NATIONAL BRAKE & CLUTCH, CORK INSERTS GIVE RESULTS

On a typical Brit bike "clutch that gets oily," cork faced plates do give good results. That's what's in my bike now.

Here's part of the arrangement:
NATIONAL BRAKE & CLUTCH, CORK INSERTS GIVE RESULTS
 
I had a Villiers powered beastie where the engine could get ahead of the cork clutch plates.
I just can't imagine discarding Ferodo inserts and replacing with cork.
Most brit factories went Ferodo inserts in the 1930s.

In 1910 though, cork was probably a big improvement on metal-to-metal....
 
Rohan said:
I had a Villiers powered beastie where the engine could get ahead of the cork clutch plates.
I just can't imagine discarding Ferodo inserts and replacing with cork.
Most brit factories went Ferodo inserts in the 1930s.

I
...
Click to expand...

Your Villiers may have been much more powerful than my 650, for all I know.

You don't have to imagine it. I'm not the only person who has picked the inserts (in my case Surflex) off the plates and stuck cork in its place and cured clutch slip.
 
Norton clutches have an oil excluding ring around them.

I had always kinda assumed it was to keep oil out of them...
 
Rohan said:
Norton clutches have an oil excluding ring around them.

I had always kinda assumed it was to keep oil out of them...
Click to expand...

It may have been for that, but did it keep the oil out?

And does my blurry pic up there look like a Norton clutch?
 
The parallel thread to this - that prompted this thread - was asking about a Norton clutch.
The blurb does say they were designed as a dry clutch.
Quite why we have gone back to 1910 defeats me a little.... !
 
Shame people are clearly incapable of using Google.......
Cork was employed since the beginning of time as a friction material because of its HIGH Coefficient of Friction both DRY and WET (with oil). Mr Hopwood once told me that he employed a C of F of 0.3 for all his wet cork clutch calculations.
Reference books in my local library list its C of Fs as DRY from 0.5 to 1.0 and WET from 0.3 to 0.5. Thus its WET C of F is GREATER than that of the Ferodo MS6 material that was employed on the original Commando friction plates (C of Fs for design purposes being listed as DRY 0.34. OIL MIST 0.1 - 0.12 . IN OIL 0.09.) Even the later employed solid fibre asbestos based DON 112 material plates only had DRY C of Fs listed and are shown on the data sheet as 0.34 at 100-200C rising to 0.4 at 400C. NO wet values are given. Thus Triumph in employing cork ended up with wet clutches of roughly the same torque capacity a dry clutch and with the same number of friction plates etc. mind you go read the book on the development history of the Bonny and read about the notes going from the development dept stating that the new T110 clutch had a torque capacity of 83 ft lb and the motor could shove 80 ft lb through it...most designers employ a safety factor and a rule of thumb one is to use X 2!! I.E. they were in deep doggy doo clutch torque capacity wise.
UNFORTUNATELY as every Triumph owner of my era will be FULLY aware there were problems with cork especially when the clutches were being used by youngsters playing at boy racer defying death and injusy and often failing (as I remind people stating that one section of the old A20 near Brands Hatch was named DEATH HILL) when the clutch heats up the cork swells causing god awful drag problems and it sticks like the proverbial to a blanket to the steel interplates requiring the clutch to be freed off BEFORE starting the motor and in my experience sometimes requiring the clutch to be taken apart to free it off and NOT just wirth Triumph so called clutches!!!. It was so bad Triumph stated in the manuals that the clutch should be freed off FIRST before starting the moto!! See the Triumph Workshop Instruction Manual 1945 - 1955 Speed Twin ...Tiger 100... Thunderbird etc Page 20...'Lift the clutch lever and depreess the kickstarter two or three times to seperate the clutch plates'. A Motor Cycle Sport Triumph twin road test once reported 'As with the last Triumph tested it was possible to start the motor with the clutch lever back to the bar'. at the time I though..'Bloody hell an honest road test'. A Triumph Service Manager once told me that workers upon dismounting would park their bikes leaning against brick walls with the clutch lever pushed back to the bar and give the kickstarter a few jabs to ensure the plates were freed off so they would be when they left work later...A BSA gentleman friend told me it was the same at BSA and he told me the younger membersw of staff had a competion to see who could ride their BSa the furthest before their clutch freed off!! He mentioned 14 miles if memory is correct!!!! bob Oswald of QPD in the USa started making belt drive systems for Triumphs in the first place because as a Triumph dealer he became rather fed up with owners trucking their bikes back to him saying in no uncertain terms 'YOU SOLD IT TO ME YOU FREE OFF THE ****** clutch' which apparently he would do FOR FREE in an effort to keep his customers faithful to Triumph.

