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Replacing rod (and possibly main?) bearings

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  • Replacing rod (and possibly main?) bearings

    Hi all,
    I have the S14 out of the car and on a stand for a mild refresh.
    The engine has around 120K miles on it and has been well cared for.
    In the last 8,000 miles, the previous owner had around $3,000 of work done to it. Head gasket, timing chain rails, chain tensioner, water pump and some other things.
    I've searched the various threads on rod bearing replacement but a few things are still unclear, or I'd like to confirm.

    1. What is the torque spec for the OEM rod bolts?
    2. Assembly lube on both sides of the bearings, or only the side facing the crank?
    3. What is the clearance range for the bearings?

    This seems fairly straightforward:
    1. Remove end cap.
    2. Push piston up a bit to allow rod side bearing to be removed.
    3. Install new rod bearings.
    4. Using the old rod bolts, torque to spec with Plastigauge to confirm sizing.
    5. If sizing is ok, lube bearings with assembly lube (both sides?), reassemble and torque with new rod bolts.

    The mains seems a little more controversial. With the engine out of the car, it does seem like it would be easy to simply tap the old bearing shells out from under the crank, and tap new ones in. There's many videos on Youtube of people doing that on various cars, and it seems to go smoothly.

    The issues I see with that are:

    1. It seems like there were many different sized bearing shells used in the assembly of each engine, presumably to "fine tune" the gap to a very narrow range. Yet, places like FCP sell main bearing kits that are just "standard" size. So that seems inconsistent. Will the bearings in the car have color codes that I can still see? If that's the case, should I check those and order that same color scheme? Not sure on that.

    2. Can the main bearing bolts be reused? (I know the rods can't, but the answer on the mains seems unclear).

    3. Is tapping the mains out from under the crank really as easy as it looks??

    Thanks very much!

  • #2


    • #3
      Or is this correct?
      55 nm is around 40 ft lbs.


      • #4
        I will try to answer some of this....

        The specs you listed for torque "seem" about right....if you got them from a reputable place I'm sure they are. You understanding the final tightening is by angle, rather than torque, right? I always have replaced the stock bolts with ARP which come with a simple torque spec, so angle torquing is not needed.

        Main bearing bolts can be reused, connecting rod bolts should never be (unless you use aftermarket like ARP).

        Some disagree with me....but I think trying to swap rod/main bearings with the engine in the car is a bad idea. Pulling the engine is not "that" complex....why not just do it the right way? To swap main bearings, you would have to pull the tranny/bellhousing, the clutch/flywheel, RMS carrier, the crank pulley, the timing chain cover....and probably a lot of other things I am makes no sense. I wonder if the people who recommend that plan have actually ever done it....?

        It is possible to replace the rod bearings with the engine in the car....but you will still have to do a lot of work on your back under the car while oil drips on your face (once you pull the oil pan, oil will drip for days), and trying to do precision/critical work like replacing rod bearings and checking clearances under these circumstances.....I dunno. Sounds like a bad idea to me.

        As far as bearing will have to track down the specs I don't have them in front of me. IIRC for rod bearings you want around .0015" give or take a few ten thou.....and main bearings around .0025" with the same tolerances. The difference between the red and blue bearings is simply that one of them (don't remember which is which) gives a few ten thou clearance more than the others. To get clearances consistent and within tolerance you might have to use some red and some blue....that seems to be how it often shakes out.

        To expand on what I said above....I think "tapping the main bearings out from under the crank" is a really bad idea. I presume that would involve tapping the new ones in, and they are super soft....almost like lead. You would be certain to damage them.

        Again, sometimes doing things "right" pulling the not only better but at the end of the day also easier....

        Last edited by Ironhead; 02-01-2017, 12:26 PM.


        • #5

          Sorry for my long first post, stuff gets lost in it.

          But as I said, the engine is out of the car and on the stand. Stripped to the long block at this point.

          As far as torque for the rod bolts, I found conflicting info. In my Post 2 above, it says do it in stages - 7 ft lbs, then 22 ft lbs, then 60 degrees.

          In my Post 3 above (which also appears to be from a manual), it says torque to 55 nm (40 ft lbs). Not in stages, just straight to 55 nm.

          My guess is they end up being close to the same torque, but I'm not sure.

          As oil clearance for the rod bearings, what I've seen is - Big end oil clearance = 0.0009” – 0.0025” (0.0024mm – 0.064mm). I'd like to confirm that.


          • #6
            Here is a link with a bunch of stats that you will find useful. I have found them all to be correct:


            Just ignore the "triple bearing classification" part.

            Sorry...for some reason I thought you were trying to do this with the engine in the car...apologies for not reading short attention span at work.

