84 fork shortning

[chiz]

Hi I am hoping some chaps out there may have some answers. I want to cut a couple of inches off a pair of 84 FJ fork tubes and have the internal threads re-cut I was asked by the folks that are going to do the work if the tube was specially hardened?
Also the springs will have to be cut and can not think of how this would effect fork action or even if the same amount of fork oil should be loaded?
  Also I had not planed to shorten damper rods, I know that shortened rods essentially have the same overall shortening effect as tube cutting, but I have not an iota of knowledge as to how any of this will effect actual damping?
  Thanks Chiz 

[red]

Hi I am hoping some chaps out there may have some answers. I want to cut a couple of inches off a pair of 84 FJ fork tubes and have the internal threads re-cut I was asked by the folks that are going to do the work if the tube was specially hardened?   Also the springs will have to be cut and can not think of how this would effect fork action or even if the same amount of fork oil should be loaded?    Also I had not planed to shorten damper rods, I know that shortened rods essentially have the same overall shortening effect as tube cutting, but I have not an iota of knowledge as to how any of this will effect actual damping?
  Thanks Chiz

Chiz,

Man, that's a lot of re-work, and it's a one-way street.  Why not just loosen the fork tube clamps, and raise the tubes in the clamps without any cutting?  If the hydraulics are in the way, you could use clip-on handlebars, attached near the tops of the tubes, so the hydraulics can stay at the same height, just above the tubes?    The handlebars may get a bit higher, depending on the clip-ons that you choose, but that may not be a bad deal, there.  When it comes to lowering the front end, a little goes a long way.  Just a thought.
.

[chiz]

Yup I follow your reasoning for sure the raised tubes in yokes are the way I have them now. For the reason of not going into a long winded why I don't want to go this rout is why I have chosen to go with cutting the raised tubes.....spoils the look I am going for.
Thanks Chiz

[gdfj12]

Chiz, going with the tubes raised in the triple clamps would seem to be the most practical way to go, as it allows reversal of the mods. If you go with cutting the tubes shorter, you'll have to re-tap to be able to put the fork caps back in. Then you need shorter springs and just cutting the ones you have down will actually increase their effective spring rate because the rate is affected by the free length, outer diameter, wire diameter & material properties of the spring. You will also be significantly affecting ground clearance, especially when cornering.

May I ask what your purpose for doing all of this is?

George

[fj1289]

If you want to actually shorten the forks, there is a MUCH EASIER, TRIED AND PROVEN METHOD!

Internally shortening the forks is very common.   You disassemble the forks, add a spacer on top of the top-out spring, and them reassemble the forks.  Typically you will reduce the preload spacer by the same amount (or a bit less) of the shortening spacer you've added.  

Chris

Adding a link - sure there are others

https://www.youtube.com/watch?v=OoMQtK4M42M

[Old Rider]

Not sure this will work on a FJ if you lower that much, the cowling will smash into the front fender when braking hard or hitting a bump in high speed.
the bike will also be very under steered and the rear wheel wants to come up on your side when braking and braking into a turn.I think you have to
lower rear end of bike to and then there is very little ground clearance left.Here is a pick of the fork fully compressed

[fj1289]

Internally lowering the forks will not change how much the fork compresses.  All it does is keep them from extending as far.  But, raising the forks through the triple clamps will allow the wheel to come closer to the lower triple clamp or the fairing.   

[chiz]

Ok interesting reply's all forks and yokes are going on a different bike which had a much shorter fork but much less stout. I will go over all of this and pick the best option. But the forks need to be shorter so yes seems you guys are giving me some options. Now I got to figure out how I'M going to replace that little fuse box cover on the dash that took a powder somewhere on a nice long ride today
Thanks Chiz

[FJmonkey]

Anyone 3D print the fuse cover yet?

[Sparky84]

Anyone 3D print the fuse cover yet?

You got bookfake? Monkey

They printed some back a few months

https://www.facebook.com/groups/1414088652227511

[Sparky84]

May I ask what your purpose for doing all of this is?

George

I'd like to know Why also 

[aviationfred]

On my 1990, I have the RPM valves installed and the Racetec springs. The springs and valves were in when I purchased the bike, with the springs being very over sprung. My guess would be .95kg or 1.0kg springs. In an attempt to soften the front end, I have reduced the spacer from 4 inches to 3 inches. The result was a bit softer, but this also lowered the front end dramatically. Fortunately the stiff springs keep the fairing from contacting the front fender during hard braking. In the following photos, you can see how low the front end is. In the second photo, you can see that my fingers are NOT on the brake lever, collapsing the front end.

Fred

[chiz]

All motorcycles were designed with varying length's of front suspensions which had to "fit" the design of the rest of the package. The package "bike" that the FJ forks will be going on need to be shorter to emulate the length of original components but provide a facility to mount discs etc etc. I have a pair of forks front end.... it's just the shortening bit that is posing a bit of an issue.
   The short stroke diving issue is not an issue at all as there is no faring for the fender to hit
  Thanks

[fj1289]

Chiz - sounds like a great upgrade for another bike - what is it?  A cafe project?

I'll emphasize again that damper rod forks have been shortened with an internal spacer for years (decades!).  This is one of those times where the easiest, least expensive method is also the safest.  



Add a 2" long spacer at the red arrow.  Reduce the preload spacer at the blue arrow by up to 2" (I'd start with an inch or so and then trim more as needed).  As an alternative - to adjust the spring rate - you can cut coils instead of shortening the preload spacer.  

There is no change at all to the internal workings of the fork - the spacer merely restricts the fork from fully extending.  It does shorten the total travel by the amount you shorten them - that would be the only draw back.   The FJ forks are about 5" of travel - so that would be reduced to about 3".  Since it sounds like it is going on a smaller, lighter bike and it sounds intended for more performance oriented use, 3" should be plenty of travel.  You may get lucky and the too soft for an FJ fork springs may be perfect for the new bike.   If they are still a bit soft you can always trim some of the tighter wound coils off and add to the preload spacer as required.  

Cutting a coil spring increases the overall spring rate.  On a progressively wound spring - the tighter wound coils are the softer rate and are the ones you'd want to cut.  

[chiz]

Thanks....69 R3  All original bits are carefully restored and stored and not thrown away. Chiz