Crankshafts Crankshaft Design The crankshaft converts th

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Crankshafts
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Crankshaft Design

• The crankshaft converts the linear
  (reciprocating) motion of the piston into a
  rotary motion that can be transmitted through the
  driveline
• Crank throws are position around the centerline
  in a manner that provides smooth power output
• The firing order of the engine is determined by
  the crankshaft as well as the camshaft

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Crankshaft Materials

• Cast iron
• Cast steel
• Forged steel
• Nodular iron
• Malleable iron
• Billet steel
• Titanium

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Forged vs. Cast

• Cast cranks are more economical, but are more
  brittle and susceptible to breakage
• Cast cranks are generally lighter that a
  comparable forged one
• A cast crank will have a narrow parting line
  whereas a forged one will have a wide parting
  line

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Forged, Cast and Billet Cranks

1. Cast crank has thin parting line
2. Forged crank has wide parting line
3. Billet crank has no parting line

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Crankshaft Steels

• 1010 --Standard alloy steel, one step above
  nodular iron.
• 1053 --One strength-level better alloy, used in
  high-performance crankshafts.
• 5140 --Excellent alloy steel, a compromise
  between strength and price.
• 4150 --Much more durable alloy, yet not quite as
  strong as 4340 alloy.
• 4340 --Premium-grade alloy steel used for
  ultimate-performance cranks in both forgings and
  billet. Standard for aerospace and diesel
  industries.

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Surface Treatments

• Surface treatments are used to improve wear
  characteristics of crankshaft journals
• Surface treatments only affect a shallow area and
  if the crank is ground it must be re-treated to
  retain the same surface hardness

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Surface Treatments

• Nitriding (Tufftriding) A shallow heat-treating
  process that case-hardens approximately
  0.005-inch deep into the base alloy. This
  preferred process does not use excessive heat,
  allowing the crank to flex more easily without
  creating stress cracks. If a nitrided crank is
  machined, it often needs to be renitrided to
  replace the removed case hardening.

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Surface Treatments

• Deep-Case Nitriding An older heat-treating
  process that hardens the material to a greater
  depth. Deep case-hardened cranks often cant be
  repaired.
• Hard Chroming An electrolytic process that
  deposits chromium on metal. This differs from
  flash chroming (like we find on bumpers), which
  is more of an overplating. Hard chroming creates
  a 0.010- to 0.030-inch-thick surface that
  improves wear, corrosion, and heat resistance

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Crankshaft Features

• Journals The machined surfaces on which the main
  and rods bearings ride
• Journal fillet The area where the journal meets
  the crank web. This fillet adds strength to the
  crankshaft and is a common area for cracks to
  develop

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Crankshaft Features

• Counterweights Used to balance the rotating
  assembly
• May be internally or externally balanced
  (externally balanced engines will use a offset
  balance harmonic balancer and/or flywheel)

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Dennis Wells on Crankshaft Balancing

• Circle track magazine interview
• Dennis Wells of Wells Racing Engines is familiar
  to Circle Track readers. His day-to-day work with
  and on circle-track engines often brings
  practical and valuable insight to the weekly
  circle tracker. I asked him to expand on points
  about crankshaft selection.
• Why do you think crankshaft balancing is
  important?
• Clearly, engines need to be balanced during the
  build-up process. There are dynamic forces that
  exist in a running engine that probably exceed
  what many of us might think. Heres an example of
  forces applied on the crankshaft. At four inches
  from the crankshafts axis and with 28 grams of
  unbalance, theres 112 pounds of force at 4,000
  rpm. This increases to 448 pounds at 8,000 rpm!

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Dennis Wells on Harmonic Balancers

• How important do you consider crankshaft dampers,
  and why?
• Crankshaft torsional vibration causes crankshaft
  and flexplate failure, bolts loosening, timing
  chains to break and valvetrain and erratic
  ignition problems. We tested our USAC Silver
  Crown car on the wheel dyno. We removed an ATI
  lightweight damper, installed a small, aluminum
  hub and made five consecutive runs. We saw no
  horsepower gains. What we discovered when
  removing the aluminum hub was that the torsional
  vibration, in only five runs, was so great that
  the hub was no longer a press fit. It slid off by
  hand! How much more proof could you want?

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Dennis Wells on Crankshaft Installation

• Whats on your list when it comes to crankshaft
  installation and maintenance?
• Always inspect a crank closely before performing
  any machine work. This includes checking
  straightness, thrust surfaces, checking every
  journal for taper, size and roundness, confirming
  the stroke, and passing Magnaflux inspection.
  Remember, everybody can make a mistake you just
  need to catch em. Its easier to correct any of
  these problems before you waste your time
  balancing, or worse, building the engine and then
  finding out something is wrong. You must use
  chamfered bearings on cranks with a radius larger
  than 0.062-inch. And you must mic everything
  and check every bearing housing for size and
  roundness

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Crankshaft Features

• Rear flange used to mount flywheel/flexplate,
  may contain a bushing or bearing to locate the
  input shaft or torque converter
• Crank snout Used to mount the cam drive gear
  and the harmonic balancer

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Harmonic Balancer

• Cancels torsional vibrations and oscillation
  creating by the engine
• Stock dampers consist of an inner hub, a rubber
  slip ring, and an outer hub with an ignition
  timing mark
• High performance dampers may use a dampening
  fluid contained in a steel shell
• When reusing a harmonic balancer, be sure to
  degree it to assure ignition timing accuracy
• Externally balanced engines may use an unbalanced
  harmonic balancer

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Crankshaft Measurements

• Size
• Taper
• Out of round
• Runout

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Crankshaft Repair

• Regrinding may regrind just mains, just rods or
  both
• Polishing removes minor surface imperfections
• Welding journals may be built up by welding and
  reground
• Storage store upright