Dry Clutches for Motorcycles

Fabrico · Apr 26, 2006

Hi,
What ever happened to dry clutches for motorcycles? I raced and maintained CZ motocross bikes which had dry clutches for years and never saw a worn clutch. Also had a Triumph with a dry clutch, worked great. Although they are a tad heavier and for sure more expensive, they can be just as compact and durable as a wet clutch. Some major roadrace machines also used them. Anyone use them now?

ctmtwilliams · Apr 26, 2006

They are still around on high end road bikes like Ducati.

thundair · Apr 26, 2006

They are dry on my Guzzi 1100 sport and my belt drive conversion Norton and on my Ducati Monster

Cheers

Tmoose · Apr 28, 2006

Some CZ enthusiasts are going to the trouble of converting to wet clutches. Greater smoothness is mentioned as one of the subjective advantages.

Fabrico · Apr 29, 2006

Although wear was not really a problem, there was notching of the clutch basket and mashing the edges of the drive plate tangs. Both seemed to be from rotational hammering.

As I recall, the friction plates were a somewhat heavy bronze plated steel with impregnated lube. This left a very thin steel section to engage the basket. This, and perhaps the fact that it was a 2-stroke, seemed to be a bigger source of problems over that of lubrication.

They can't be too bad if thundair is running 3 of them!
Thanks for the replies.

LadaTrouble · Apr 30, 2006

My wife used to have a Harley Davidson/Aremachi Sprint 350 SX,that was the trailbike version.They had a dry clutch,but the cover was sealed - and every few months the clutch would get grabby and shudder.You had to pull the cover and strip the clutch,blow out the dust and deglaze the plates.You could vent the cover,but then water would be able to get in.I didn't think it a was good idea.

R1100S · May 2, 2006

Ducati, BMW and Moto Guzzi all use them. They work well, but are easier to abuse than wet clutches. Wet clutches require special oil and have parasitic loses.

R1100S · May 2, 2006

I shouldn't say special oil for wet clutches. Just different oil. In a dry clutch bike any automotive grade oil will do just fine. In a wet clutch bike the friction modifiers make the clutch slip more than it should so you need motorcycle specific oil without the additives.

Fabrico · May 2, 2006

Well that raises other questions. My Honda CR500 (60hp dirtbike) uses a wet clutch and 85wt gear oil. The clutch never slips or anything. BTW, it uses aluminum drive plates with friction material added. Pretty much bullet proof. Never was aware of special or different oils but then again maybe all the MC trans lubes have it.

drwebb · May 23, 2006

Gear oils don't usually have friction modifiers. Put in some Dexron III/Mercon ATF- or better yet Chrysler ATF +4 for a more conclusive comparison.

timmgold · May 25, 2006

As far as the notching on the clutch basket, that's a common problem. I recently rebuilt an FZR600 with this issue. I just filed the grooves on the basket smooth and it worked fine. Not the most elegant solution, but it made the the engagement action much smoother.

Regarding the use of ATF, you can't do that in a motorcycle engine as the crankcase and gearbox share the same oil.

drwebb · Jun 5, 2006

All 2-stroke performance motorcycle engines and most Honda off-road 4-strokes utilize separate lubricants for the clutch and gearbox. I wasn't suggesting the ATF as a substitute for the motor oil but for the gear oil.

Now that you mention it, non-FM ATF might work pretty well even for the shared sump on a 4-stroke combined box motocross bike since these typically have about a 4-hr change interval.

Cr250r · Oct 17, 2006

Hi there

I race a CR250 and use Atf for the gearbox, ( not the F/mod one of course !)

Its good for ONE ,,MAX two races and gives a nice(r) clutch feeling ,

The 06 /07 bikes have a lighter clutch ( unless the display model didnt have any internals!!!~)

I am in the middle of modding my bike to get a reduced lever feeling ( these modern tracks are hard without a light clutch)

Stephen

Fabrico · Oct 18, 2006

ATF works. People have been using it in dirt bikes since the 70's.

I don't recall who makes it, but there is a gizmo on the market the goes on the clutch cable that reduces pull effort (and the throw). There are also some hydraulic clutch conversions.

Converting to a Hinson basket sure helped on my CR500.

Cr250r · Oct 18, 2006

When I was at the Mc show I had a look at the new 06 bikes and the clutch was a one finger pull. I could pull it in easy with one finger ( I assume it had clutch springs fitted !)

My bike is a 91 Cr with Highly modded everything ! I have been trying to find out the difference between the 06 clutch and mine , and I cant see any ( yet ) have ordered 06 clutch springs to see if they are a different rate

Wonder why the hindson basket helped .....

Stephen

Sorry to steer slihtly from the topic of dry clutch

blownharley · Oct 18, 2006

I have a dry clutch on my Harley dragbike. It works quite well but I dont use it that long period ;-)

Fabrico · Oct 19, 2006

The Hinson basket helped overall operation a lot, and pull effort a little. Mainly because it is not only hard anodized but has a greater area in contact with the drive plates. The stock basket is fairly thin and just bare aluminum. The drive plates wear into the stock basket in no time. I imagne it's a whole lot worse on the 500. I think Barnett may have a basket out also.

Below is a picture of the Easy-Pull in-cable unit, about $40.

drwebb · Oct 20, 2006

Dry clutches can be noisier, making them less 'refined' than wet (witness the characteristic Ducati 'clutch rattle'), and they don't handle feathered slipping as well since they are not fluid cooled and so are not common on modern MX bikes that can still glaze the clutch despite the oil. An advantage for road competition is that they don't require an oil drain to make trackside adjustments.

Clutches and brakes (both wet and dry) share a lot of technology. Wet brakes are used on tractors where they control the distribution of power from side to side by continuously slipping. Tractors don't operate at speed, so slipping a dry brake would quickly lead to overheating.

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