            I don't understand then the part about "tapping" the main bearings out. Once you remove the crank you should be able to pull out the main bearings with your fingers. The are kind of wedged in, but not very tightly. Same with the rod bearings.

            Regarding the discrepancy in rod bolt torque figures....I think you are would make sense that the two methods would result in about the same preload.


            • #7
              As far as tapping in the bearings, see this video (you can start at 2:30)



              • #8
                Hi I would just like to add to Ironhead's good advice, with regards to bearing colours do yourself a favour as the best starting point buy BMW genuine set of Red big end bearing shells
                install them and palsti-gauge to target 0.0015-0.002” may have to buy and use some Blue shells as well.

                If you are going to do the main bearings I can not see any issue with following the tube video but would remove all the main caps at once that way the crank is only resting on the shells in the block and they can be monovered out and replaced one at a time with the aid of a credit card cut in strips to push the shell out bearing in mind that the crank won’t rotate due the timing chain is attached.

                Red main shells in the block and buy and try Blue in the main caps I think that would suit a used engine

                E30 M3 1987
                Mini Clubman GT
                BMW E36 323 Msport
                Toyota Corona
                KTM 200EXC
                Honda CB50 (1979)


                • #9
                  Originally posted by SoCalE30M3 View Post
                  As far as tapping in the bearings, see this video (you can start at 2:30)

                  The only reason I can see to do that would be if you did not want to remove the crank....why not just remove the crank....?

                  You will need the crank out to check clearances anyway....although I did not watch the entire video....short attention span again...


                  • #10
                    I've got a full set of Blue Evo bearing shells that I didn't use for my rebuild, WPC coated if you were interested. I bought both red and blue and ended up only needing the red.

                    1988 M3
                    2007 Lotus Exige S


                    • #11
                      Thanks for the offer, but I already have a set of ($400, ouch!) factory BMW standard shells to use.


                      • #12
                        Late to the party here. There are 2 different posted specifications for the connecting rod bolt torque. There is the later version listed in BMW TIS, which is graciously hosted by bmw guru here:

                        If you click the torque specs on the right side of the page, then scroll down to 11-24 connecting rods and bearings. The newer spec given is 55Nm. Curiously the spec for the S38 connecting rod bolts are the older of: 5Nm, then 30 Nm and a 60° stretch. Both connecting rods are identical, as long as the weight class is the same.

                        I still have the old spiral notebook, which lists the older specification of the three step method for the S38 (above) for BOTH connecting rod variants. We have been doing them this way since 1988. My thinking is thus: The older method is better as the final torque (of the newer method) can vary dependent on what lubricant is used on the threads. WD-40 to ARP rod bolt lube as an example. The ARP lube is very slippery and will result in a higher torque value applied to the bolt vs: that of a thin oil like the WD-40.

                        Angle is more consistent and you end up with a better loading of the fastener. W/O the variables of which lubricant was chosen for the newer method.

                        Rod bolts are a ONE TIME use.

                        Don Fields


                        • #13
                          Hi Don,
                          Small world, you were kind enough to take some of your time to speak with me on the phone a few weeks ago regarding the torque issues.
                          I'm done, the engine is back in the car and runs beautifully. Thanks for your help, and thanks everyone else for your help too!


                          • #14
                            Originally posted by Ironhead View Post

                            It is possible to replace the rod bearings with the engine in the car..on a race weekend in the rain in the paddock between qualifying and the race..but you will still have to do a lot of work on your back under the car while oil drips on your face (once you pull the oil pan, oil will drip for days), and trying to do precision/critical work like replacing rod bearings and checking clearances under these circumstances.....I dunno. Sounds like a bad idea to me.

                            Fixed it for you. :-/ Yep.

                            To add to what others have said

                            just replace the rod bolts with ARP
                            use coated bearings
                            you can do it in with the car on a lift if you know what you are doing
                            drill an extra hole in the center of the bearings for better oil flow
                            2010 BMW Club Racing E30 M3 Touring Car Champion
                            2011, 2013 SCCA Runoffs Super Touring Under 3.0L Bronze Medalist
                            2011 SCCA Jim Fitzgerald Rookie of the Year
                            2012 SCCA Northeast Divisional STU Champion
                            2015 SCCA Runoffs STU Polesitter


                            • #15
                              "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 gauge so just need to be within spec. I'm a touch under .0015 on cyl 1

                              Click image for larger version  Name:	0015.png Views:	1 Size:	258.2 KB ID:	1269293Click image for larger version  Name:	0015 2.png Views:	1 Size:	409.5 KB ID:	1269294

                              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...