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Replacing rod (and possibly main?) bearings

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  • #16
    Originally posted by proctor750 View Post
    "IIRC for rod bearings you want around .0015" give or take a few ten thou.."


    Can anyone confirm these numbers?

    I'm using the plastigage as a Go-NoGo gage so just need to be within spec. I'm a touch under .0015 on cyl 1


    Also- 70t lbs for the ARP seems nuts but I suppose a single torque method must be higher than a multiple torque method to avoid re-torque later. That and ARP's counsel probably suggested the highest allowable number for liability reasons...
    Con rod bearing clearances are here:


    http://m3guru.bmwe30m3.net/s14-rebuild-specs

    If you are at .0015"....you are good...right in the middle of the specs.

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    • #17
      Originally posted by Ironhead View Post

      Con rod bearing clearances are here:


      http://m3guru.bmwe30m3.net/s14-rebuild-specs

      If you are at .0015"....you are good...right in the middle of the specs.
      Yes I remember seeing you post that somewhere else now Thank You.

      "Connecting rod bearing clearance
      Standard classification: 0.0012-0.0027 in. 0.03-0.07 mm
      Double classification: 0.0008-0.0022 in. 0.020-0.055 mm"

      ^^ What's the double classification for? I know they did 3 colors for main bearings and 2 for rod bearings so which is which? Either way I fall into both but just curious which applies to me.


      Also: Doesn't that seem like a pretty large range? No saying it's wrong but it seems like a lot of slop for something like a rod bearing but I'm no machinist.

      Did anyone cringe torquing those poor caps to 70 ft lbs as ARP calls for? ouch

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      • #18
        Originally posted by proctor750 View Post

        Yes I remember seeing you post that somewhere else now Thank You.

        "Connecting rod bearing clearance
        Standard classification: 0.0012-0.0027 in. 0.03-0.07 mm
        Double classification: 0.0008-0.0022 in. 0.020-0.055 mm"

        ^^ What's the double classification for? I know they did 3 colors for main bearings and 2 for rod bearings so which is which? Either way I fall into both but just curious which applies to me.


        Also: Doesn't that seem like a pretty large range? No saying it's wrong but it seems like a lot of slop for something like a rod bearing but I'm no machinist.

        Did anyone cringe torquing those poor caps to 70 ft lbs as ARP calls for? ouch
        I DO NOT understand the "Standard Classification-Double Classification" crap BMW uses....but you are well within either spec range. If it makes you feel better...I have done the bottom end assembly on two engines...and each time wound up with right around .0015" rod bearing clearance.

        And those are the BMW specs....I don't really think the range is "pretty large". Keep in mind the difference between the low and high range is just a bit more than a thousandth of an inch....well less than the thickness of a human hair.

        I used ARP rod bolts...but with Pauter rods. I tightened them with a stretch gauge...and IIRC the correct stretch was obtained at about 55 ft lbs....but if you are using ARP bolts with standard rods I have no doubt the values are different. Bottom line....do what ARP says....and make sure you use the exact lube they specify....and make sure the threads are clean. They made the bolts and know what they are talking about.
        Last edited by Ironhead; 03-30-2018, 11:41 AM.

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