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crankshaft radius

Discussion in 'Norton Commando Motorcycles (Classic)' started by John leathers, Mar 24, 2015.

  1. John leathers

    John leathers

    Oct 24, 2014
    Just got the crankshaft back from engine shop and found that they had ground 10 thou of crank and also of the radius.now the journals are ground at right angles. Any help would be great. Bike is 1971 commando 750, I should have copied the workshop manual when sent to engine shop cheers john
  2. concours

    concours VIP MEMBER

    Dec 29, 2011
    Hi, Welcome. Sounds like you know what to do... Send it back to them, have them re-establish the radius. Or, if they went too wide, then, well, um, crap, we can't ever "grind a little ON"
  3. Peter R

    Peter R

    Dec 13, 2010
    The right angles will work as a stress raiser, and seriously increasse the risk of crankshaft breakage.
    I know my words do not offer much comfort, but you should never have this job done by a shop that is not familiar with Nortons.
    I have no idea know how to solve this, other grinding the crankshaft again if this is possible , and if not, than you should explain to this shop that they messed up your crankshaft, and demand financial compensation.
  4. lcrken

    lcrken VIP MEMBER

    Mar 15, 2009
    Unfortunately, there's no way to regrind the crankshaft to get the .090" radius back without making the side clearance huge, or grinding the journal WAY too small. You need a replacement crankshaft.

  5. Nater_Potater

    Nater_Potater VIP MEMBER

    Apr 7, 2013
    It's possible that the journals could be flame-sprayed and then ground to size, but the cost may be prohibitive (for your machine shop). There's a number of businesses out there just for this operation. http://www.mbicoatings.com/content.cfm/ ... age_id/171 is just one example. You might try getting a quote from them and forwarding that onto your machine shop. My condolences...

  6. hobot


    Oct 19, 2005
    Ken Canaga found Peel's nitrided crank too bent-distorted and too undersize ends to use so considered it trash till I found this place that recovered fast and cheap and correct. Ping em to see what they might be able to do on fill in to radius.
  7. Matchless


    Dec 23, 2010
    What about an undercut fillet radius as used on modern cranks. These are rolled using pressure to increase strength. Even grinding this into a Norton crank would be better than no radius. It might just be worth a try. If not, it's the scrap bin!
  8. mike provence

    mike provence

    Oct 24, 2004
    Hard chrome and regrind. A good hydraulic marine machine shop should be able to do it. Call out the radius.
  9. toppy


    Dec 2, 2012
    The stress raising sharp corner is in the base metal of the crank it's self and so building up with chrome or other types of coating will not improve the strength of the component just hide the problem from the eye.
    The amount of metal that will need to be removed to reform the radius will also affect the strength of the component so best action is to replace it and see if the machine shop will come to some agreement with you about the cost..
  10. mike provence

    mike provence

    Oct 24, 2004
    Right. I stand corrected. No buildup would correct the stress riser or underlying problem.
  11. Rohan


    Aug 26, 2010
    This is not strictly correct - correctly applied hard chrome, or flame applied metal powder, becomes PART OF THE METAL, and should correct the problem.

    I've seen craftsmen flame welding cranks on the footpath in India.
    And having previously travelled in a Bedford bus that was in its 5th reincarnation at least,
    can vouch that such crankshaft refurbs can work well..
  12. toppy


    Dec 2, 2012

    I have seen chrome repairs done by skilled men fail and does a bus crank have the inherent weak point that calls for the rad in the first place. Also does it spin at the same speeds as a Norton crank. I am full of admiration of the skill and ingenuity of people in poor countries who can keep things going with no tools or spares but they only need to make their bus move an that's all they care about.

    I would not put the crank in my engine as i would always be worrying about the crank and trying not to stress it. If it fails then it will need replacing and so will many other things that will be damaged when it lets go. So its safer and cheaper to replace it now but it is obviously not a pleasant experience or cost you wished to spend.
  13. Rohan


    Aug 26, 2010
    Find a shop that can do it for aircraft engines, and they will know what that are doing.
    It won't need all the paperwork either, so the cost won't be excessive.

    These process are commonly used in agricultural equipment, sometimes even as oem,
    big horsepower, so it works...

    The norton crankpins are good quality steel, so will take a good weld job.
    Avoiding distortion is where some experience will come into it.

    And if the crank is scrap otherwise, nothing to lose seeing if it works out OK.....
  14. peter12


    Jun 18, 2013
    Whatever you do don't leave it, had a crank break in the 80's.
  15. comnoz

    comnoz VIP MEMBER

    Dec 10, 2008
    Welding could fix it if it was done correctly. Of course the only way to know if it was successful is to see if it breaks.

    Hard chrome would likely make the problem worse due to hydrogen enbrittlement. It would add no strength to the fillet.

    Norton cranks are not so hard to come by. I would get another one and start over with someone who knows what they are doing. Jim
  16. Rohan


    Aug 26, 2010
    The hardchroming doesn't need to 'add strength", it simply needs to add material to the
    parent metal so the stress reducing radius can be ground back into the crank. (?).
    Heat treating to remove H2 embrittlement is routine part of hardchroming cranks.
    Not that hardchroming introduces much of this anyway.
    This is not exactly new or untested technology...
    Likewise, flame welding to reclaim cranks etc is an extremely common procedure, many industries do it.
    Some as oem manufacture.

    I'm sure an aircraft welder could be found that is more than familiar and capable of doing this.
    That fleet of footpath craftsmen maintaining an ancient fleet of buses could probably teach us a thing or 2 too.
    A refurbed crank on its 10th ? incarnation hauling a few tons of passengers has been truly well tried and tested...

    Whether this is cheaper than simply finding another (good) crank is another matter....
  17. Anonymous

    Anonymous Guest

    Reclaim the current crank and grow an ulcer every time you ride your bike, or
    Find a good one and ride with confidence that it won't crackup/lockup midway though a high speed corner beside a sheer dropoff.
    Tough choice - your choice, I say.
  18. Rohan


    Aug 26, 2010
    Crankshaft shops and aircraft welders do this sort of stuff all the time.
    Its exceedingly likely you've flown on a plane with something vital welded.
    Do pilots look worried. ?

    Only if they are feeling suicidal lately, it seems.

    Didn't we see hobots welded crank recently, with provision for screwed in weight plugs.
    Whats the difference, when it comes down to it....
  19. Anonymous

    Anonymous Guest

    Indian footpath welders are kept employed by:
    A. Fixing pristine crankshafts that just broke?, or
    B. Bodging up bodged-up crankshafts that keep breaking at the previous bodgy welds?

    Original poster: Longevity of your crankshaft is directly proportional to your longevity, choose wisely.
    "They said it would be ok" is not a great tombstone inscription.
  20. Rohan


    Aug 26, 2010
    Silly words ?

    Indian footpath welders were refurbing cranks that had done millions of miles.
    They flame welded them up, and then the extensive machine shop inside ground them back to std.

    The old Bedford I had travelled in was 1953, , across a desert, I was told that it had been travelling that route ever since.