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Why does my clutch slip?

Discussion in 'Norton Commando Motorcycles (Classic)' started by Staytite, Jun 10, 2019.

  1. Staytite

    Staytite

    Joined:
    Oct 15, 2011
    Hi all
    For the past 40 years I have taken my clutch apart at the begining of each season and deglazzed and cleaned the plates with solvent. The clutch does not slip till October:)

    I have standard bronze sintered and steel plates and a chain drive. I have always used 200cc of Castrol TQF and there has never been any sign of discolouration due to gearbox oil seeping into the primary chain case.

    Last year I treated my bike to some new bronze plates as the originals (1974) seemed a bit thinner than the specification. The new plates were a shock; all rough and emery paper like. I do not remember them being like that in 1978!

    As the clutch started slipping last week I took it apart. The new rough bronze plates had roughened the once super smooth steel plates. Again, I have not seen this in the past; steel plates have always been super smooth.

    I cleaned the plates with solvent and put it all back together and filled it with 200 cc of Comma AQF which is said to be an equivalent to Castrol TQF.

    But it started slipping within 10 miles:mad::mad::mad::mad:

    So:

    Has anybody esle seen roughing of the steel plates by the new style bronze plates and is it a good thing?

    And has anybody else found that Comma AQF causes clutch slipping?

    Thanks
     
  2. ashman

    ashman

    Joined:
    Jul 11, 2010
    What was wrong with your orginal plates that you replaced them and if the new plates are thinner then that would be one reasons they are slipping as they will have more slack, I am still running my orginal plates after 44 years and all I do is normal maintenance on them, they don't slip using ATF F, my Norton was a everyday ride for most of its life.

    Ashley
     
    Craig and MexicoMike like this.
  3. Staytite

    Staytite

    Joined:
    Oct 15, 2011
    Hi Ashman
    The old bronze plates were thinner than specification and thinner than the new ones. I had presumed the new ones being thicker and rougher would be better! I still have the old ones and will likely put them back in tomorrow for another 40 years
     
    Last edited: Jun 11, 2019
  4. bill

    bill

    Joined:
    Jun 1, 2003
    this is wrong. the thinner plates will lower the stack up and the diaphram spring will have MORE apply pressure along with a harder pull at the clutch lever.

     
    ludwig and Peter R like this.
  5. ELLIS

    ELLIS

    Joined:
    Jan 6, 2017
    Hi Staytite

    I fitted new bronze clutch plates and new steel plain plates on my full rebuild mk3. Bought the plates from Andover Norton and ran the bike for 200 miles. I decided to pull the clutch to check all was well but as you found the plain plates were very scored due to the rough bronze plates. Spoke to Andover Norton about this and they suggested i rub the bronze plates down with 400 grit wet and dry paper to smooth them off which i did. Fitted new steel plates and built the clutch back up. I have only don about 500 miles since and the clutch is performing well. I will leave them in until winter time and then check the condition of them. Sorry i can not give you the answer you are looking for now but will post my findings on strip down.

    Cheers ELLIS
     
  6. ashman

    ashman

    Joined:
    Jul 11, 2010
    Not if the pressure plate has lost its spring tension, in 44 years the only things I have replaced in my original clutch is the pressure plate and centre hub, not bad for 44 years of hard riding.
    My clutch has always been light and can pull the lever with one finger if I wanted to, the only times its ever slipped was running to heavy oil in the primary, took me a long time to work out which oil was the best to use in the first few years.

    Ashley
     
  7. Staytite

    Staytite

    Joined:
    Oct 15, 2011
    Thank you for your replies. While I take note of Bill’s reply the stack height is now what it should as standard as the plates are now as standard. I was thinking of replacing the pressure plate as per Ashley as it’s old and may have lost a bit of it’s “spring” with age (like me!) . I was also considering rubbing the plates to increase their contact surface area, or refitting the old smooth bronze plates for the same reason. Very interesting that Ellis had the same problem with new parts. Did you have a new spring?
     
  8. Peter R

    Peter R

    Joined:
    Dec 13, 2010
    You could also opt for a set of Barnett cluch plates, also much lighter than the heavy bronze plates. This said, the bronze clutch plates almost last forever.
     
  9. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    Or Surflex.
     
