Advice on refacing a bearing journal please

  1. dyno-tron

    dyno-tron Member

    Messages:
    282
    Location:
    Near Chester, UK
    Hi Peeps,

    The attached pic is of a crank half from a 100cc racing engine (not the actual one I need to work on but basically the same). The main bearing journal nominal size is 20mm diameter, the minimum size due to wear before it is considered scrap is 19.95mm. The one I want to repair is 19.90.

    Refacing is not permitted for racing - no mods, machining or additional metal allowed.

    However - for a playtime engine it will rejuvinate an otherwise scrap engine, the reason this engine would be scrap is 'cos a new crank assembly is approx £500 and this engine with a new crank fitted would be worth approx £250 - go figure!! (BTW - a brand new engine is approx £1800).

    As it is otherwise scrap I'm going to have a go at refacing the journals :-))


    So - the question, could someone advise what welding rods to get please, I probably only need a couple? what amperage? any pitfalls?

    I don't know what grade steel the crank is, just that it is "special grade" maybe EN24 at least, quite tough, spins up to 16K. the bearing that this journal rides on is a standard type deep groove ball bearing and it is a "sliding fit", e.g. snug fit and can be separated by hand, that is why the damn thing wears down :-(
    crank.JPG

    Any advice gratefully received :thumbup:
     
  2. RonA

    RonA specialist in repairing sealed for life equipment

    Messages:
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    Location:
    Stockton on Tees, UK
    Worth investigating if any local engine refurbishers offer this service, might avoid stress build up from normal welding

    RonA
     
  3. Seadog

    Seadog Forum Supporter

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    A light knurling and use bearing-fit adhesive.
     
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  4. hotponyshoes Member

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    Speedisleeves (not sure on the spelling?)
     
    metalmelt, fizzy and mike os like this.
  5. Feet 'n Inches

    Feet 'n Inches Out of the rat-race at last

    Messages:
    364
    Location:
    Devon, GB
    That beats the old way of building up the shaft pad-welding style. How long would that technique last compared to building up and turning back to size?
     
  6. mike os

    mike os just a little insane.....

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    7,003
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    oversize bearing?
     
    tom2207 and fizzy like this.
  7. MoreWellie Forum Supporter

    Messages:
    1,270
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    Bedfordshire, UK
    rather than spend money on this crank save yourself some time and buy an engine that someone else has fitted a new crank to
     
    metalmelt, slim_boy_fat and ronan like this.
  8. Brad93

    Brad93 M J B Engineering

    Messages:
    10,397
    Location:
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    You need spray welding you’ll warp the whole lot it you build up with TIG/Stick
     
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  9. minimutly Member

    Messages:
    1,510
    Location:
    Pembrokeshire Wales
    I wouldn't knurl it - your pressure absorbing contact area is reduced. Years ago I used to have pump shafts built up with spray transfer - they would work but quickly fail - the metal was too soft. This may have improved by now (30 years...)
    If you weld it you will get shrinkage/stress etc, but maybe that doesn't matter too much?
    Why is there an oilway in there? If you weld I would plug this first and redrill after from behind.
    When you've done it do you want a go at my vmax crank?
     
  10. Brad93

    Brad93 M J B Engineering

    Messages:
    10,397
    Location:
    Essex
    Someone using the wrong powder. The powders havent changed in 40-50 years.

    there’s a bonding/buttering later and then a journal surface, usually high in nickel so pretty tough.
     
    minimutly and rory1 like this.
  11. MoreWellie Forum Supporter

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    1,270
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    Bedfordshire, UK
  12. dyno-tron

    dyno-tron Member

    Messages:
    282
    Location:
    Near Chester, UK
    Yeah, unfortunately there are none for sale otherwise that would be the best option.
    It's not my engine, just trying to get something working for a mate :-)
     
  13. dyno-tron

    dyno-tron Member

    Messages:
    282
    Location:
    Near Chester, UK
    Yes - it is, but this needs both sides replacing and maybe a Conrod (may get away with the current one, subject to measuring when it is disassembled)
     
  14. dyno-tron

    dyno-tron Member

    Messages:
    282
    Location:
    Near Chester, UK
    There is no oilway, just a trick of the light/photo
     
  15. dyno-tron

    dyno-tron Member

    Messages:
    282
    Location:
    Near Chester, UK
    The one in the pic is very dead, big end journal is cracked, so I may have a practice on this one as a proof of concept, thanks everybody for your input!!
     
  16. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

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    dyno-tron and Kram like this.
  17. ronan

    ronan Forum Supporter

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    10,276
    dublin
    Send it to Alpha bearings in Dudley.
     
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  18. frank horton

    frank horton V twins are great but 4"s rule.........

    Messages:
    2,230
    Location:
    Soon 2 B Crete
    seen them hard chrome and regrind back to standard......
    look in Motor cycle mags...think the place is in Luton, Beds.....
    not cheap but no heat needed and the uncertainty it causes.......
     
  19. Pete.

    Pete. Member

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    9,817
    Location:
    Kent, UK
    I'd go around that with a sharp centre punch making a grid-pattern of dots then press the bearing onto it.
     
  20. Matchless

    Matchless I started with nothing, still have most of it left

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    I think he died, forgotten his name!
     
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