure, tyre pressure. I have a little super-moto style front mudguard, so that's not wobbling in the wind.

The only thing possible left (it seems to me) is that the fork springs have got too tired and can't control the forks properly any more. They are a *tiny* bit shorter than their service limit figure in the manual.

Anyone else had this problem and fixed it, before I splodge 100 Euros on new springs from Kedo?
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Old 24 Aug 2010
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They're cheaper on ebay

Have never seen or heard about fork springs of the limits.

But the bike deserves it, so consider it anyway.

The handlebar, or the mounts for the handlebar, is rubbermounted. I've heard people say the bike feels weird when they are worn. Could be that.
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  #3  
Old 24 Aug 2010
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Wheel well out of balance?
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  #4  
Old 24 Aug 2010
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hi there i would agree the wheel sounds to be out of balance , have you fitted a new tyre resently and has the problem apeared with the tyre. zigzag
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Old 25 Aug 2010
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It felt the same on the last set of tyres (Michelin Desert) as well as the new Siracs that are on there now. Its true there aren't any balancing weights on the wheel, though. I'll pull it off and check the balance.
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  #6  
Old 25 Aug 2010
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This is not a spring issue. An out of balance wheel would have a much higher frequency at the speeds you indicate. Firstly I would look at the teflon ring on your damper rod and the inner surface of the stanchion for wear. In fact just replace the ring regardless. Next step would be to increace the fork spring oil wt to the next level. i.e. if the bike has 10wt oil in, try 15 wt. This will increace the damping properties.
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Old 25 Aug 2010
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Quote:
Next step would be to increace the fork spring oil wt to the next level. i.e. if the bike has 10wt oil in, try 15 wt. This will increace the damping properties.
Yep - I tried exactly that when I changed the fork oil (motivated mostly by wanting to beef up the handling a bit for my largely on-road existence these days): no difference. Didn't think to look at the teflon ring though, damn. Time to get mucky again, then ...
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Old 25 Aug 2010
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When stripping look for evidence that the oil hasn't been foaming. (i.e. cloudy) If it is it may be indicative that service parts are wearing down.


It might be worthwhile to note here incase this is a new aquisition of yours that the more leggy of the XT's do get a bit like a ship at sea when at high speeds on a motorway. My Tenere would do 85 mph over single track bumpy minor backroads and be solid as a rock while sports bikers were having their martini shaken and not stirred at half that speed. 85 mph on the motorway and every little bit of turbulance or miniscule undulation in the road and I'd start feeling distinctly naseus and wishing I had bicycle clips on to hide the evidence that I was bricking it.
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Old 25 Aug 2010
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Uh oh, special tools ...

Thanks for the input, Bruken, sounds like you know of what you type :-)

Quote:
When stripping look for evidence that the oil hasn't been foaming.
Oh yes, it was super foamy when I changed it. Rats.

Quote:
incase this is a new aquisition of yours
Umm, I've had this bike for 20 years! It's one of those niggles that gradually creeps up on you as things wear out. There's only 85,000km on the bike, but they were all hard, loaded-up, off-road African km!

Lots of questions now!

A squint at the manual reveals "special tools" for taking fork legs apart:

"Hold the inner tube with the front fork cylinder holder (special tool P/N 90890-01328) and T-handle (90890-013101). Pull the inner fork tube from the outer fork tube"

Can I bodge this without special tools?

There's 2 candidates for the "teflon ring" you mention on my explodificated diagram - there's a "Slide bush" (on the bottom of the inner fork leg) and a "Guide bush" (damper rod).

Obviously I'd replace the fork seals at the same time. Anything else while I'm at it? Looks a fairly simple assembly otherwise.
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Old 25 Aug 2010
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On the damper rod itself which with a bit of imagination looks like a piston. On the top there is a teflon ring. Sometimes it is referred to as a bush but mostly as the Damper Rod Piston Ring. Inside the slider there is an oil seal that looks a bit like a flattenned O-ring right near the top. It is referred to as an oil seal (but not THE oil seal and dust seal that embraces the stanchion / fork tube.

When she is apart check the damper rod and fork tubes / stanchion isn't bent. Check the damper rod oil vent holes are clear and haven't worn.

The speacial tool can be made from a 32mm or 36mm (I can't remember which) bolt insert upside down and held in place with a vice grip. You only need to hold the damper rod in place (stop it rotating) while you undo the bolt on the outside bottom of the slider (model dependant). Sometimes it is not neccessary and sometimes if you compress the forks while still on the bike you can preloosen the bolt before removing the forks (tricky to do by yourself)
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Old 25 Aug 2010
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are you sure its just not the geometry of the bike? my xt front end goes very light and flighty when approaching 70/80, and my varadero does it too (but at a lot higher speed, its much heavier bike)

which xt model is it, air forks or just springers?

im assuming plain springers or you wouldve mentioned pumping up the preload by now. if you want to do it with the springs just slug the tops, i did mine about 1.5" and it makes a big difference to roadholding (mines been supermoto'd though, offroaders should keep soft suspension)
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  #12  
Old 25 Aug 2010
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Quote:
are you sure its just not the geometry of the bike
Pretty sure. It didn't used to do this. I tried dropping the forks through the yokes as far as possible (about an inch, before they start to foul the bars) & that didn't make any difference, though I prefer the handling like that, so that's where they've stayed.

Quote:
which xt model is it, air forks or just springers?
'83 Ténéré, with air forks. Yep, tried all sorts of air pressures, back to standard'ish now (10 psi)

The foaminess seems to be the smoking gun: them thar forks are just plain old worn, which is fair enough after 27 years. Now debating whether to put-up-and-shut-up with my wobble, or delve into the innards of the forks (if I can get the b'stards apart!)
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Old 25 Aug 2010
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Taking the forks apart is simplicity itself. Once you have either loosened the damper rods retaining bolts in situ as explained above or by removing the forks and springs and sliding the tube all the way down the slider so you can physically retain the rods while undoing the bolt.

Remove all oil by pumping the shock

Remove the damper rod

Remove the dust seal

Remove the oil seal retaining clip

Now pump the tube upwards so the oil seal bush slams into the oil seal slowly driving it up and out in a hammer action ( note slam upwards but be gentle on the downstroke that you don't bottom the tube out and damage it. )

Once the oil seal is out the bushes and other gubbins will slide out with the tube

DO NOT BE TEMPTED TO MANUALY PRY THE OIL SEALS OUT... They will wedge in sideways and the situation will quickly deteriorate to the point where you start scratching the surfaces and rendering the fork FUBAR.

Goodluck
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  #14  
Old 26 Aug 2010
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The terminology in my manual is a bit different: here's the explodificatedffied diagram.

Terminology in my manual for possible candidate pieces is:

(8) Slide bush
(9) Damper rod ring - this looks like the teflon ring?
(12) Oil lock piece
(17) Guide bush

Next problem is that my Yam dealer doesn't have the micro-fiches for Ye Olde Ténéré, so I can't order parts there! Kedo don't do these spares - any other sources?
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Boing boing: fork springs?-imgp0111.jpg  

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  #15  
Old 26 Aug 2010
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9 yes

The others no -possibly 16 or 17 but they look like bush and washer to me. I'll see if I can load up a photo in the morning.

As for the parts they were cheap enough from the yamaha agents not to warrant looking for alternate sources
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