Author Topic: It's the little things - forks  (Read 9357 times)

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Offline Steve in Sunny Fla

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It's the little things - forks
« on: January 27, 2012, 02:42:35 pm »
   I'm going to periodically mention some tips that make a really big difference in the outcome of your maintenance regimen. It'll probably be sparked by a discussion that's current, but getting limited exposure.  Here's a couple on forks...

1) if you install a fork brace on a later model, it WILL need to be shimmed. If you don't shim the brace, when you tighten it it will pull the forks together and induce stiction, which will wear out the seals and ruin the forks ability to respond to small road irregularities. The result if that is a stiff, lousy ride. On my bike, it took about an hour of futzing, and it needed .012" shim material to get the brace correctly installed. i had previously installed it without much attention to shimming, and to say that there was a marked improvement in ride quality after shimming would be an understatement.  ETA - aluminum pop / soda cans make great shim stock. Cut them in strips, cans are generally .004" and cut easily with scissors.

2) fork oil. It wears out. also different viscosities will dramatically change the ride quality. Thinner is more reactive as it moves through the damper rod, but may not provide enough damping. Thicker damps better, but may be to harsh. If you want to set up the fork, you may need to try a couple different oil viscosities to get what you're looking for. That leads to the next point...

3) Draining / flushing fork oil - Pre 94's are easy, with the drain holes already in the fork. If you have a post-93, and don't want to remove / drill / tap for a drain hole, there's another VERY easy way to drain or flush. with the front wheel removed, you'll find a socket head bolt extending from the bottom up into the fork. If you have an air impact, you can spin that bolt loose without having to pull the springs and hold the damper rod from the inside. Loosen the bolt, but don't remove it, then remove the cap pn the fork and relieve the spring pressure. Then remove the bolt. The oil will drain, and you can flush the old oil with some mineral spirits and let it drain out the bottom. Spin the bolt back in and finish the rest of the fork service. Too easy.

  I hope these little tips help, I'll post up more as the spirit moves me. and certainly there's a million other little tips, so if you've got 'em, post 'em... HTH, Steve
« Last Edit: January 27, 2012, 07:19:45 pm by Steve in Sunny Fla »
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Offline cal

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Re: It's the little things - forks
« Reply #1 on: January 27, 2012, 02:56:52 pm »
This is some great info, thanks. I'm getting ready for a front tire and this would be the time to do the fork oil.

Offline Liv

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Re: It's the little things - forks
« Reply #2 on: January 27, 2012, 03:13:15 pm »
Sorry, not familiar with the 94 and younger forks , why is there a difference for the need of shimming the fork brace?
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Offline Dave Scott

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Re: It's the little things - forks
« Reply #3 on: January 27, 2012, 03:27:50 pm »
Steve, regarding the fork brace shimming, is that specific to a particular brand?   Mine had a brace installed when I bought it used.  I've had it off and back on for various reasons, but never rode the bike without it.  I'll probably give that a try to validate it's working ok for me, but curious if your shimming need is specific to a brand.  thx....

Offline Bergmen

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Re: It's the little things - forks
« Reply #4 on: January 27, 2012, 03:38:12 pm »
I am in a somewhat tough spot as far as the front forks go. I installed them verbatim from the 2003 ZRX 1200 that I took them from without any maintenance. The previous owner was a stickler about chassis integrity and I assumed the oil had been changed to provide the damping desired. Once I adjusted the compression and rebound damping and spring preload to my liking, the forks performed beautifully. I have no idea how many miles are on the oil that is in there and I also have no idea what brand or type it is or what weight.

When I experimented with fork oils of different weights in the Concours I was amazed at the difference in handling by small changes in viscosity. For me it was easy to experiment since I had modified my forks with drain plugs. The Rex forks are not that simple, the manual specifies a complete fork disassembly to change the oil.

If loosening the damping rod is an easy way to drain the oil on these forks that helps. But it still is somewhat complex for oil weight experimentation. In addition, whatever I drain out is exactly what I want to replace it with since the forks are ideal as is.

Steve, how would you proceed with this?

