Beefing up a CBR Clutch

[zoomzoom]

does anyone know if its possible to beef up the clutch in a CBR600?
just wondering if there is any way to make it take a bit more punishment as we have to ride ours pretty hard to get the car off the line.
thanks.

[zoomzoom]

does anyone know if its possible to beef up the clutch in a CBR600?
just wondering if there is any way to make it take a bit more punishment as we have to ride ours pretty hard to get the car off the line.
thanks.

[Lyn Labahn UW-Madison]

I am not aware of any "homebrew" modifications that you could make to the clutch itself, but there are a variety of upgraded springs and clutch disks that motorcycle riders outfit their bikes with. The internet would be a great place to start looking, as well as your local motorcycle parts shop.

Just remember though, it is often advantageous to have the clutch as the weakest point in your driveline. A snappy, indestructable clutch can shock load tranmissions and driveshafts so badly you break them with ease. Perhaps consider changing your driving style a bit, before trying to make up for finesse with brute force.

2002/2003 Team Leader
Best overall average finish of the new millenium http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Mechanicaldan]

Barnett is probably one of the most well known manufacturers for heavy duty clutch friction plates and springs. From experience the heavier springs will tire the drivers grip quicker, and the clutch may become grabby.

Unless you know you are having a problem, I would just suggest changing the oil more often.

Motorcycle clutches will take a LOT of abuse before wearing out. Most street bikes will go 30,000 miles before needing new fiber clutch plates. I have two close friends with '92 F2 and '94 F2. Both have over 40,000 miles, and only one has replaced a clutch. Both have drag raced their bikes. My 900RR has over 30,000 miles on it, and when I finally did need to do clutch work, I found the fiber plates were perfect, and the springs simply needed replacing. They were 1/8" shorter than they should have been. My RR has had the oil changed every 4000 miles. Castrol 20W50 in the summer, 10W40 in the winter.

Here's some good reading that was sent to an email list I'm on from a professional engineer and weekend motorcycle racer that is involved with our college motorcycle club, www.isumc.com (http://www.isumc.com)

"Hi guys

I'm getting a lot of useful tidbits from your exchange, thanks for the
info. I too have used Mobil 1 in all my racebikes over the years. The
only bike I can think of that had a problem with Mobil 1 was an FZ750,
the starter sprag immediately ceased to function once we added Mobil
1. We tore the engine down (of course, the sprag is buried inside) and
found nothing wrong with it. On reassembly, we tried conventional oil
on a hunch, and the sprag worked normally again. I guess the Mobil 1
was just too slippery for it. (metal-on-metal sprag clutch)

Wet clutches are a different beast. They do not wear like you would
expect- there should not be a significant amount of material
(contaminant) lost into the oil. In fact, wear in a wet clutch is a
sign that things are being pushed beyond their ideal condition. (which
does happen, especially on hard launches)

I'm not a mechanical engineer, but I do play one on TV. ;-)

On engagement, when the clutch is still slipping, the oil film becomes
so thin between the steels and frictions, that it ceases to act as a
lubricant- the molecules align like a bunch of logs in a row, and it
essentially becomes rigid. Above 50 angstroms in thickness, oil acts
like you'd expect, it shears like a liquid btwn the slipping plates.
As distance btwn plates closes to 50-30 Angstroms, shear resistance of
oil shoots up 1000 to 10,000x (as the molecules align) The oil shears
like a deck of cards, in layers. At around 20 Angstroms, the oil
becomes nearly solid. As sliding velocity approaches zero, very little
oil is left in the interface, and static friction initiates.

In an ideal world, the clutch plates do not touch when sliding. wet
clutches in industrial applications can run endlessly, slipping away,
with oil doing all the work . Of course, they are sized properly and
have immense quantities of oil to work with. Dry clutches, obviously,
contact and wear and slip just like you'd envision.

A bike clutch is generally sized as small as practicable and does not
have a very large safety margin.

In a bike, there are ways to defeat the happy clutch. Flat, parallel
plates are the key to a nice clutch. Warpage of any kind creates spots
of extremely high local pressure- that pressure digs thru the oil layer-
you get plate-to-plate contact.. and material wears off. Excessively
high facing pressures (killer springs) can squeeze all the oil out from
btwn plates while they are still sliding- and again, you get contact.

You can warp plates by dumping heat into them faster than they can shed
it into the oil- too much heat, and they will warp. Clutch steels have
a certain amount of mass that allows them to store heat energy, like a
reservoir, and shed it into the oil after the launch is done. A dry
clutch has to shed heat into the air- EXTREMELY inefficient. that's
why they are so much easier to nuke on a start, than a wet clutch.
either scenario, too much heat in the steels and they will deform, and
they're done.

Friction plates that have been roasted by slippage and/or too-high
spring pressures can become compacted/hardened, and lose their ability
to retain oil. Once this happens, they are junk. No amount of sanding
will bring them back. They can be perfectly flat, and perfectly shot.
Replace frictions if you are at wit's end (or before).

Finally, extremely high sliding velocities

BTW, as sliding velocity approaches zero, there is often a roostertail
(torque spike) - IOW, a grabby clutch, or stick-slip behavior
(chattering) Friction modifiers (as I read it here) do their work in
this region, to suppress the torque spike and make a clutch that
transitions from sliding friction, to static friction, without a big
lurch right at the end.

Oil that is not intended for wet clutch use -- I guess it just wouldn't
need those friction modifiers. I suspect that they do not increase the
torque capacity of a wet clutch, I believe they DO make a wet clutch
much more pleasant to live with. If Mobil has recently eliminated this
stuff from their automotive oil (ie not recommended for wet clutches)
and jacked up the price of their bike oil, that's our loss, I guess. I
don't know how important those modifiers are, let's face it, you can put
in about any generic brand of car oil and get decent performance in a
bike clutch. I say this based on lots of experience, as an old fart who
has owned and ridden lots of bikes.

Anyhow. Unless you beat the hell out of a clutch, it shouldn't be
shedding a lot of stuff into your oil. Race launches count as beating
the hell out of a clutch, tho... Change oil every race weekend if
you're serious, and use the best filter you can find. No amount of oil
additives will "fix" oil with a lot of junk floating around in it. And
if you are getting a lot of clutch debris in the oil, might want to make
sure everything in the clutch is flat and true.

NO, I don't have this stuff memorized, I'm reading it off a text on wet
clutch and wet brake operation.

I had some comments on all the special bike blends, but I just deleted
them. I can't speak intelligently on a topic I know nothing about-
hmph! However, I suspect marketing plays a heavy part in the
proliferation of 'niche' oils. Just like coca-cola selling 10
different varieties of flavored water, for god's sake (!!)


Randy N!

TL1000S - currently running whatever oil I found on the shelf in my
garage- I believe it's a mix of 3 types, actually.... at least one
bottle was Mobil-1! A consequence of a 5 AM pre-departure clutch swap..."

Mobil 1 does now sell a motorcycle specific oil.

Cyclone Racing
www.cyclone-racing.com/fhome.htm (http://www.cyclone-racing.com/fhome.htm)
Iowa State University
Engine Team Leader