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The Hayabusa Clutch: Part 1 of 3
Monday, September 05, 2011 Paul Cavanaugh

Why this whole article came into being…

I have been trying to get a 250 hp turbo Hayabusa to run an 8 second ¼ mile since 2008. (Korry Hogan once told me to put Jeremy Teasley on it. Problem fixed.) Granted it has not always had that much hp as I have gone through some major learning curves in the development of homemade air filters, figuring out the finer points between a clutch slippage and 2nd gear going out, having a turbo header break and now failing clutch components.

This year the bike has made the most horsepower it ever has. Unfortunately I had not been able to race it for the first half of the year because I was waiting for parts to come in during the rebuild process and then the turbo header broke. Once finally together, I took it to Test and Tune to get ready for the 2nd half of the Atlanta Dragway NHRA point’s series.

On the 1st pass the bike stood straight up in the air, I chopped the throttle and got back on it as soon as it was coming down only to launch it off the ground again, both tires, when I twisted the throttle again. I just chalked it up to being rusty on a high horsepower bike as I had been borrowing stock Hayabusas for the first half of the season.

On the 2nd pass the bike literally leapt from the ground, not once but four times. Every time it came up I pulled the clutch in a bit to slip it, as soon as I pulled the clutch the RPMs went through the roof so I let it out just a hair and it would leap into the air again. The back tire left the ground leaving 4 distinct patches about 3 feet from each other.

I almost had to clean my leathers out after this pass and now can fully identify with what a bronco rider goes through.

On the return road I started trying to slip the clutch from a standstill to see if it was just me. The clutch just grabbed and killed the engine as soon as I started to let it out. I tried it again and it started bucking once again when I started to ease the clutch out at 2,000 rpms. Something was definitely going on in the clutch area.

This is my adventure on how to fix this problem. I will cover all the performance clutch set-ups including back torque eliminators, billet baskets, billet hubs, single stage lock-ups, multi-stage lock-ups, sliders and how they supplied a solution to this issue.

The Clutch’s special purpose

Without this mechanical component forward locomotion in a regulated manner would be nearly if not entirely impossible with any combustion engine driven vehicle.  (I know; someone is going to write to me about CV transmissions…)

A clutch has two main purposes; firstly, to apply engine power to the drive train without killing the engine from applying too much load at one time and secondly, to allow the engine load to be disengaged to allow down-shifting or up-shifting. (It could be argued its other purpose is to piss me off as described earlier.)

 In the case of a clutch for a manual transmission as found on the Hayabusa, it is our job to slip the clutch in order to move on down the road from a standstill. In drag racing the clutch is a significant factor between a great 60’ and low ET… or a run you hope nobody witnessed.

How does it work?

It is rather simple in fact. The main players of parts found in the clutch department are as follows:

1.      Input shaft
2.      Clutch basket
3.      Hub
4.      Back torque eliminator
5.      Clutch fibers and steels
6.      Springs
7.      Pressure plate

There are a few other parts also, but these are the major ones.

The crankshaft has a drive that turns a gear attached to the base of the clutch basket. The clutch basket fits over a caged bearing on the input shaft to your transmission. It is called an input shaft because this is where the power from the crankshaft is converted into rotational energy for your transmission. By itself the basket cannot drive the transmission. Since it spins on needle bearings it just freewheels without the help of the other components.


Hayabusa clutch

Hayabusa clutch


The next part to help things move along is the clutch hub. It fits on the input shaft. It has three cogs in it that fit into the back torque eliminator. The back torque eliminator has splines that match the ones on the input shaft. This item, along with the hub is what directly turns the input shaft, although they need another item to help.


Hayabusa clutch

Hayabusa clutch

The clutch fibers and steels fit onto the hub within the clutch basket. A fiber goes on first alternating from there out with steels and fibers. You will notice the fibers have tabs that stick out and the steels are round with cogs in the middle. The tabs on the fibers are driven by the clutch basket; the steels drive the hub when the clutch pack is compressed together. This brings us to another set of components.

Hayabusa clutch

Next the pressure plate is added to the hub and six springs are installed in the pressure plate. This is what supplies the static pressure to compress the fibers and plates together when the clutch handle is released. (Spring pressure only. This will be an important discussion later.)On the Hayabusa, the static pressure from the factory is around 240 lbs.

Hayabusa clutch

In a nutshell here is how it works together. You are holding the clutch in at a traffic light. The light turns green and you ease out the clutch. This allows the pressure plate to slowly compress the fibers and plates. As they do so, the hub slowly starts to turn driving the input shaft which in turn drives the output shaft causing your front sprocket to turn the rear wheel and you are off to your destination.

Now think about what you are doing at a drag strip… The bike is revved up to 6,500 rpms, the light changes, the clutch is thrown almost all the way out, because you want it to slip some and all of the clutch fiber tabs are slammed into the billet basket as the steels are slammed into the hub. If everything went right, you are not sitting on your ass looking down the track as your bike is flipping through the air, but instead you are rocketing towards a great ¼ mile.

Back Torque Eliminator (BTE for short…)

Its main purpose is to prevent the back tire from locking up during aggressive downshifting. It is made up of two parts and it accomplishes this by actually allowing the torque eliminator part to jump over the the ring which locks onto the three protruding studs in the hub I described earlier. This action in effect causes the input shaft to still turn without locking the back wheel and causing an inopportune slide in a curve.

Hayabusa clutch

Hayabusa clutch

But who the hell is using a Hayabusa in a curve to begin with?

At the drag strip the BTE is just a part to scare the crap out of you when you throw the clutch and you hear it start making a chunking noise as it tries to lock into place from your abrupt take off.  You’ll swear the first time it happens that either your chain is jumping teeth or your transmission just deposited a pile of metal into your oil pan.

Fortunately there are numerous ways to do away with this component.

You can try and weld it together on your own if you are intent on destroying your entire clutch assembly. I am not saying it can’t be done because someone had done it to my bike when I first bought it. But it is not an easy process unless you have developed a jig to do it correctly. Even after doing that you need to make sure it is balanced so your entire assembly does not vibrate or wobble.

Personally, I would buy one from Brock’s Performance like the one shown, as you know it is going to work. Other companies make them also and by getting one it allows you to use a stock type clutch hub which can be purchased for less than the billet hubs.

Hayabusa clutch

Another option for bikes that start hitting the 250 hp range is getting a billet clutch hub which eliminates the BTE components completely.  I’ll get into these in more depth in the next installment.

Paul Cavanaugh
Coming up next…
Billet Baskets and why you need one.
Billet Hubs and why you need one.
Single stage lock-ups.

See ya at the track…
- Paul Cavanaugh

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