Dan
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Offline smithr1

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Re: It's the little things - forks
« Reply #5 on: January 27, 2012, 04:32:29 pm »
The way I test my fork brace install is to take it off and sit on the bike several times on and off and have someone measure how much the fork compresses with your weight.  Or as it is known just measure the front fork sag.  Now install your brace.  If it does not sag the same amount you are putting the fork in a bind.  Figure out where and how much shim is needed to stop that binding.
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Offline WillyP

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Re: It's the little things - forks
« Reply #6 on: January 27, 2012, 04:46:11 pm »
This applies to every fork brace regardless of brand or what bike it goes on... EVERY fork brace needs to be checked to see whether it needs shimming, or perhaps it needs the opposite, some material removed. Some may come out of the box and fit without any shims but there is no way to know prior to installing it.

So really what is meant by 'shimming' is more like 'checking the fit and shimming as needed'. DON'T just blindly add shims, just because Steve said his needed 'x' amount of shimming... yours is likely different, due to manufacturing tolerances of the fork brace and of the forks and triples.
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Offline Steve in Sunny Fla

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Re: It's the little things - forks
« Reply #7 on: January 27, 2012, 05:29:36 pm »
Dan - trick question - you have cartridge forks, so no damping rods. did I pass?

  I believe ALL fork braces need to fitted. Think about it  - there will always be small differences from bike to bike. The fork goes betwwn the triple tree and the lower axle. There's alot of places for the clearance to change based on the width at the lower tree / width of the axle. For a manufacturer to try to make it "one fits all" there has to be a method of accounting for differences from one front end to the other. If it were made to wide, it would require machining to remove metal. it's easier to make the fork centers narrower than the average, and the extra clearance is shimmed to fit. Steve
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Offline Steve in Sunny Fla

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Re: It's the little things - forks
« Reply #8 on: January 27, 2012, 05:46:07 pm »
bob - waddya doin - this is all about c-10's only - steve
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Offline Cap'n Bob

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Re: It's the little things - forks
« Reply #9 on: January 27, 2012, 05:50:06 pm »
My bad, it was suppose to go to the C10 tires and suspension section (forks being part of the C10's suspension). I screwed up. I'll fix it now. Sorry.

Offline Steve in Sunny Fla

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Re: It's the little things - forks
« Reply #10 on: January 27, 2012, 05:52:47 pm »
no problem. you're fired. No big paycheck this week. did I do you a favor?  :rotflmao: Thanks for fixing it - Steve
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Offline Bergmen

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Re: It's the little things - forks
« Reply #11 on: January 27, 2012, 06:12:04 pm »
Dan - trick question - you have cartridge forks, so no damping rods. did I pass?

Steve


Hoo boy you got me, I have no idea. Here's what the exploded view looks like:



Dan
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Offline Steve in Sunny Fla

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Re: It's the little things - forks
« Reply #12 on: January 27, 2012, 06:24:05 pm »
Dan - it looks similar to the c-10 fork, but the piece that would be the damper rod is different than the damper rod on the c-10. your forks still have the same bolt holding the fork together, so I assume it can be used to drain the fork also. Time for a visit to zrxoa... Steve
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Offline Carlson

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Re: It's the little things - forks
« Reply #13 on: January 27, 2012, 06:46:54 pm »
The way I test my fork brace install is to take it off and sit on the bike several times on and off and have someone measure how much the fork compresses with your weight.  Or as it is known just measure the front fork sag.  Now install your brace.  If it does not sag the same amount you are putting the fork in a bind.  Figure out where and how much shim is needed to stop that binding.

Is there any other good way to check for binding due to the fork brace? May be measuring the distance between the tubes with and without the brace?..
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Offline Steve in Sunny Fla

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Re: It's the little things - forks
« Reply #14 on: January 27, 2012, 07:13:39 pm »
The way I test my fork brace install is to take it off and sit on the bike several times on and off and have someone measure how much the fork compresses with your weight.  Or as it is known just measure the front fork sag.  Now install your brace.  If it does not sag the same amount you are putting the fork in a bind.  Figure out where and how much shim is needed to stop that binding.

