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Deposits on Piston Tops

Discussion in 'Norton Commando Motorcycles (Classic)' started by NickZ, Nov 27, 2019.

  1. NickZ

    NickZ VIP MEMBER

    Joined:
    Oct 31, 2018
    While performing post break-in maintenance after top end work on my 1971 Roadster (cylinders honed, new rings, new valves, head gasket, etc.) I noticed ugly deposits on the tops of the pistons. More pronounced on left side but some on right as well.
    Does anyone have ideas of what would cause this and what to do about it?
    For the last 100 miles I have been running Sunoco 260 GTX Unleaded 98 octane fuel. Carbs are standard Amal concentrics. The bike has been running great. Starts first kick cold & hot, idles smooth at 1000rpm. Good performance through the throttle twist.
    I provide pictures below:

    2 photos of the left piston:

    then 2 of the right piston:
    Then this is what they looked like approximately 100 miles before:
    Then a picture of how the plugs look now:

    Any help is appreciated. IMG_2854.JPG IMG_2855.JPG IMG_2856.JPG IMG_2857.JPG IMG_2688.JPG IMG_2689.JPG IMG_7201.JPG
     
  2. Torontonian

    Torontonian

    Joined:
    Dec 28, 2009
    Why did you pull the head to look ? Lots of work for not much reason . Normally after a while there is carbon buildup and you would scrape it off carefully ( a de-coke ).
     
  3. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    They're endoscope pics.
     
  4. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    Just looks a bit rich to me. The insulators should stay white for at least 100 miles and it should be cold blooded for a minute after starting.
     
  5. jbruney

    jbruney

    Joined:
    Jan 5, 2019
    Wish mine looked like that..... Put the scope in mine too, but it looked scary so I closed it back up and only check the plugs now.
     
  6. NickZ

    NickZ VIP MEMBER

    Joined:
    Oct 31, 2018
    Thanks for the replies.
    Yes, they are scope pictures.
    So I guess I can conclude that I need to lean it out a little, especially the left side.
    Should I not worry about what is in there? Will it eventually burn off? I definitely don't want to pull the head off if I don't have too.
     
  7. Torontonian

    Torontonian

    Joined:
    Dec 28, 2009
    If oil consumption has settled good after the run in period then I would only lean things out a bit. How many miles on the carbs , needles and needle jets and the needle floats ? If over 10,000 I'd fit all new.
     
  8. jbruney

    jbruney

    Joined:
    Jan 5, 2019
    I'll not share pics of my old girl's gutty works and cause a stir if his gets a rise from any of you guys because to me his are almost pristine.... Then I'm roughly at 22,000mi. with 18k of that on the old lead gas, although a lot of it has been burning out since this switch to unleaded for some reason this country boy can't fathom. True I am rather envious of his pistons appearances and I have no shame, but agree they are a tad rich.
     
  9. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
    IMO the domes on the pistons look “blistered”

    I shall ignore the colour of the spark plugs as this is not a plug chop when at a certain rev range .
     
  10. mdt-son

    mdt-son

    Joined:
    Jan 19, 2012
    Oil and/or carbon fouled spark plugs. I suggest you have your exhaust gas analyzed in order to set the Lamda coefficient correctly. Maybe your plugs are a tad too cold also.

    -Knut
     
  11. norton bob

    norton bob

    Joined:
    Nov 29, 2013
    Do you have any remnants of tank liner in the fuel tank?.
     
  12. NickZ

    NickZ VIP MEMBER

    Joined:
    Oct 31, 2018
    The carb bodies are original (18,000 miles) but I replaced needles, jets and stay-up float kits 100 miles ago. Slides are original, but carbs were honed also during rebuild.
     
  13. NickZ

    NickZ VIP MEMBER

    Joined:
    Oct 31, 2018
    Yes, the blistering look is what concerns me.
     
  14. NickZ

    NickZ VIP MEMBER

    Joined:
    Oct 31, 2018
    Tank was caswelled 100 miles ago. Before that it was original. It did have a bit of running on ethanol fuel last year before I was aware of that issue. That led to the carb rebuild. No ethanol since.
     
  15. cliffa

    cliffa

    Joined:
    May 26, 2013
    It would be interesting to know what’s pooled in the valve pockets.
     
    NKN and Dances with Shrapnel like this.
  16. NickZ

    NickZ VIP MEMBER

    Joined:
    Oct 31, 2018
    How do I check that?
     
  17. cliffa

    cliffa

    Joined:
    May 26, 2013
    I guess the easiest way is leave the plugs out for a few days. If it evaporates it’s gas, if not it can only be oil I suppose.
     
  18. mdt-son

    mdt-son

    Joined:
    Jan 19, 2012
    Piston at or near TDC and using an extended cotton swab may work.
     
  19. Steves

    Steves

    Joined:
    Oct 16, 2016
    I think if you had an oil problem then you would see oil in the first half dozen plug threads. Are you using something like Marvel Mystery Oil? They (pistons) don’t look to bad to honest, see loads worse. Maybe a tad rich (plugs) as others have said. Better too rich than too lean though.
     
  20. norton bob

    norton bob

    Joined:
    Nov 29, 2013
    Those deposits look like tank liner,if it gets on plugs it will not burn off easily.
     
    jbruney likes this.

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