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850 max bore - what then?

Discussion in 'Norton Commando Motorcycles (Classic)' started by fiatfan, Aug 14, 2019 at 11:34 AM.

  1. fiatfan

    fiatfan VIP MEMBER

    Joined:
    Aug 9, 2015
    My 850 is bored out +0,060" and that seems to be the biggest oversize? I´m gonna measure it first of course, but if it turnes out that I need to bore it even bigger, like + 0,080" like the 750 cc, it doesn´t seem to be pistons in that dimension. Is it possible to get a pair of 880 cc pistons from somewhere? Can´t find any of those either.....Or is the only option to buy new or used barrels? I guess you could have them sleeved but if that´s economicly sane I don´t know.
    Tommy
     
  2. SteveA

    SteveA VIP MEMBER

    Joined:
    Dec 20, 2011
    I had a pair of barrels sleeved. They are currently fitted to my race bike. It was economically very sane!

    I had them done through Norman White and had another pair of barrels bored +20 at the same time.

    I have another pair of barrels with sleeves, they are 920, 81mm. To use them you need to open the crankcase mouth.
     
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  3. marinatlas

    marinatlas

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    Nov 4, 2007
  4. Fast Eddie

    Fast Eddie VIP MEMBER

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    Oct 4, 2013
  5. Craig

    Craig VIP MEMBER

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    Dec 20, 2005
    no such thing as stumped on this forum , always different ways to skin the same cat
     
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  6. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    I am under the impression that the bit between the two cylinders is what limits the oversize you can use. If you sleeve barrels to make a 920, aren't the sleeves touching and depend on each other to be held in place ? Also what you pick up on the hurdy-gurdy, you lose on the merry-go-round. Bigger bore sometimes means heavier pistons, which have to be decelerated and accelerated at the top and bottom of each stroke. So the motor spins-up slower. If you fit lighter pistons into a motor and do nothing else, the performance boost is quite noticeable.
     
  7. lcrken

    lcrken VIP MEMBER

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    Mar 15, 2009
  8. ashman

    ashman

    Joined:
    Jul 11, 2010
    Resleeve to stock and start all over again.
     
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  9. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    Or have them Nickasil coated.
    You could then stay at .060 with a nice hard long wearing surface that cools better than a sleeved barrel. Jim
     
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  10. MichaelB

    MichaelB VIP MEMBER

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    Jan 14, 2004
    Have a cool running 880...
     
  11. fiatfan

    fiatfan VIP MEMBER

    Joined:
    Aug 9, 2015
    I always thought that was only done to twostrokes, but it works well on a Norton too? Do you have to change something else for that to work?
     
  12. fiatfan

    fiatfan VIP MEMBER

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    Aug 9, 2015
    Marineatlas and Fast Eddie; sometimes I amaze myself how bad I am at finding stuff on the net......Thanks.
     
  13. Matchless

    Matchless

    Joined:
    Dec 23, 2010
    Jim, Just how successful is the Nicasil process when used on iron as opposed to aluminium. I looked into this for my AJS twin but the company I contacted seemed reluctant to coat iron.

    Martyn.
     
  14. Klaus Monning

    Klaus Monning

    Joined:
    Nov 27, 2014
    Hello,
    I simply got my barrel bored to +0.80 (79mm) and use the Taivanese pistons with Hastings- rings. These are offered by RGM, MAP and others. Also they have different names like "New Hepolite" EMGO etc. Now about the quality:
    I measured diameters (left and right), compression height, wall thicknesses, etc.
    All these dimensions were absolutely equal. Also the weight- difference between the 2 pistons was nearly "0". I can honestly say that the quality of those pistons is just as good or even better then the one from the old Hepolites, AE, etc. I even had a full throttle blast, for e few kms along the German Autobahn and no problems.
    Now again the question: there are so many automotive parts made in China, India, or Mexico. They all fulfill the quality- specs. of today's car manufacturers. Why should they not be able to supply sufficient quality for our old bikes? I'm absolutely certain that they are.
    BUT, CERTAINLY RACING PARTS ARE A DIFFERENT MATTER ALL TOGETHER.
    Best Regards
    Klaus
     
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  15. Klaus Monning

    Klaus Monning

    Joined:
    Nov 27, 2014
    Something else I forgot. Somebody told me that liners are made from centrifugal cast iron, which should be of a better quality then the standard cylinder. So it is also worthwhile thinking of re- sleeving the cylinder. In this case you start with a new standard bore of 77mm for the 850.
    Best Regards
    Klaus
     
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  16. Matchless

    Matchless

    Joined:
    Dec 23, 2010
    I would agree regarding the Taiwanese Hepolites. I put a set into a T150 a few years ago & as always I measured & weighed them first. They were all the same dia. to within 0.0002", all the same weight & also beautifully machined. The rings on the other hand were crap. The engine smoked badly so I fitted a set of rings from Norman Hyde, Goertze I think, & the smoking stopped.
    I sold the bike to a friend & it is still running perfectly after many miles.

    Martyn.
     
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  17. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Commando barrels are not steel, but cast iron. Would Nikasil stay attached ? Nikasil on aluminium might be good, but not if you are running methanol.
     
  18. lcrken

    lcrken VIP MEMBER

    Joined:
    Mar 15, 2009
    Nickel Silicon Carbide coatings work fine on cast iron cylinders. U.S. Chrome does their version, "Nicom", on aluminum or iron bores. More info here:

    https://www.usnicom.com/StreetBike/CylinderPlating

    Nitriding also works well for iron bores, either conventional nitriding or ion-nitriding. Back in the '70s, Norton nitrided the bores of their iron cylinders in some of their 750 short stroke race bikes. I used one of them in my race bike for years with no noticeable wear. It would probably still be in use if it wasn't for that broken (factory steel) rod.

    Ken
     
  19. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    Nikasil works well on an iron bore. It wears better than iron and dissipates heat better than sleeves.

    Nitriding also works but you can not repair a worn or damaged bore -only make it more wear resistant.

    Sleeves are spun cast in either gray iron -similar to the original barrel without the porosity problems of gravity cast
    or
    Nodular iron which is much stronger and more wear resistant than gray iron.
    Nodular iron liners are tough on standard Norton iron piston rings but work well with chrome rings.
    I just installed a pair in Sir Eddies Rocket engine.

    .080 over pistons are fine in most 850 barrels but some barrels with a little extra core shift may end up with thin spots or cracked spiggots.
     
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  20. fiatfan

    fiatfan VIP MEMBER

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    Aug 9, 2015
    I had this done by a small company 50 km from where I live, they had to sleeve one cyl in a small straight 6 for one of my cars. Worked out great, so that´s absolutely an option.
     

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