Is there any other good way to check for binding due to the fork brace? May be measuring the distance between the tubes with and without the brace?..

what precision instrument do you have, that can measure to .001" and will spread across the inside of the fork tubes? Why does measuring that way seem more acceptable than checking clearance with shimstock and shimming appropriately? Why make the job more difficult than it has to be? I work with precision measuring all the time, and don't see your suggested method being the best way to go. Just sayin...

   BTW, Rennaissancerider (former cogger) taught me that aluminum pop cans are .004" thick,can be cut into strips  and work great for shimming. Steve
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Offline mike25

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Re: It's the little things - forks
« Reply #15 on: January 27, 2012, 07:21:57 pm »
Is there any other good way to check for binding due to the fork brace? May be measuring the distance between the tubes with and without the brace?..
[/quote]

The best way I've found to fit a fork brace is to remove the fork springs,and cycle the
forks up and down, trying to feel for any binding. Loosening the front axle helps to.

Offline Carlson

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Re: It's the little things - forks
« Reply #16 on: January 27, 2012, 08:14:16 pm »
Quote
what precision instrument do you have, that can measure to .001" and will spread across the inside of the fork tubes? Why does measuring that way seem more acceptable than checking clearance with shimstock and shimming appropriately? Why make the job more difficult than it has to be? I work with precision measuring all the time, and don't see your suggested method being the best way to go. Just sayin...

Yeah.. you're right, did not think that one through  :-[

Quote
BTW, Rennaissancerider (former cogger) taught me that aluminum pop cans are .004" thick,can be cut into strips  and work great for shimming. Steve

Good tip, thanks Steve!
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Offline oldsawfiler

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Re: It's the little things - forks
« Reply #17 on: January 27, 2012, 08:25:08 pm »
SISF and others.
Don't know if this would work here but,  We often measured the distance between feed rolls in the lumber industry by using a "steel tape" and measuring the total distance around 2 adjasent rolls in a couple of spots.  We could get the difference in the measurments down to +- .001 this way.  If the rolls are not parallel it causes all kinds of sawing problems.
Same should be true of forks.
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Offline Bill

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Re: It's the little things - forks
« Reply #18 on: January 27, 2012, 11:11:56 pm »
Some weeks ago, while performing some routine maintenance, I removed the KB fork brace because the little protectors on top of the brace had come loose. I reinstalled the brace and torqued the screws to 15 ft/lbs. Right away, I noticed some fork stiction that hand'nt been there before. Loosened the screws, stiction gone. Experimentation revealed that anything past 8-9 ft/lbs induced stiction, that is by bouncing the front end up and down, not riding.  Some days later, I removed the brace altogether and took a short ride. Front end operated much more smoothly than with the brace. With the crappy weather lately, I haven't been riding, had my mind on other things and haven't done anything with the bike. Anyway, after reading this thread, I went to the garage today and reinstalled the brace. I turned the screws by hand so that the cap was just snug against the tubes and making sure that the center piece of the brace was also contacting the tubes. The gap between the caps and the center piece is a whopping .015" on both sides, that is with two .015" feelers, one at the front gap and one at the rear. It seems to me that starting out with a .012 or .013" shim front and rear would be a good place to start. What is the professional opinion?
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Offline Steve in Sunny Fla

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Re: It's the little things - forks
« Reply #19 on: January 28, 2012, 02:40:01 am »
tighten the brace on one side, and shim the other. The issue isn't  front / back, it's side - side. By tightening one side you've taken all the clearance out of that side, then measure the clearance available between the fork lower and the inside circumference of the brace.That's where the shims go. HTH, Steve
« Last Edit: January 28, 2012, 01:06:37 pm by Steve in Sunny Fla »
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Offline Bill

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Re: It's the little things - forks
« Reply #20 on: January 28, 2012, 10:21:45 am »
Thanks Steve, I'll give it a try.
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Offline GF-in-CA

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Re: It's the little things - forks
« Reply #21 on: January 28, 2012, 06:16:16 pm »
Dan - trick question - you have cartridge forks, so no damping rods. did I pass?

