Barnett clutch friction plates

1up3down said:

My commandos have always had wet clutches.

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um no, Commando clutches are dry, they require no lubrication to operate

however, they live inside an enclosed primary that has oil to lube the chain and it is that oil that finds its way onto clutch plates inside of the basket

in addition, some gear can can, although not designed to, find its way along the rod and into the clutch area

and it is that oil sources that contaminate the Commando dry clutch and often cause the plates to slip under load, requiring period cleaning and removal of that oil

many Commando owners converted to belt primaries, myself included, and one great benefit is that the clutch remains dry with no chain oil in the primary
and the result is a no leak primary along with no need to ever remove and clean the clutch plates of oil

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If the clutch lives inside a wet compartment, without seals separating it, how do you manage to describe it as a dry clutch?

The 850 Commando clutch with Barnett Kevlar plates presoaked in ATF, then run with ATF in the primary, works perfectly.This has been a run it and forget about it clutch for me. With the stack height set properly, a Dyno Dave seal on the pushrod and a slippery Venhills cable, it can be operated with one finger, engages smoothly and doesn't slip on stock power.

Glen

I wonder what year Norton started putting oil in their primary cases. From that time onwards, the manufacturers would have been having to design "wet clutch " linings.

Should start a quiz here. How many manufactures used "wet" clutches in their transmissions. I'll hazard a guess for a start. All auto transmissions with clutches.

Dereck

Lets get so info out to the uneducated. All Norton's had wet clutches in their oil bath transmissions until the post Norton period when the belt drive system was implemented.

Fast Eddie wrote: "If the clutch lives inside a wet compartment, without seals separating it, how do you manage to describe it as a dry clutch?"

The designers either assumed the clutch would run dry, or were mis-led .... thus the design is a dry clutch.
Norton put it in a wet bath and ran it as a wet clutch. I suppose one could say, it was a case of the dry hand not knowing what the wet was doing.

BTW ... somewhere I remember reading that Ford Type F ATF produces 35% more friction than oil. As worntorn writes above, this difference can be sufficient to eliminate slip.

