bolt shear caterpillar turbo charger

Discussion in 'Diesel Engines' started by joeshef, Jul 20, 2015.

  1. joeshef
    Joined: Jul 2015
    Posts: 1
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    Location: Florida

    joeshef New Member

    I have experienced failure of the turbo mounting bolts on a 2003 vintage C-12 Caterpillar for no apparent reason. Has anyone has similar experience?
  2. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    The Cat people are pretty good at figuring out what size the fasteners need to be. Two of the most common reasons for failure are: The fasteners were torqued incorrectly. That is true of under tightening and also over tightening.

    The other reason is that the bolts were of inferior quality. There is a big difference in the strength and stretch qualities of the numerous classes of fasteners. Hardware store varieties are made of cheese. Replace highly stressed bolts with grade 8. Available at fastener specialty houses or on line order from firms like ARP who makes some of the most reliable fasteners out there.
  3. Barry
    Joined: Mar 2002
    Posts: 1,668
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    Barry Senior Member

    I would be hesitant to use anything other than what Cat recommends. While a Grade 8 bolt is stronger than say a Grade 5 bolt, generally the Grade 8 bolt will be less ductile and depending on the loading of the bolt, can actually be a poorer choice than a Grade 5.
    Depends on the application

    The threads root cause an extreme Stress concentration and in this application if the bolt were to be subject to bending from loading multiple times, the thread root could work hardened, crack, cause a higher stress concentration then fail.

    Before you run out to a local bolt store you also need to know if the original bolt has a rolled thread as compared to a cut thread.
    Very few bolt stores will stock a rolled thread bolt
    When higher strengths are needed, often manufacturers will often employ a rolled thread bolt which increases the overall load that the bolt can carry and can reduce fatigue issues.

    Buy Cat and hopefully the engineers have figured out the best bolt characteristics for the application.

    An aside, to determine if a bolt has a rolled thread or cut, just run your fingers down the bolt from the shoulder to the thread, if the thread has a slightly higher diameter, NORMALLY, it is a rolled thread.
    Last edited: Jul 29, 2015
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