Steve


Hoo boy you got me, I have no idea. Here's what the exploded view looks like:



Dan


Dan,

Your forks are definitely cartridge forks.  I'm pretty sure you don't need to completely disassemble them to change the oil, but you do need to take out the springs, since the oil level is measured with springs out.  On my ZX9 forks, there is a tool you need to keep the spring compressed while you screw the top cap off the damper rod, and my guess is yours are the same.   Race Tech sells the tool, but I made one, and I'm sure you would be able to come up with something once you understand what needs to be done.  It really isn't that bad once you get/ make the tool.  As far as the oil viscosity, Race Tech is a good resource for knowing what is needed, they have data sheets for almost every bike.  The cartridge forks tend use much lower viscosity oil than damper rod forks.  Mine uses 5w oil, for example.

HTH,
« Last Edit: January 28, 2012, 06:20:21 pm by GF-in-CA »
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Offline Bergmen

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Re: It's the little things - forks
« Reply #22 on: January 29, 2012, 02:39:46 am »
Dan,

Your forks are definitely cartridge forks.  I'm pretty sure you don't need to completely disassemble them to change the oil, but you do need to take out the springs, since the oil level is measured with springs out.  On my ZX9 forks, there is a tool you need to keep the spring compressed while you screw the top cap off the damper rod, and my guess is yours are the same.   Race Tech sells the tool, but I made one, and I'm sure you would be able to come up with something once you understand what needs to be done.  It really isn't that bad once you get/ make the tool.  As far as the oil viscosity, Race Tech is a good resource for knowing what is needed, they have data sheets for almost every bike.  The cartridge forks tend use much lower viscosity oil than damper rod forks.  Mine uses 5w oil, for example.

HTH,

Hey thanks, Gary. That is far more informative than if I go over to ZRXOA and act like a newb. I saw reference to the special tool in the manual but I didn't get much farther than that.

This info gives me a good starting basis to tackle this. Thanks again!

Dan
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Offline WillyP

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Re: It's the little things - forks
« Reply #23 on: January 29, 2012, 02:21:33 pm »
To see if the brace needs shims is no harder than measuring valve clearance, as Steve said tighten one side, leave the cap off the other. use a feeler gauge to measure the gap on the side you left the cap off, and whatever feeler gauge fits, that's what you need. Now find a strip of metal the right thickness, a piece from a coke can or buy a piece of shim stock, and cut a strip the same width as the feeler gauge. Or sacrifice the feeler gauge if you don't have anything on hand.

You should also have the wheel and axle assembled to do this. And do a before and after bounce test, sit on the bike holding the front brake, trans in neutral, and push down hard on the handlebars. The bike should bounce back to the same position before and after the fork brace is installed. Not a very scientific test but other than that what can you do? I would imagine you could arrange a scale to test how many pounds of force it takes to move the forks, maybe that would work but unless you are some high tech high stakes racing team I don't see the need.
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Offline Bergmen

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Re: It's the little things - forks
« Reply #24 on: January 29, 2012, 03:39:43 pm »
To see if the brace needs shims is no harder than measuring valve clearance, as Steve said tighten one side, leave the cap off the other. use a feeler gauge to measure the gap on the side you left the cap off, and whatever feeler gauge fits, that's what you need. Now find a strip of metal the right thickness, a piece from a coke can or buy a piece of shim stock, and cut a strip the same width as the feeler gauge. Or sacrifice the feeler gauge if you don't have anything on hand.

You should also have the wheel and axle assembled to do this. And do a before and after bounce test, sit on the bike holding the front brake, trans in neutral, and push down hard on the handlebars. The bike should bounce back to the same position before and after the fork brace is installed. Not a very scientific test but other than that what can you do? I would imagine you could arrange a scale to test how many pounds of force it takes to move the forks, maybe that would work but unless you are some high tech high stakes racing team I don't see the need.

What if the span portion of the brace fits too tight? That was the case when I installed mine, I had to gently tap it into place. The result was a little stiction at first but loosening the axle pinch bolts and working the forks took care of it. If the fit was tighter I would have been out of luck.

Dan
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