Slick

A clutch lesson for those unaware. YET AGAIN x 10 to the power n.
750 Commando.
THE REQUIRED CLUTCH TORQUE CAPACITY. Max crank torque 48 ft lb. Primary ratio 26-57. Assuming incorrectly no power loss in chain max torque at clutch = 48 ft lb x 57/26 = 105 ft lb. A rule of thumb safety / service factor given in one ref book in my local library is to use x2. Thus the REQUIRED torque capacity of the clutch is 105 ft lb x 2 = 210 ft lb. The Chief clutch Designer and Engineering Director whose brain I have picked at for decades on clutch and diaphragm spring design employed, rule of thumb x1.6 for multi cyclinder car clutches and x2.4 for lorry/bulldozer/tractor etc clutches so for our single and twin cylinder lumps x2 seems a reasonable safety factor to employ. It is probably a bit OTT but better to have a slutch that does NOT suffer slip problems than one that doesMany years ago I was told that the new Triumph Japanese designed clutches employed a safety factor of x 1.4 but Japanese clutches have been describes as being MINIMAL in torque capacity which is probably why Barnett flog so many stronger clutch spring kits????
THE IN THEORY CLUTCH TORQUE CAPACITY. The clutch employs 4 friction plates = 8 friction interfaces. The effective radius of the friction inyerfaces is approx 0.205 ft for the original friction plates. The clamp load applied to the friction interfaces given by THE ORIGINAL 0.075 inch thick diaphragm spring was, according to Nortons own test results and the results of the testing I had conducted by a certain Engineering Univerity approx 380 lbf. The Friction material employed according to the Norton drawings was Ferodo MS6 of which the data sheet gives C of F values for design purposes of DRY 0.34. OIL MIST 0.1-0.12. OIL 0.09. Thus the in theory torque capacity of the clutch is...
DRY 8 x 0 205 x 380 x 0.34 = 212 ft lb.
OIL MIST 8 x 0.205 x 380 x 0.12 = 75 ft lb.
IN OIL 8 x 0.205 x 380 x 0.09 = 56 ft lb.
Thus I would SUGGEST that the original 750 Commando clutch was a WELL designed TORQUE CAPACITY WISE dry clutch and that the problems of slip and drag it suffers are due to the oil in the chain case enering it.
Now I note many report no slip problems but Norton had a slip problems and the heat generated by the slipping fully engaged clutch resulkted in a BIG heat build up in the clutch which damaged the adhesive bond sticking the postage stamp lumps of friction material to the steel backing plate which then resulted in them jamming up the clutch and the clutch not freeing off correctly (AS IS STATED IN THE NORTON OWNERS CLUB COMMANDO SERVICE NOTES) To overcome this and TO TRY TO CURE (and fail) the slip problem Norton made two changes. They changed the clutch plates to solid asbestos based DON 112 friction material for which its data sheet only gives a DRY C of F value of 0.34 at 100-200C rising to 0.4 at 400C. It gives NO oil mist or in oil values. They also had Laycock Engineering manufacture thicker diaphragm springs which increased the clamp load given by the spring. IN FACT they did this trick several times and the clamp load rose from 380 lbf to approx 550lbf for the last version (0.084 inch thick) used on later 750 and 820 clutches which of course resulted in heavier clutch lever action.....
As you should ALL now be aqble to calculate even using the C of Fof 0.15 - 0.17 given for the wet use Barnett friction materials even with a 550 lbf clamp load the clutch still has no where near enough torque capacity. The LAST DITCH attempt to cure the slip problem was to BODGE IT as was done by VILLIERS years previously on their STARMAKER diaphragm spring clutches which had a serious slip problem but when you fail to tell the clutch designer it is going to run in oil he is going to design a DRY clutch.....as his original design notes show!!....They changed to sintered bronze friction material so that when slip occured due to oil the slip generated high temperatures within the friction interfaces which in theory burnt off the oil leaving the clutch once again in theory DRY. Of course the burnt off oil in Commando clutches ends up as a, being polite, black bunge that results in drag problems and its back to washing the plates in petrol yet again.... Rule of thumb C of Fs for sintered bronze are DRY 0.3 and WITH OIL 0.06-0.08 and the Gentleman I have consulted for decades employed 0.06 for ALL his MANY wet bronze plated car and lorry etc clutches made for the UK , USA and European vehical manufacturers over a great many years and he refered to 0.08 as being a bit optimistic.
For those wanting to do a bronze plated 820 clutch calculation max crank torque is 55 ft lb, there are 10 friction interfaces and the effective radius is approx 0.21 ft. Oh sod it
55 x 57/26 =120 ft lb x 2 =240 ft lb.
Dry.........10 x 0.21 x 550 x 0.3 = 346 ft lb.
OIL........10 x 0.21 x 550 x 0.6 = 69 ft lb.

Now what if the 820 clutch designer was UNAWARE that Norton had changed the diaphragm spring and employed the 380 lbf of the original spring?????/
DRY........10 x 0.21 x 380 x 0.3 = 233 ft lb...
Gosh a well designed TORQUE CAPACITY WISE dry clutch giving a clutch lever EASILY operated ALL day long with two fingers. Mind you the bloody flywheel should be on the crank and NOT the gearbox main shaft but clutch rotating weight is another subject............

J. M. Leadbeater said:

OIL........10 x 0.21 x 550 x 0.6 = 69 ft lb.

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0.06

texasSlick said:

Fast Eddie wrote: "If the clutch lives inside a wet compartment, without seals separating it, how do you manage to describe it as a dry clutch?"

The designers either assumed the clutch would run dry, or were mis-led .... thus the design is a dry clutch.
Norton put it in a wet bath and ran it as a wet clutch. I suppose one could say, it was a case of the dry hand not knowing what the wet was doing.

BTW ... somewhere I remember reading that Ford Type F ATF produces 35% more friction than oil. As worntorn writes above, this difference can be sufficient to eliminate slip.

Slick

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On what basis do we assume the designers were so incompetent? How do we know they did not design the clutch as a wet clutch? It is not exactly strange, many motorcycle clutches were wet then... and it is quite normal today too...

