A lesson in humilty.

Discussion in 'Airheads' started by Jim Day, Apr 18, 2013.

  1. Jim Day

    Jim Day full manic mechanic

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    So I figure I might as well fess up. If you saw my R65 customization... http://www.advrider.com/forums/showthread.php?t=858426&page=2
    [​IMG]

    Well.... It's performed pretty much perfectly, honestly better then I expected, a blast to ride and I love it... That said: the other day I was doing some high speed stability testing and the drive shaft failed.

    I figured I was running in the high eighties, later inspection of my GPS said a decade more and though it tracked straight as an arrow with no vibration and even made it home, a few days later when I fired it up I heard some noises like the splines failed, and quickly realized that the forward weld on the drive shaft has failed.

    In some thirty years of welding I can't recall a structural failure, but there's always a first time, and I could of hit it a little harder.

    Haven't pulled the swingarm apart yet, so my biggest curiosity is if the shaft itself bent.

    If not I'll just grind it back an re weld it, fortunately since the original shaft is pinned into the extension it never flopped around but spun on a pin if you will<and to="" be="" honest="" i="" could="" of="" hit="" it="" harder="" for="" more="" penetration.
    . So it's still there just slipping at the snapped weld.

    I just want it back on the road before the deus ex machina ride Sunday.


    Hey if I was perfect if I'd run this place. :lol3

    Jim</and>
    #1
  2. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Such is the price of R&D. At least you got out and did something instead of being an internet armchair warrior. Find out why the weld failed so it won't happen again. It could have turned out much much worse.

    Neat work on the bike, BTW...

    --Bill
    #2
  3. Beater

    Beater The Bavarian Butcher

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    Can you describe your methods of welding? Also how did you put the shaft together? You balanced it?

    :ear
    #3
  4. Jim Day

    Jim Day full manic mechanic

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    I MIGed it at a relatively high heat using CO2, perfectly straight.

    I first took some stock, cut it to length, then drilled out approximately 1 1/2 inches into each end, 3/8 of an inch on center to make the extension.

    I then reduced the diameter of the original driveshaft down to approximately 3/8 of an inch for a few inches.

    http://youtu.be/05e5LG8ZADg

    I then cut the shaft in half in the middle of the reduced portion and slid each end into the extension.

    [​IMG]

    That's it before the welding.

    I then blocked it up with some bars and V blocks and like I said I MIGed it. I then put it in a lathe to check for balance.

    Between you and I.... If you look at the pic again. I ground it back a little more then that. but I could of ground back more steel for deeper penetration. It's the classic lazy welder thing. I compensated for grinding which I hate with welding which I enjoy.

    In hindsight that was maybe an error, and I could of also used a stronger steel stock as well.

    My take though after lathing the shaft was it's not really all that hard, so I thought the stock I used was more then adequate..

    Are you an engineer? I think I get where you are going. If it was slightly out of balance it would move the most at the end with the universal as the other end is fixed. More movement more metal fatigue more chance of failure.

    What you also might find interesting is that I've torqued it very hard climbing hills etc... but it's the high RPM that took it out. That would suggest it was balance.

    That said it was perfectly straight, and turned clean on the lathe.

    Now I got a question for you. At 7000 engine RPM how fast is that shaft turning?

    My take is I'm going to make it work no matter what. Having a weld on the shaft fail is not a big deal compared to the splines or gearbox, I can fix it for nothing, and at least the swingaram is aligned and the bike rides straight with no adverse movements or vibration.
    #4
  5. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    I'd be curious to see how and where the driveshaft failed. It looks like you did everything properly and, let's face it, you're only pumping 50-60 HP out of the engine.

    --Bill
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  6. Beater

    Beater The Bavarian Butcher

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    Yes sir. An Engineer, but the 'wrong kind'. Chemical. :lol3

    You seem to have the issue I thought I'd have ... penetration to the center of the shaft. High heat MIG would only get the first 1/8 or so of the shaft. This is one of the reason HPM uses friction welding of shafts.

    As for how fast it was turning ... because the shaft is attached to the transmission, it depends on what gear you were in. In reality, it's relationship will be more about the speed of the bike and not the RPM of the engine. If you were doing 'high 80's' ...

    What is your final drive?

    PS - Good to see someone doing this kind of modifation! BRAVO!
    #6
  7. Airhead Wrangler

    Airhead Wrangler Long timer

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    Turn both shaft ends down to a point and chuck them up in your lathe to weld them. Get a good deep V groove for the joint and try to weld it all the way from the very center out.
    #7
  8. ericrat

    ericrat Long timer

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    Gear ratios are 4.4 / 2.86 / 2.07 / 1.67 / 1.50 : 1

    So for 7000 RPM I come up with
    3rd 3381
    4th 4191
    5th 4666

    BTW, I calculate 7000 rpm with standard R65 gearing/final drive and a 100/90 tire is right at 100MPH. Which in my experience is pretty much out of breath for an R65.
    #8
  9. Jim Day

    Jim Day full manic mechanic

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    Yeah no doubt if it's failed the way I think it has it's a lack of penetration of the weld. I should of ground it back more to get more penetration. Of coarse I'll know more when I get it apart. :freaky
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  10. Beater

    Beater The Bavarian Butcher

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  11. Jim Day

    Jim Day full manic mechanic

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    Yeah well... without admitting culpability it was all in the realm of testing and science.:shog
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  12. bpeckm

    bpeckm Grin!

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    ...wow...!!

    Now THAT is a visual and graphic demonstration! Thank you, I had NO idea that could be done....!

    :D
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  13. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    #13
  14. KhaoSanMan

    KhaoSanMan Airhead

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    Try hard, Fail Harder!
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  15. Padmei

    Padmei enamoured

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    Best thing about this fault is it creates a good discussion for future successes for others- keep up the good work.
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  16. Beater

    Beater The Bavarian Butcher

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    +1 This is exactly the discussion I'd like to have.

    :ear
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  17. Warin

    Warin Retired

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    Wrong question :evil

    You can pull the clutch and kill the motor and the drive shaft will still be spinning if you are moving down the road.

    As the drive shaft is directly connected to the rear wheel through the bevel drive the speed of the drive shaft is directly related to the bikes speed (via the wheel circumference and the bevel drive ratio.

    If you went to a larger diameter shaft that slipped over the original shaft (without machining it) then you'd have a slightly stronger effective joint - the stress is related to the radius of the wielded joint. Provided it fits down the swing arm... ?
    #17
  18. KustomizingKid

    KustomizingKid Been here awhile

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    Shoulda tig welded it...
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  19. chollo9

    chollo9 Screwed the Pooch

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    I have not failed, I have merely found 10,000 ways that do not work. Thomas Edison
    #19