Dry Clutch / Wet Clutch?

[manxie]

This is probably a silly question but.....I`ll ask anyway?

I`m far from a mechanic and I think I know the difference between a wet clutch and a dry one but how can you tell what it fitted to your bike? I`m guessing my MZ and GB both have wet clutches but to be perfectly honest....I don`t know? How can I tell?  You hear things like Ducati`s rattling like buggery which is the dry clutch?

 

[themoudie]

Aye Steve,

MZ and GB wet clutches running in engine/gearbox oil of unit construction engine.

Ducati singles usually the same, but for racing purposes, by using a new clutch cover casting and oil seals a dry clutch can be run. Advantages of a dry clutch are less slip and better grip, no loss of power due to the drag of the oil on the clutch assembly as it tries to spin through the oil!

There are the two types of clutch plates; they are steel drive plates (take the power into the gearbox via the inner clutch hub) and either fibre or sintered metal plates that take the drive from the crankshaft via the outer clutch basket. Again road going dry clutches generally use fibre plates bonded to steel or aluminium alloy cores, whilst race clutches often use the sintered plates as these are less likely to slip especially when hot.

The steel/ sintered plate clutch behaves as a 'power switch' and can be grabby in its action. Also after a few races its best to wash the clutch plates in brake cleaner, so as to maintain the grip of the plates on each other, any oil or debris from the track effects the grip of the plates. Also good quality springs within their length tolerance are also required to maintain that pressure.

The rattling Duke clutch of the V twins and their open construction means that road dirt and grit can easily get in and act as a grinding paste on all of the clutch parts    , often the chattering clutch is caused by excessive wear between the tabs of the friction plates and the arms of the clutch basket, this chattering and wear also results in ridges forming on the clutch basket arms and this can prevent the clutch from releasing as well as it might.

My apologies for the ramble, essentially if you can afford high maintenance and will utilise the potential minuscule grip and horsepower gains offered, use a dry clutch with steel and sintered metal plates. For road bikes a wet clutch either using oil from the unit construction motor or its own oil bath al la pre unit Brit bikes does an admirable job and saves an awful lot of wear, maintenance and expense.

Chap on!

My regards, Bill

[manxie]

Hey Bill,

thank you for your explanation, very informative 

The reason I`d asked was I went to get oil for the MZ yesterday and I saw a 4 stroke motorcycle oil, 10 / 40 semi synthetic "suitable for wet clutches" and thought ... "oh, is that what I need?"

My mate has a K series BMW and he was recommended not to use a semi synthetic oil as over time it could cause his starter clutch to slip (I know that`s a different thing) Gone are the days when anything can be lashed in then? 

Thanks again Bill,

Steve 

[guest1247]

Good morning Steve, Bill's words are about as "spot on" as you can get... I would like to add something that would be regarded as "general knowledge" by most that read these pages... For modern unit construction engines, ie, engines and g/boxes running in the same oil, semi-synthetic is fine... ( it is all in the handbook ), However... FULLY synthetic oil has additives that will bond to internal areas, particularly friction areas, that will do exactly as stated on the tin ... that is , make them slippery ..!!  Not what you need from your clutch linings ... The only time I would deviate from the manufacturers recommendations in the handbook, is to change any oil sooner than they recommend ... An old saying, "At the end of the day ... oil's cheap" ... Regards, Tony

[Moto63]

 Morning Bill, yes very informative post.. I, probably like most on here knew the "basic" differences but as Tim once said "everyday is a school day" and you definitely gave me a very interesting lesson in your post. Oh and I like the bit in your other post where the house is a tad pongy cos you're baking the hammerite paint in the oven...classic stuff.
Cheers, Michael

[SteveC#222]

BMW's ( and for that matter Cossacks, Ural's and Dnieprs) are slightly different in that due to the engine / gearbox layout they use essentially a Car type clutch with 2 great big plates. This works well without a lot of the problems and maintenance of the Ducati set up.  Although it wasn't unknown on the Ural for the clutch screws to come loose and try and eat their way into the gearbox!!

[themoudie]

Good afternoon All,

Thank you for your compliments on my initial reply.

Two further points:

As you point out Steve (Manxie), there are semi-synthetic 10W-40W oils that have additional additives that can contaminate wet plate clutches and those where these additives have been omitted or are of a different formulation so that wet plate clutches are not affected. I am not a petroleum chemist, so cannot explain how the latter might be achieved!  I used to stick car 10W-40W in both Sally (SRX600), Herman (MZ660 Tour) and the Bros (Honda400 'V' twin), all eventually suffered from slipping clutches when "wound on" in 3rd to 5th for overtaking manouvres etc. Now using Morris motorcycle 10W-40W for all bikes, Sally (SRX600), Morini the Minx (Morini 125H) and the Bros (Honda400 'V' twin), with no slippage from the clutch. In previous debates on this forum others have not had problems with using car blend 10W-40W oil in conjunction with wet plate clutches and I offer no explanation for this. 

Thank you SteveC#222 for lobbing the car type clutch into the debate and as these are usualy dry clutches (fibre plate bearing on the steel flywheel) and protected by an aluminium bell housing casting at the back of the motor between the crankcases and the gearbox cases; I hadn't thought to mention them! 

My regards, Bill

[manxie]

Great info in your replies fella`s, thank you.

So would a 10 / 40 mineral oil be the best to use? Or a semi synthetic?

[themoudie]

Hey Bill,

thank you for your explanation, very informative 

The reason I`d asked was I went to get oil for the MZ yesterday and I saw a 4 stroke motorcycle oil, 10 / 40 semi synthetic "suitable for wet clutches" and thought ... "oh, is that what I need?"

Thanks again Bill,

Steve 

Aye Steve,

Answered your own question as above. Check out Fleabay, but I understand carriage may be an issue or otherwise go and speak nicely to 'Road and Track' in Douglas, they know what they are about and give good advice.

Link: Road and Track, Douglas

However, this appears to be a good deal on Fleabay and Motul is a quality brand: Fleabay_Motul_oil_20litres

I got Morris 25 litre drum for less than this (£99-00), but the seller on Ebay dosen't despatch to IoM! 

Regards, Bill

[iansoady]

However... FULLY synthetic oil has additives that will bond to internal areas, particularly friction areas, that will do exactly as stated on the tin ... that is , make them slippery ..!!  Not what you need from your clutch linings ... ... Regards, Tony

That's not quite true. It's only oils that have friction modifiers (used principally to improve mpg) that are a problem. Fully synthetic bike oils are fine. So are many car oils but you do need to be careful.

I used full synthetic in my Triumph Tiger with a wet clutch for 20,000 miles with no problems. But I think the SLR650 is fine on semi.

[Richard]

And when it comes to older machines like airhead BMWs also consider the ZDDP content of the oil.

Old Beemer owners argue about oil nearly as much as two stroke MZ owners do.

[johnr]

Old Beemer owners argue about oil nearly as much as two stroke MZ owners do.

just to clarify, are you talking about owners of older bmw's, or are you talking about older owners of bmw's

[Richard]

Generally one and the same thing.