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Norton wheel bearing NM.17721, aka 4203 (2003)

Discussion in 'Norton Commando Motorcycles (Classic)' started by Anonymous, Aug 1, 2003.

  1. Anonymous

    Anonymous Guest

    Anyone have a substitution for the deep-groove double-row wheel bearings (1 fore, 1 aft) NM.17721, aka 4203 in a double-sealed version? I understand there may be a substitution that is 1.5mm wider. Thanks!
     
  2. dynodave

    dynodave

    Joined:
    May 28, 2003
    :arrow:
     
  3. docrecon

    docrecon

    Joined:
    Sep 30, 2003
    Re: wheel bearing

    Thanks DynoDave! Yeah, I'd run across the Old Britt's page and that's helpful, and for now I've decided to take your approach; I bought new single-row sealed bearings from a local bearing supplier as they're not expensive, if my double-rows test out OK I'll repack and go w/ 'em, otherwise I'll go to the sealed ones, Old Britt's prices aren't too bad and I've got the equipment to do the mod.

     
  4. bill

    bill

    Joined:
    Jun 1, 2003
    bill

    try a 5203 at your frindly bearing house

    bill
     
  5. Anonymous

    Anonymous Guest

    Re: bill

    OK, thanks Bill! Both the 5203 and 5203-2RS are 17x40x17.5 vs. the 4203's 17x40x16, thus being 1.5mm wider than the standard bearing. So, the mod would have to be performed to "both ends" to get 'em to work, but w/ the 5203-2RS you'd have a sealed bearing.

     
  6. Time Warp

    Time Warp .......back to the 70's. VIP MEMBER

    Joined:
    Dec 3, 2012
    5203, I machined 0.055" off the spacer (removed material from both sides)
    Now a 2RS bearing is available off the shelf, any time, any where but at a hunch being 60 this year it won't be me fitting the next set of bearings. :D

    s.jpg
     
  7. Time Warp

    Time Warp .......back to the 70's. VIP MEMBER

    Joined:
    Dec 3, 2012
    I machined a couple of alloy spacers to pull the bearings in with a long bolt.

    The hub was warmed in the oven.
    The threaded collar side pulled in until seated followed by the offside.

    I measured around the same as the OldBritts website at 0.056" difference at the spacer top and bearing shoulder in the hub but elected to take 0.055'" off the spacer tube.
    When the double row bearing is pulled in with that alloy spacer it is contacting the inner and outer race of the bearing and will stop when it is in full contact with the hub spacer even if there was a 0.001" air gap under the outer race.
    I personally think that is the safer option and of course the stock 4203 bearing comes no where near seated in the hub.
    I double checked by fitting the front axle and a spacer, torqued to check the bearing rotated smoothly.
    It is possible to fit wheel bearings (not taking into account possible hub expansion with braking heat :D ) and they go from smooth running to notchy when the axle torque loads the inner races and the outer is retained in the hub bore.

    Perhaps there is some merit in running C3's for the extra 0.0005" clearance for that same reason.

    B.jpg
     
  8. Ron L

    Ron L VIP MEMBER

    Joined:
    Feb 27, 2004
    There is a European made 4203-2RS that is 17X40X16 available. Walridge Motors (Canada) has them for $54.40 CD$.
     
  9. madass140

    madass140 VIP MEMBER

    Joined:
    Nov 6, 2011
    why modify your hub when the standard 4203 is readily available? doesnt make much sense to me
     
  10. Time Warp

    Time Warp .......back to the 70's. VIP MEMBER

    Joined:
    Dec 3, 2012
    The hub is not modified in any way Don.
    The hub is over bored depth wise from the factory with a long inner spacer, some measurements and 2 minutes on the lathe reducing the spacer width and done.

    It is almost like it was mean't for a 5203 bearing, no comment on one 4203 for $54.

    It is nothing new and the OldBritts article goes back to 2002.

    https://www.oldbritts.com/wheel_upgrade.html
     
    Last edited: Jun 9, 2019
  11. madass140

    madass140 VIP MEMBER

    Joined:
    Nov 6, 2011
    $54 for a 4203? how about $20. no extra parts needed
     

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