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Cannonball: Broken crank

September 11, 2010

I was on Stage 1, day 1, mile 70 of 3300, riding at 1/2 throttle, going about 30mph, then a sudden bang! bang! bang! from the bottom of the motor.  Clutch in, exhaust valve lifted, I stopped on the side of the road.  While I waited for a chase truck (who was stopped somewhere behind me to pick up some other broken bikes), I started to tear down the motor to see what had happened.  By spinning the rear wheel, the V belt spun the crank pulley and the left flywheel.  The motor would turn over by hand, and the piston was seen to rise and fall after I removed the valve cover.  Valves went up and down as the right side flywheel spun, but there were very audible thump sounds at TDC and BDC…  When I grabbed the hot pulley in my hand, I figured it out.  The pulley could flop slightly from side to side.  The crank pin was broken, but it still made enough contact to spin one flywheel when the other was spun.  I couldn’t get the motor out of the frame right then, as the truck and trailer honked at their arrival.

Loaded, then the long slow drive to the hotel, punctuated by stops to get 2 more broken bikes…  Plenty of time to sit and think and wish that I was riding and not in the truck on the first day of a 17 day rally.  I didn’t have any comfort in knowing that 5 or 6 bikes came in on trucks, or knowing that other motors blew up even worse than mine.  The crank pin was 97 years old, and had done a few thousand miles for me in the last 5-6 years.  But it was time for a new one and I didn’t have a spare in my tool kit.  No damn way was I going to pack up and head for home.

Motor out




Two friendly motorcycle policemen came by the hotel parking lot around 11pm.  While I was tearing into the motor, some of the guys told them about the crank.  Next thing I knew, one of the officers handed me his cell phone and said “here’s a local machinist”!!!  I was elated to hear that somebody was available, but felt a little bad that he was awakened by a call from the police at 11:30 on a Friday night.  After a quick chat, we decided to meet at the shop at 7am Saturday morning to make some new parts.  He did make of point of asking if I was a member of the AMCA.  Sometimes it pays to be a member.DSC08897

Jeff and Tommy at S&S Repair came to the rescue.  The shop does general fabrication and repairs for all types of things, and understands motors.  In this photo Jeff is deburring the new crankpin on the big 16” lathe.IMG_4828

Broken crank pin and new crank pin.   The old one has bronze deposited on the bearing area, from the big end bushing in the connecting rod.  The bushing had spun in the rod, which covered up the holes that allowed oil to splash and drip onto the pin.  The pin seized in the bushing, then the pin sheared.IMG_4862

Old and new pins and bushings.IMG_4869

Big lathe, about 20”


Bigger lathe.  Around 30”.   That round part is the flywheel for my motor.


REALLY BIG LATHE.  About 10 feet in diameter.  This is used to turn parts vertically.  I’m standing at the center of the spindle axis.  S&S uses this to turn parts that weigh several tons.  They also have a 400 ton hydraulic press out back.IMG_4827

Part 2 will come later.  Hopefully I’ll write that the motor came together OK and that I was ready to ride on Sunday for Stage #3.

5 Comments leave one →
  1. Paul Venne permalink
    September 12, 2010 1:01 am

    I actually said a prayer for y’all here in Bangkok in church this morning and lo, the angels have come. Big wow on that fix.
    I remembered I also dropped an exhaust valve on my VW bus once. A small piece of foil came off a duct and sat itself right over the exhaust valve guide blocking cooling air. No flight school that day!! I pulled out the motor, four bolts, onto a tool box and fixed it myself except for the machine shop. Go Pete.
    Best wishes, “overcomers inherit all things,” (Hope I quoted that right.) and thanks for the posts. Paul V MBK shopping mall Bangkok, Thailand

  2. Jim Abbott permalink
    September 12, 2010 10:18 am

    Pete: Able to leap tall buildings in a single bound!!

    Since I can’t get anybody to drive with me and ferry the car/trailer, I will try to drive to S.M., leave the car/trailer there and begin stage 16 backwards till I meet up with you all. I am pretty sure you’re not using the major highways/freeways so I don’t know the route you will be taking. Is there any way to find that out?

    To quote pd’o (and Oscar Wilde) “yours, lying in the gutter, gazing up at the stars”, Jim A.

  3. Richard McKenney permalink
    September 12, 2010 9:43 pm

    G’day Pete

    Sorry to hear your bit of bad luck, hey maybe your in for the Hard Luck Trophy?

    The picture of the machinist nabbed by the coppers is a cracker, one for the shed wall!

    Go for it Pete, you know there’s a ride across Australia coming up?

    Cheers Richard

    • Pete Young permalink*
      September 13, 2010 6:50 pm

      thanks Richard. He’s not the machinist though! One of the guys in the parking lot around midnight that night when the cops called in for help.

  4. September 13, 2010 10:36 am

    Ouch! Nice official help you got. Very cool.
    Nice industrial shop the S&S boys have. Sweet.

    Great to see you got some “good old boy” help. Cause that’s what were good at. 🙂 We’re gooder.

    Being in a shop also allows you to check and true a few things (properly) before assembly.
    I’m so happy you got this help. Really nice to see.

    That O. Wilde quote is great by the way.

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