Running-in recommendations for replacement big end bearings

Discussion in 'Engine maintenance, upgrades and modifications' started by M3 Convert, Aug 2, 2019.

  1. 2 Aug 2019 at 3:11 PM #1
    M3 Convert

    M3 Convert A mere Chipper

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    I'm planning on having my conrod (big end) bearings replaced as a precautionary measure. I'm guessing running-in will be a case of not allowing the engine to labour, not to exceed about 3000 rpm with the engine cold (what I always do anyway) and not to exceed about 4000-5000 rpm for the same miles as the original running-in service. Then, change oil and gradually increase the rev limit on a fully-warmed engine.

    Does this sound about right ?
     
  2. 2 Aug 2019 at 3:19 PM #2
    tsinc

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    Shouldn't have to run in new bearings.
     
  3. 2 Aug 2019 at 6:30 PM #3
    m3rosco

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    No need to run in.

    The running in period is to allow the piston rings to bed into the bores.
     
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  4. 3 Aug 2019 at 5:58 PM #4
    M3 Convert

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    OK, understood, a stupid question possibly. I appreciate running in being primarily related to piston rings needing to "bed in" whereas bearings being essentially non-contact (necause they are running in/on a very thin film of oil) so less relevant. However, surely it's sensible to "take it easy" for the first few hundred miles or so after fitment ?
     
  5. 3 Aug 2019 at 6:00 PM #5
    tsinc

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    Nope. Crack on.
     
  6. 6 Aug 2019 at 11:41 AM #6
    Jimbo25

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    Wouldn't be a bad idea to drop the oil and change the filter a little sooner just in case during the strip/rebuild any dirt has found it's way into the engine, that's probably the biggest thing. Bearings do bed in to a degree, but not to the extent as piston/bore interface which tends to mean material gets dragged into the oil. More to do with the surface of the bearing hardening and accepting any tiny amounts of material (as they're designed to do) so as long as you're not bouncing it off the rev limiter or doing 8,000 rpm before changing up on the first day then you should be OK.

    Never a bad idea to drive it carefully with an eye on temps, leaks etc for the first few days.

    Personally I would drive a little more restrained than normal for 500 ish miles but that's just me.
     
  7. 9 Aug 2019 at 1:14 PM #7
    M3 Convert

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    Thanks- seems sensible advice. Much more so than being told to just belt it up to the Rev. limit from the get-go !!!!
     
  8. 16 Aug 2019 at 6:02 PM #8
    zeta4

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    I was advised by CPC just to take it easy for the first 100 miles or so when they did mine.
     
  9. 24 Aug 2019 at 10:00 AM #9
    monkeyboy

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    no running in required when I did mine con rod bearings & mains, garage just said to drop the oil after a few hundred miles.
     
  10. 24 Aug 2019 at 1:03 PM #10
    M3 R0B

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    Same, garage said no need, but I took easy for 500 miles, then drove it normally with some high reving then changed the oil after 1000 miles just to be over cautious. But the oil was clean to be fair so maybe pointless but it doesn't hurt.
     
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  11. 24 Aug 2019 at 3:01 PM #11
    V8mike

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    I took it steady for first 400 miles after the rod bearings got changed. Then i changed the oil about 2000 miles later.
     
  12. 17 Sep 2019 at 8:32 PM #12
    BarsJ92

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    What’s the cost of getting the rod bearings done?
     
  13. 18 Sep 2019 at 3:20 AM #13
    V8mike

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    Including two new engine mounts £1450 but that’s acl bearings not oem bearings.
     
  14. 30 Sep 2019 at 10:28 PM #14
    cossie1

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    Don't rev the tits off it, but drive it normally.

    If you can keep it under 5000rpm for a few miles then great, but don't worry too much if you go over.

    Just drop the oil after 200 miles, so you can check there is no metal in it (which there shouldn't be if you are doing it as precautionary anyway).
     
  15. 1 Oct 2019 at 8:59 AM #15
    Hopz121

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    I just did the RIS procedure again, my Indy said I didn’t need too but for the cost of an oil change it was a no brainer IMO
     
  16. 6 Oct 2019 at 10:13 AM #16
    kully15

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    No need to run them in. Rings need running in not bearings. But wouldn't hurt to take it steady for first 50 miles to ensure all is ok. Then back to 8k of noise :)
     

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