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Weak links

Discussion in 'Norton Commando Motorcycles (Classic)' started by Fast Eddie, Apr 15, 2018.

  1. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    Out of curiosity, what are the main known weak links on a Commando? Here’s the ones I know of, please adivise if different:

    Starting from the head and working down and back...

    Head: RH4s know to crack. All others OK?

    Rockers and valve gear OK?

    Pistons: Slotted 750 type known to break. All others OK?

    Rods: have been known to break, but generally considered OK.

    Cam: Some later cams found to be soft and prone to wear.

    Crank: Flywheel known to break up. PTO shaft known to break where it meets the cheek.

    Crank cases: Known to break under racing conditions and occasionally on the road. Combat issues with main bearings and oil return ?

    Primary: Bronze clutch pack puts heavy weight on main shaft. Otherwise OK?

    Gearbox: Case known to crack between bearings, mainshaft known to flex (causing the aforementioned?). Layshaft bearing weak on later models. Otherwise OK?

    Rear wheel: Two piece wheel spindle known to break.

    Please let me know if I’ve missed, or miss represented any know weak points.
  2. JimC


    Oct 12, 2007

    Wet sumping? Judging by the machinations of some, it must qualify.
  3. kommando


    May 7, 2005
  4. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
  5. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    Strewth, you’re persistent aren’t you ?!
  6. JimC


    Oct 12, 2007
    In 1969, no one in his right mind would have chosen a Commando over a Honda CB 750. I will admit, I was not of right mind in 1969. Nortons have the allure of a beautiful, narcisstic woman. Great to look at, but extremely troublesome.
    Nater_Potater and Welshrugby like this.
  7. JimC


    Oct 12, 2007

    Sometimes the hole you dig to trap another being ends trapping yourself. As the engineer hoisted by his own petard, so to speak.

    As they say in the south (U.S.), bless your heart.
  8. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    Quite right sir.
  9. auldblue

    auldblue VIP MEMBER

    Nov 20, 2012
    More like fausted by ones own p'eter, If it's a wet sumping thread! Not quite an idiom but give it a few hundred years and you never know ,it may well be. Probably by then wet sumping will be a thing of the past also ,never to be discussed again except by individuals with a wet towel wrapped around their heads talkin about the good old days and watching black and white PG tips adverts on utube, More tea vicar!
  10. ashman


    Jul 11, 2010
    Well when I was 17 years old buying my first road bike in 76 all my mates were into CB 750 4s but I didn't like the top heavyness of the Honda's and my mate gave me a ride of his hot 750 Commando in a Featherbed frame for the day while he rode my Honda dirt bike, well that was me I been hooked ever since and brought my new 74 Commando 2 weeks later well none of my friends have theire old Honda 4s now but I still own my Norton which I converted to a Featherbed in 82.

    As for wet sumping not all Nortons do it mine has never done it in 42 years but then I ride it regularly, but maybe it will now that its sat for just on 12 months while doing other things to it and riding my Thruxtons.

  11. JimC


    Oct 12, 2007

    I beg to differ with your definition. Here’s the definition I found:

    Shakespeare in "Hamlet", used the phrase "hoisted on his own petard" to describe someone caught in his own trap. ... To be "hoist by one's own petard" is to have your plot against someone backfire on yourself.
  12. Mr. Rick

    Mr. Rick VIP MEMBER

    Feb 6, 2009
    Not sure who is plotting, or whose heart is being blessed, and this is sorta uncomfortable, like calling out your friend's faults, but to the original post, we might add:

    Fractured oil tank bottom fittings
    Chain oilers that "over-performed"
    Mediocre non-serviceable rear shocks
    Oddly designed front forks
    Marginal charging system
    Dim headlamp
    Poorly plated spokes
    Weak front brakes
    Swingarm spindle problems
    Carelessly placed timing marks
    Air filter that scraped off frame paint with every service attempt
    And how cd I have almost forgotten the bloody speedo drive!

    I love my bike, and I'm pleased to address most of these "issues".
    Last edited: Apr 15, 2018
  13. Fast Eddie

    Fast Eddie VIP MEMBER

    Oct 4, 2013
    Hmmm, that’s quite a long list of extra, and valid, points Mr Rick!
  14. hobot


    Oct 19, 2005
    Add faulty functional forks to the fragile Commando fruit cake. Its a crazy making illogical cheap stop gap short cut contraption that appeals to hobot, which should give pause to others on their sense of judgment. At least Lucas smoke system is reliable, especially the bullets. oh yeah - Horn deserves honorable mention to me. Nortons were accidental/opportunist acquisitions to me, not sought out, so I deserve my ignorant fates, but rest of yo'all are the real nutz cases to volunteer for it.
  15. SteveBorland


    Nov 15, 2010
    Gears tend to pit on the tooth faces
    just about every bloody nut, bolt or stud is designed to be as inaccessible as possible...
  16. oldmikew


    Jul 25, 2015
    But is wet sumping a bad thing ? It means that on start up plenty of oil gets throwen up the bores and over the cam ?
  17. Onder


    May 11, 2010
    There is no logical reason to own any older brit bike at all. Well perhaps a few exotics as investments. Otherwise as idiotic
    as running a 1920 gravity coal boiler in your basement.
    And just for the record, I own four. Pathetic .
    o0norton0o and Nater_Potater like this.
  18. baz

    baz VIP MEMBER

    May 26, 2010
    Blimey four boilers !!! Must be cold out your way!!!
    delagem, MFB and MikeG like this.
  19. 84ok


    Aug 10, 2014
    dunno about weaker but frame neck angle change for 850, yokes not compatible wth prior,
    early frames 'widowmakers' & stll see them, but most are fixed,
    rear frame loop weak, bends

    early sidestands changed modified,
    center stand itself upgraded (stronger) visually different, also went from frame to cradle mount,
    - my 74 original still broke (weld) tho

    3 type swingarm welded cross member supports near the pivot end i'm aware of,
    early is tubular, then beefed up twice for 850,
    next is rectangular with a pronounced v shape facing aft,
    final 75 on, rectangular

    early no cush, later wheel cush problematic, new for 75 way better but not an easy fix for prior

    original left footbrake lever if the cable breaks,
    original front brake master cylinder bore/piston size

    primary cover oil seal, running oil also results in clutch slippage,
    gearbox cover seals (o-rings mod fix),

    proper oil filter introduced at some point

    cylinder head exhaust pipe threads strip

    afaik ^
    Last edited: Apr 16, 2018
  20. Danno


    Feb 7, 2010
    The weakest point is the design of the crank and cases. Two outboard main bearings with all that flexible mass spinning in between is a recipe for disaster. I would not attempt to really power one up without uprated cases and crank. Then there's the non-unit construction......

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