Many years ago I received some info on a friction material employed on a certain manufacturers Triumph friction plate friction material ...... the hand written translation from the Italian data sheet states the material is...rubber, heat hardening resin, what looks like basult fibre, cork granuals, accelerator and anti aging agents. DRY C of F values given are MINIMUM 0.35 at 30c to 160C. MAXIMUM 0.54 AT 90C. Handwritten C of Fs to be used for design purposes are given as In oil 0.16/0.17 and Dry 0.22/0.25.
The C of F value for 'suitable for dry use only Ferodo MZ41 as employed for Cold Star clutches 1954-1956 has a DRY C of F for design purposes given as 0.41. (Some people think Gold Star clutches were designed as wet clutches because they run within an oil bath chain case!!) Mind you Mr Hopwood did once make the point to me that Gold Stars were a clubmans race bike which would receive regular maintenance after every meetings and any oil entering the clutch would be removed before it caused slip problems. Theory is a wonderful thing!! I had a friend who had to change his slipping Gold Star clutch halfway through a Senior Manx GP and he still finished ..... For his road going 650 BSA twin design Mr Hopwood borrowed an old Rudge idea and fully enclosed the clutch so chain case oil did not enter it.....As Mr Nicholson states in his book Modern Motor cycle Mechanics...'Most problems with this clutch are due to oil working in' and my money would be on that in 99% of cases owner incompetence was responsible.
when Nortonn introduced their pressed steel oil bath CHAIN case to give the primary chain a much better form of lubrication than that provided by mud stones human bone and flesh etc they did NOT design a wet clutch. They had no monet or time to do the job correctly and they bodged it...The clutch was still a DRY clutch...the oiul level plug was set such that oil at the CORRECT level just touched the lower run of the chain creating an oil mist in service(Gold Star filling instructions state 'Till oil can be seen to be just touching the chain')...they shoved an OIL EXCLUDING BAND around the basket and employed a recently developed Ferodo friction material that did not fall apart with oil contamination. I once spoke to Mr Plil Heath who was part of the Norton oil bath chain case development team in the 1930s and he made the comment that with everything correct the clutch would work perfectly for many thousands of miles use but that the low oil level did little for chain life. I laughed my **** off!!... He also stated that the correct grade of oil was a straight engine oil of SAE10 or 20. My A65 workshop manual recommends Castrolite which was a straight 10-30 oil now no longer available in the UK. I believe either Silkolene or Morris oils flog a straight SAe20 oil in quart pots.
Just because o motor5 cycle manufacturer shoved their clutch within an oil bath chain case does not mean rthe clutch was designed to work correctly with oil on the friction interfaces. Even the staff of The Motor Cycle describe the idea of shoving a clutch within an oil bath chain case as and I quiote from Speed and How to Obtain it...'FRANKLY A COMPROMISE' and that is exactly what it was, done to save time and money.
I was trying to think of any race bike which had a wet clutch....and failed. Did you ever see the clutches on Mr Bearts 350 and 500 Manx bikes used in the TT and Manx GP?? I never did understand how the got round with so few plates in the clutches but In those days of youth I knew nothing about clutches and the effects of oil on clutch torque capacity...rather like most Norton owners apparently although most a fully aware of the effects of oil when their tyres hit a patch and if they arent they will be..one day as they follow their bike down the road whilst on their arse!! Funny thing is one smells it first but by then its toooooo late!! In my experience that is.
NO SPELL OR GRAMMER CHECKS DONE..Dinner awaits.
 
Sooooo, F1 cars all use cork clutches then ???

Nope, before anyone says anything silly ...
 
Triumph clutches did stick, though all the ones I messed around on freed off with little trouble.

The cork lined lash-up pictured above doesn't stick; it's also "dry," but some oil gets in from the gearbox and probably from the engine too.

It grips like an Aberdonian on a £5 note.
 
You must log in or register to reply here.
Back
Top