Shortening a Hayabusa front end, and Intro.

[Mullins Chaindrive]

Hello,
Brandon here.
I have been lurking for a while on the board. I am building my first LSR bike here at my small shop at home. A 650cc Blown Fuel Streamliner. The motor will begin as a 1956 BSA A10. More to come on the progress and some build pictures. JackD was kind enuff to come out to the house and discuss a build strategy and some fundamentals for this project. And no sooner did I get started that I already have some questions.

I am using an '06 Hayabusa inverted front end, no different than most late model street bike front ends Im told. However, I have never taken anything but Harley Davidson/SHOWA type front ends apart before. I am planning on taking the fork legs down to reduce the overall front end height. I have the tubes stripped down and the dampening rod assemblies out.

My question for the Hayabusa guys or anyone else thats been in this boat: has anyone ever shortened a fork like this? I am running a 17" wheel with a typical Goodyear front slick, so I will need to eliminate approx 5 inches of unwanted fork travel.

From what I can gather, the spring may remain uncut, but the lower cartridge assembly that houses the piston will have to be shortened and re-threaded. In addition, I believe the outer sliders will have to be cut and sectioned to allow for travel as the distance from the bottom of the lower tree to the top of the wheel is about where I want ride height just as the sliders bottom out on the axle drop outs.

Im worried that the dampening rod may crash into the bottom of the fork tubes if I eliminate too much of the lower cartridge.

Wow, a mouthful for my first post. Im looking forward to being a "productive" member of the board and hope somebody besides me has opened this Hayabusa fork flavored can of worms....

[firemanjim]

You could ask the folks over at www.suzukihayabusa.org
or maybe Mr. Noonan has some insight.

[Jonny Hotnuts]

Most of the guys I have seen strap their fronts or extend the forks above the triple tree ie:



I have never heard of anyone shorting the fork leg itself....but I bet it can be done.

[Mullins Chaindrive]

Thanks for the replies.
There are a few posts on the Hayabusa boardon the topic of shortening a front end. Ive sent some PM's. As far as strapping and lowering the trees, that would definitely bring ME closer to the ground. The idea here is to decrease the overall size of the forks to get the top of the liner closer to the ground.

Brandon

[Xea]

I bet if you called Frank's Maintenance & Engineering (Forking by Frank) at (847) 869-6792, they could help.

[Mullins Chaindrive]

A good idea, I have used them in the past for Harley stuff, SUPER NICE people and very reasonable prices, BUT, sadly they don't build an inverted fork tube and had no leads for anyone that does.

[MadDuck]

You might want to consider a standard front fork setup for land speed racing.  Springs and oil are much quicker to change and time is critical on the salt. 

I doubt very much that an inverted fork will help for your application.  Especially if you have  knowledge of other forks.  Go with what you know, first you can always change it later.

[greg]

Ought to be able to get 5' by chopping the top of the dampener rod assy and rethreading it. Usually about 7mm or something weird with a 1.0 thread pitch. Either throw away spacers or chop spring depending on stiffness/sometimes both a bit.

[stayt`ie]

i would advise against dropping the forks through the tripple tree, and straping, as this method decrecess rake (if you dont drop the rear end) just what you dont need for high speed stability.

i have internally shortened my zx12 forks by 3", and i really dont see that the hayabusa forks would be that different that you couldn`t shorten them also, although 5"

it would be pretty hard to explain how to do it in words, my advice would be, pull the fork leg apart and think about it, if you have ever shortened `ole school forks, it`s sort of the same principle, but in reverse, sorry if this sounds confusing, but...

along with the spacers you will have to turn up, you will also have to shorten the internal springs by the required amount...

best of luck, it "can" be done

[Jonny Hotnuts]

In looking for some hayabusa go fast stuff I ran across a guy in Indiana who says "Get rid of your lowering straps. We can modify your forks to your application. Shorten, Stiffen, and insert bump stops, or make them solid if you choose"

http://www.dragbikedirect.com/services.php

Dont know anything about them but the web site sounds get on my nerves but it looks like they are not a fly by night organization.

[donpearsall]

I shortened my 'Busa forks so now they are lowered and have about a 2" travel. I bought a lowering block kit from Schnitz and did all the work myself. Believe me, it is a royal PAIN, and takes a while, as well as makes a huge mess. You have to have several special fork tools or make your own. If you don't have a well equipped shop and are not an experienced mechanic/machinist, I would not recommend it. Also the instructions that came with the kit leave a lot to be desired.

Don Pearsall

[Mullins Chaindrive]

Thanks guys,
As far as using a typical Harley fork, in hindsight it may have been a more practical choice. I was kinda caught up in the "trick factor" and quality of the Hayabusa stuff. For the price I couldnt refuse. I also thought the inverted fork design and overall width (witch is wider than harley) would be a plus as far as stability. Overkill, probably.
Im confident I can make them work. I went ahead and called the guy over at Dragbikedirect.com, pretty knowledgable guy. He has worked on LSR stuff before and knows a few guys on here. He was very helpful and ready to listen. Most guys are only willing to read off part numbers and wont hang there neck out if it means trying something new.
I have the means to do the work myself here at home and I work at West Coast Choppers in Long Beach, so we have a pretty comprehensive facility here. The time issue is what I cant compromise. I think I might send the set out to the guys at Drag Bike Direct. From a practicality standpoint, it seems smarter, huge metric tap to rethread fork tubes and inner cartridges? special tools to tear down the dampner assemblies? Sounds like an expensive learning process. Usually I'm game for doin it the hard way, but I think Im gonna box them up and send em out. Thanks again for the info and the link guys. I'll let you know how they turn out!

Brandon

[Larry Forstall]

THE man for shortening inverted forks is Terry McIntosh at http://www.mcintoshmachineandfabrication.com/ Cost is a function of how much is done since the dampner rod is easy to shorten but the external tube requires cutting and internal threading etc. They can be made any length and they come with fresh fluid ready to install. They do very high quality work, you won't be disappointed.  L

[kiwi]

I shortened mine up with no problems. It's just a matter of measuring and working through it methodically. I will post what I did later on today. I got to go to work now.

[kiwi]

-Cut outer tube to desired length. I took 3 1/8" off mine which left 1 1/16" parallel section left for the top clamp. This would be the maximum you would want to take off here. May even want to leave a bit more on to give you more scope for adjustment in the trees.
-Recut thread and O ring seat.
-Cut the stanchion (inner tube) so that it clears the fitting that screws in the top of the outer tube (top nut)by 3/16". It will be a similar amount to what you took off the outside. Be aware when cutting these things that the stanchion musn't come out of the top bearing at full droop.
-Make a urethane bump stop 1/2" thick that sits just below the top nut.
-Get the damper tube and tape the inner rod to the outer at full extension. This is just to stop things moving around and also keep the swarf out when you turn it.
-Turn the swage off the hydraulic bump stop (the alluminium tapered thing on the inner rod)
-Now you can take the circlip off that was under the swaging and remove and throw away this stop.
-Cut the rod to get the length desired and rethread. This length will determine how far the stanchion will come out. Note that there is a spring built into the damper that will extend a bit (approx 1/2") under full droop.
-Put in shorter harder springs. I have some if you need them.
-Make new tubes to preload the springs the desired amount.
-Shorten the thin solid rod which slides in the centre of the damper rod for adjusting rebound damping.
-Assemble everything to the top nut.
-Assemble staunchion in outer and put cap screw in the bottom of the leg.
-Put oil in (I used 15W).
-Screw on top nut.
I hope this makes sense. It is a little hard to explain. Just work through it and you will find it fairly straight forward.