How Much Should It Cost To Get A Crank Turned Undersized And Polished?

Discussion in 'Rotating Assemblies' started by Grumpy, Feb 29, 2020.

  1. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    I get questions like this all the time,
    generally when someone spun a bearing and ,
    would prefer to not buy a new crank,
    and the answer always depends on the crank in question,
    the material, its made from,
    the machine shop you deal with,
    and theres factors like,does that machine shop have the tools and experience required,
    or will they sub out the job and send out the crank?
    is it one or all the bearing journals,
    that needs to be machined, "welded" polished'
    and remember welding can induce stress,
    done properly on a mild steel crank and ,
    checked for straitness, and carefully polished it will be just fine.
    nitrated or cast cranks, well, in my experience,
    that lowers component durability over the long term,
    if its not done correctly.
    its common for the thrust bearing face to need to be rewelded,
    after years of hard use, and that is generally not any problem.

    is the crank built with surface hardened journals?
    is it cast or forged? how old is the crank?
    were any previous repairs done?
    how common is the engine?
    how long will the repair work take?
    and believe me when I say, a machine shop estimate that sounds like
    "we can probably get to it next week"
    we won,t really know how much until we test and measure.

    generally results in several weeks to a month plus down time,
    and a bill that makes you want to strangle the guy at the machine shop,
    so buying a new crank is frequently the smarter route.
    in many cases like with a cast SBC ,or sbf ,
    its generally faster and cheaper to either look for a good used replacement or to buy a new crank,
    and many machine shops will have used cranks in inventory that they may be very willing to sell you,
    at a significant discount if your getting other work done.
    after all if the used crank had been though a few million stress cycles, over tens of years and it ,
    might cost several hundred dollars to rebuild, it makes a great deal of sense to go out and buy a new crank.
    to answer the question I would suggest you price a new replacement crank, and then,
    go out and drop by at least two or three local machine shops for a quote,
    be fully aware that most will advise you that there may be un-obvious damage,
    that you should have the crank magnetically or dye tested for flaws,
    and it may need to be rebalanced and polished,
    most of the local shops charge $230-$400 for your average crank repair and a balance job ,
    frequently adds an additional $120-$200,
    keep in mind a new crank may cost less and even if its slightly more,
    it won,t have under gone millions of previous stress cycles

    related threads you should read
    Last edited: Jan 9, 2021
  2. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

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