  10. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Lots of folk say this about the bronze plates. It amuses me a little though. What’s more important in a clutch, plates that last forever or plates that grip?!

    Is it really the end of the world to change the friction plates once in a while?
     
    Nater_Potater and 998cc like this.
  11. Peter R

    Peter R

    Joined:
    Dec 13, 2010
    What's the point in replacing clutch plates while they still have sufficient grip ? In my experience the bronze plates last a long time, without noticeable wear or loss of grip. If the stack height decreases due to wear, the force required to operate the clutch will increase, that would be a reason for replacement imo.
    Apparently, according to the posts here, there seem to be a problem with the specifications of the broze plates that are supplied lately.
     
    dynodave likes this.
  12. kommando

    kommando

    Joined:
    May 7, 2005
    If you roll sintered bronze with a 5% reduction you get a smooth surface, you need to start with a 5% thicker material of course. The RGM ones with the narrow band of bronze look to be rolled.
     
  13. ashman

    ashman

    Joined:
    Jul 11, 2010
    Like I have said my orginal plates have been in my bike for 44 years now, first few years had some slippage from using motor oil which was in the bible but finding the right oil to run fixed that problem my Norton has over 160k mile and most of its life a everyday ride, convered it to the Featherbed back in the early 80s with a hot motor, and in my younger days it copped a hiding, from burn outs to doing long wheelies, and to this day still the same plates, it don't slip at all, have never done the stack height, the only time I touch the clutch adjuster is when doing maintenance, I ran them dry when running a belt drive, but gone back to chain, my lever has always been light, so in my opinion why change when its been working great for me.
    Sometimes I wonder why so many have troubles with the bronze plates, but then I do call my Norton the freak.

    Ashley
     
  14. ludwig

    ludwig

    Joined:
    Aug 30, 2006
    Bronze plates may last forever, but they do ruin the clutch centres, even the 'hardened' ones .
    You only changed one centre in 160k miles ?
    Amazing..
     
  15. bill

    bill

    Joined:
    Jun 1, 2003
    just where did you come up with this. the pressure plate is a just that ,it has NO spring quality about it and it would break if it was flexed.this and the last comment just shows your lack of knowledge about the clutch.

     
  16. concours

    concours VIP MEMBER

    Joined:
    Dec 29, 2011
    The rough surface finish you describe on the bronze plates = less contact area = less torque capacity of the clutch. Those parts are shite, and have ruined your steel plates. I didn’t see who provided them, but they should go back, “not fit for purpose”.
    Get new steels & Barnet’s, be done with it.
     
    B+Bogus and Nater_Potater like this.
  17. ashman

    ashman

    Joined:
    Jul 11, 2010
    Yer its a freak my Norton amazes me as well and my mate who got me into Nortons and Featherbed frames can't believe it, he went the other way building Tritons, in his own words Triumphs are more reliable lol, he eats his own words everytime he comes around.
    Yes they do eat the clutch centres and I only replaced the orginal one 7 years ago, not sure how long the one I replaced with will last, mine you it was pretty flogged out when I replaced it.

    Ashley
     
  18. jbruney

    jbruney

    Joined:
    Jan 5, 2019
    My Mk II at 20k still has all the original clutch. It used to suffer from slip until I actually learn to adjust it properly, and it now seldom requires attention. I don't really thrash it these days, but rather permit the bike to breath well regularly in a vigorous manner lest it begin that infernal intermittent sputter.
     
  19. jsnorton

    jsnorton

    Joined:
    Oct 10, 2018
    I installed a Barnett clutch in 1985, still going strong to this day.
     
  20. rvich

    rvich VIP MEMBER

    Joined:
    Jul 25, 2009
    I love clutch threads. First, people often confuse the "pressure plate" with the diaphragm. I think we have to accept that even speaking the same language, that we don't. The oil you put in the primary should not be soaking the plates down in the first few miles. If it does then I would think the primary is over-filled. If that is the case then the type of oil may have a significant impact on clutch grip but otherwise no. Unless the stack height is so low that the diaphragm can't place adequate pressure on the stack then I would suspect there is something wrong with the adjustment or assembly. Is the center notched from running bronze plates? Is it possible the plates can't make contact because they are trapped in the notches?
     

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