Why does my woodruff key keep breaking?

Discussion in 'Classic Motorcycles' started by sokol, Oct 1, 2006.

  1. sokol

    sokol Guest

    I'm fairly new to bike restoration so could do with a bit of help.
    The bike I'm working on is a 1936 Sokol, which was a Polish knockoff
    that is basically a 995cc Vtwin a la Indian combined with Harley front
    suspension.
    The problem is that the woodruff key on the kickstart keeps breaking.
    The engine starts fairly easily with no appreciable kick back. The
    advance/retard mechanism of the distributor has been screwed down in
    the maximum retard position and will stay like that until I can
    fabricate the cable for the manual mechanism.
    I'm reluctant to keep on making new keys until I understand why they
    keep breaking.
     
    sokol, Oct 1, 2006
    #1
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  2. sokol

    TMack Guest

    SNIP
    Could this be the clue? If you have made previous ones are you sure the
    dimensions are right? (Do you really mean woodruff rather than cotter pin?)
    Also - woodruff keys are usuallt "belt and braces", the primary "locking"
    being achived by the mating of tapered surfaces. If the surfaces don't mate
    properly then all the stress goes on the key, which may then shear.
     
    TMack, Oct 1, 2006
    #2
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  3. He's right. Lap your taper bits in with fine grinding paste and then make
    sure that your key doesn't interfere with the fit.

    Ron Robinson
     
    R.N. Robinson, Oct 1, 2006
    #3
  4. sokol

    sokol Guest

    In respnse to the various comments

    1. The shaft is not tapered, its parallel.
    2. Dimensions are confusing. The groove on the shaft is 5.5mm while the
    groove on the gear is nearer 6mm. I have no idea if the difference was
    designed in or its just sloppy manufacture.

    Regarding material used and manufacturing technique. I used a bit of
    angle iron which was the closest to 5.5mm and thus needed the least
    grinding down. Also I'm told softish iron is the correct material. it
    should break before the shaft.
    While grinding into shape I dunked the hot item into cold water so that
    I could handle it, did that make it stronger or weaker?
     
    sokol, Oct 2, 2006
    #4
  5. Using the patented Mavis Beacon "Hunt&Peck" Technique, sokol
    If you got it hot enough, it's quite possible that it will have become
    hardened, but very brittle as a result of the rapid cooling. I think
    your problem is the material you're using. Use a piece of decent mild
    steel, and file it to size.

    --
    Wicked Uncle Nigel - Podium Placed Ducati Race Engineer As featured in
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    Wicked Uncle Nigel, Oct 2, 2006
    #5
  6. sokol

    Krusty Guest

    Wouldn't it just be easier to buy one, given the fact you know (or can
    work out) the dimensions? At least you'd know it was made of the right
    material then, & I can't imagine it would cost more than a couple of
    quid at most.


    --
    Krusty
    www.MuddyStuff.co.uk
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    Krusty, Oct 2, 2006
    #6
  7. For a 1936 Polish bike? Googling for 1936 sokol kickstart woodruff
    returned 6 hits. None seem relevant.

    --
    Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration,
    Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN
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    Dr Ivan D. Reid, Oct 2, 2006
    #7
  8. sokol

    Krusty Guest

    No YTC. Woodruff keys come in standard sizes like bolts.

    --
    Krusty
    www.MuddyStuff.co.uk
    Off-Road Classifieds

    '02 MV Senna '03 Tiger 955i '96 Tiger '79 Fantic Hiro 250
     
    Krusty, Oct 2, 2006
    #8
  9. In 1936?

    Although there's a solution. RS sell woodruff cutters, so using
    an appropriate 6 mm cutter to open out his keyway to match the 6 mm slot
    would allow a modern standardised key to be used.

    Metric Woodruff Key Kit, incl. 22x9x6 mm key £16.45
    Whoops, no 6 mm cutter listed... DIYtools.co.uk has a 22.5x6 mm cutter
    for £79.55 -- is that supposed to match a 22 mm key?

    --
    Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration,
    Brunel University. Ivan.Reid@[brunel.ac.uk|cern.ch] Room 40-1-B12, CERN
    GSX600F, RG250WD "You Porsche. Me pass!" DoD #484 JKLO#003, 005
    WP7# 3000 LC Unit #2368 (tinlc) UKMC#00009 BOTAFOT#16 UKRMMA#7 (Hon)
    KotPT -- "for stupidity above and beyond the call of duty".
     
    Dr Ivan D. Reid, Oct 2, 2006
    #9
  10. ordinary angle iron is not going to harden significantly, it'll only be mild
    steel anyway.

    The difference in groove sizes may be related, though. If you're
    hand-making it, you can do a special one which is wider at the top than at
    the bottom.
     
    Austin Shackles, Oct 2, 2006
    #10
  11. You can make a stepped key to properly match the keyways, or have the
    narrower one machined out.
    True. But you then have a slop built in that's going to lead to
    breakage. Have you tried Loctite?
    It would have hardened it to an extent, and it being a small component
    probably embrittled it.
     
    Grimly Curmudgeon, Oct 2, 2006
    #11
  12. To harden steel, you have to a) have the right grade of steel and b) get it
    red hot, then quench it. I doubt either applies in this case.
     
    Austin Shackles, Oct 2, 2006
    #12
  13. sokol

    Roger Hunt Guest

    Evidently Sokol Motorcycles thought it did.
     
    Roger Hunt, Oct 2, 2006
    #13
  14. Using the patented Mavis Beacon "Hunt&Peck" Technique, Austin Shackles
    Well, it could be any old shite, and on a cross-section that small, I'm
    not so sure that hardening wouldn't be an issue.

    --
    Wicked Uncle Nigel - Podium Placed Ducati Race Engineer As featured in
    Performance Bikes

    WS* GHPOTHUF#24 APOSTLE#14 DLC#1 COFF#20 BOTAFOT#150 HYPO#0(KoTL) IbW#41
    SBS#39 OMF#6 Enfield 500 Curry House Racer "The Basmati Rice Burner",
    Honda GL1000K2 (On its hols) Kawasaki ZN1300 Voyager "Oh, Oh, It's so big"
    Suzuki TS250 "The Africa Single" Yamaha Vmax Honda ST1100 wiv trailer
     
    Wicked Uncle Nigel, Oct 2, 2006
    #14
  15. sokol

    sokol Guest

    Thanks to all of you and your input.
    In view of the uncertainty of whether I'm using the right material and
    also whether my manufacturing is accurate enough, I've decided to try
    and buy the damn things.
    Now I've just got to find a source.
     
    sokol, Oct 3, 2006
    #15
  16. sokol

    Steve Guest

    This lot should be able to help : http://www.peterstubs.com/woodruff.html

    Steve
     
    Steve, Oct 3, 2006
    #16
  17. sokol

    Hog Guest

    Hog, Oct 3, 2006
    #17
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