Fast Eddie said:

On what basis do we assume the designers were so incompetent? How do we know they did not design the clutch as a wet clutch? It is not exactly strange, many motorcycle clutches were wet then... and it is quite normal today too...

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On the basis that it slips.

texasSlick said:

Fast Eddie wrote: "If the clutch lives inside a wet compartment, without seals separating it, how do you manage to describe it as a dry clutch?"

The designers either assumed the clutch would run dry, or were mis-led .... thus the design is a dry clutch.
Norton put it in a wet bath and ran it as a wet clutch. I suppose one could say, it was a case of the dry hand not knowing what the wet was doing.

BTW ... somewhere I remember reading that Ford Type F ATF produces 35% more friction than oil. As worntorn writes above, this difference can be sufficient to eliminate slip.

Slick

Click to expand...

That was not my experience, with the stock bronze plates and Type F ATF my clutch would start slipping on about a yearly basis and I could temporarily fix this by cleaning the plates, have been using Barnett plates and Type F for a few years now and the clutch works great with no maintenance required...FWIW soaked the Barnett plates in ATF before installation.

Triton Thrasher said:

Fast Eddie said:

On what basis do we assume the designers were so incompetent? How do we know they did not design the clutch as a wet clutch? It is not exactly strange, many motorcycle clutches were wet then... and it is quite normal today too...

Click to expand...

On the basis that it slips.

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That's kinda fair, but its only an assumption...

If that is the case, it clearly demonstrates that the clutch is not exactly the best design, but it is not evidence that the ckutch was designed to be dry and was then run wet. That is an assumption which may or may not be correct, but its not proof.

Its also not taking into account that many owners have clutches that do not slip!

I'm not defending the clutch per se (my own clutch is modified with Barnet plates and runs dry), I am simply saying that there doesn't appear to be any conclusive evidence showing such a simple solution as the clutch was designed as a dry and then run as a wet clutch.

Fast Eddie said:

Triton Thrasher said:

Fast Eddie said:

On what basis do we assume the designers were so incompetent? How do we know they did not design the clutch as a wet clutch? It is not exactly strange, many motorcycle clutches were wet then... and it is quite normal today too...

Click to expand...

On the basis that it slips.

Click to expand...

That's kinda fair, but its only an assumption...

If that is the case, it clearly demonstrates that the clutch is not exactly the best design, but it is not evidence that the ckutch was designed to be dry and was then run wet. That is an assumption which may or may not be correct, but its not proof.

Its also not taking into account that many owners have clutches that do not slip!

I'm not defending the clutch per se (my own clutch is modified with Barnet plates and runs dry), I am simply saying that there doesn't appear to be any conclusive evidence showing such a simple solution as the clutch was designed as a dry and then run as a wet clutch.

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Yes and it probably doesn't matter much. The clutch either works, which we like, or gives problems, which we try to fix.

Fully submerged.... and that's Dexron, not Type F. :mrgreen:



Level lines

Ok. what year did British motorcycles start using the oil bath primary.

Once we know that, then we can the tell how stupid the clutch designers were to believe all the bike designers were lying to them about their clutches being dry clutches.

How stupid all the British bike makers must have been. [ not just Norton ]

Its realty a wonder they survived after the 20"s.


No wonder the Japs took over. They could do it with their eyes closes and their hands tied behind there backs.

Let face it, Daimler had pre-selector gearboxes with bands that grip drums to select the gears. Those bands had linings in them, and the gear boxes were filled with oil. [ I could be mistaken of course. ]

Of course. Taking the piss again.

Dereck

kerinorton said:

Ok. what year did British motorcycles start using the oil bath primary.

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As for the whole British motorcycle industry, I don't know the history of primary drives and clutches. However, according to Norton Twin Restorations by Roy Bacon, "Early clutches also had a band round the drum to keep oil off the plates, but with the AMC gearbox came new clutch inserts from Klinger that could cope with the oil so the band was no longer fitted." I believe that 1956 was the year that this change happened. Unfortunately his book does not have any pictures of clutch assemblies so I don't know what these bands look like. Seeing that the Commando clutch assembly is not submerged in oil maybe the clutch should be considered semi-wet or semi-dry. :wink:

Peter Joe