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e30 M3 minor rust repair.

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    The next set of measurements are for "taper". Three measurements are taken across
    the journal at the same angle and your comparing the centre measurement to the ones
    either side of it. If the journal is "straight" then the centre will be the same as both the outside
    measurments (D = C and E on the left in the diagram below).
    However if the outside measurements are less than the middle one, like on the right of the diagram below,
    then wear has caused the journal to become tapered. Again there's a tolerance for how far things can
    go before they require machine works, and again I'm using a tolerance of 0.0004".

    Thankfully this crank measured up ok, and all reading from both the 5 main journals
    and the 4 conrod journals were within tolerances, so there was no needed to have
    any of the journals reground.
    The other thing which we could now tell by looking at all the measurements just taken
    was that this crank had never been reground before. How can we tell this? Well by looking
    up the tolerance manual we could see the various sizes for each step

    original main bearing size from factory = 2.1649" to 2.1644"
    1st undersize (reground by 0.010") = 2.1551" to 2.1544"
    2nd undersize (reground by 0.020") = 2.1453" to 2.1445"
    3rd undersize (reground by 0.030") = 2.1354" to 2.1347"

    As all my main journals came in around 2.1649" we could surmise that they were still
    original an had never been ground down to have wear repaired. And it was the same case
    with the conrod journals........

    original conrod journal sizes from the factory = 1.8894" to 1.8888"
    1st undersize (reground by 0.010") = 1.8796" to 1.8789"
    2nd undersize (reground by 0.020") = 1.8697" to 1.8691"
    3rd undersize (reground by 0.030") = 1.8599" to 1.8592"

    All my conrod journals came in around 1.8894" so again using the figures above
    we could tell they hadn't been touched.

    So, why the hell do I need to know all this crap? Well, in a little while we're
    going to get into choosing bearings for each of these journals, and, just like the
    the journals can be ground to 3 smaller sizes to repair wear, the bearings can be purchased
    in three undersizes aswell as standard to match the size of the journals.
    Your going to need to know the size of the journals so you can buy the right bearings.

    As you've seen above none of the journals on this crank required grinding down to correct them,
    however, she did still pay a visit to the machine shop and that was to have each journal
    micro-polished to get the journals as absolutely smooth as they can be gotten.
    Not an essential step but it helps keep the O.C.D. at bay.

    The only other thing worth mentioning before moving on, is if your crank should happen
    to be outside any of the wear tolerances or is showing signs of pitting or scratching etc.
    then your machine shop should be aware of these undersizes and will choose what size to grind
    it to, to return it to a smooth surface and still ensure that you can buy bearings that will fit
    the new size. But, one word of warning, upon return of your crank from the machine shop
    YOU'VE got to measure it to verify the sizes. The more you rely on other people to take
    important measurements the greater the risk of a fuck up, which YOU will most likely
    end up footing the bill for.

    Next item to address on the crank was the surface that the rear oil seal runs on.
    Strange as it may sound, after 170 odd thousand miles the lip of the oil seal has actually worn
    a deep ridge into the hardened metal of the crankshaft.........

    A worn ridge like this is actually fairly common on a high mileage crank and
    while we can't repair it, it doesn't pose to big a problem, we'll simply ensure on
    reassembly that the rear crank oil seal is refitted a few mm either side of this ridge
    so it can seal against a fresh non worn piece of the surface. With that in mind, the rest of the
    surface could do with a little clean up.
    A few strips of wet and dry sand paper starting off at 600 grit and working up
    to 1000grit with the aid of some light oil soon polishes up the rest of the surface.....

    Last edited by xworks; 04-18-2011, 09:01 AM.


      Switching to the front end of the crank next, and it's the crankshaft timing chain
      gear's turn for some attention. Below you can see a pic of the gear. There's three
      rows of teeth cut into the gear, the front two to drive the timing chain and the
      rear one to drive the oil pump chain.......

      With the mileage on this engine almost all the timing chain parts are showing
      signs of age and while this bottom gear isn't actually too badly worn, new timing
      chains have a nasty habit of sounding noisy when fitted onto old gears.
      So stretching the mastercard to levels of debit normally associated with third
      world countries run by shady dictators, we're going to change all the timing chain
      components on this build. With that in mind the gear needs to be removed.......

      she was a tight bugger, but, with the help of a hydraulic pullers and some foul
      language she didn't stand a chance......

      With the gear off you could get a better look at the wear on it.
      I say "could" because if you were standing here holding it in your hand you
      "could" see it perfectly, but, with this poxy Fisher Price camera you'd be lucky to
      tell if all the teeth were still intact.......

      fear not,
      using the cutting edge technology of the "Microsoft Paint Microscope"
      we can zoom in to "never before seen" levels of detail.......

      What you s******ing at? This shit here cost mucho dollar.

      What your looking at above is how a timing gear typically gets worn. The valley
      between the two teeth gets worn down over time (red shaded area) and the tips of the
      teeth become "hooked" as a result (red arrows). All this leads to a harder life for the
      chain, as the nice round link on the chain now has a sloppy valley to ride in which allows it
      to move around more, wearing the link and the valley more as it does so. The only slight
      upside though, is that almost always, the increasingly loud noise a worn chain and gears will
      make give you some sort of advance warning that all is not well, as opposed to a timing belt
      which just makes expensive noises right after it breaks.

      Anyway with the gear removed the shaft gets a lick of fine emery paper to clean it up before
      the new gear is refitted........

      The new gear is an interference fit onto the shaft (thats a fancy way for
      saying you need to hammer the shit out of it to get it on). To help in this process
      the gear is first heated up, the correct temperature is reached when you pick
      up the gear, smell burning, and then pass out with the pain.......

      real men mange to fit the gear before passing out........


        Final item up for attention on the crank is the spigot bearing fitted into the
        rear of the shaft........

        Borrowing a picture from long, long, ago you may remember the input shaft
        on the gearbox shown below. Well as you can see this shaft is supported on one
        end by a bearing in the gearbox casing, it also needs to be supported the other
        end (red arrow) and this is taken care of by the spigot bearing in the end of the crank.......

        Since every other bearing has been changed during this rebuild, Murphys Law states
        that should I choose to reuse this one, it will most likely fail as soon as I drive out
        the garage door and result in the car exploding, or something.
        So, how to remove it? Well, you could use an appropriate sized internal pullers
        to get the little bugger out, or, you could use the tight arse method.

        A socket large enough for the bearing to fit inside, a couple of washers, a
        long m6 bolt, two m6 nuts, an m6 Rawl bolt and a partridge in a pear tree.......

        assembled as follows, bolt, one nut, washers to prevent bolt passing into socket
        and socket itself.......

        another nut the opposite side of the socket..........

        and finally the Rawl bolt.........

        the deal is we're going to pop the end of the Rawl bolt through the centre of the
        spigot bearing and tighten down the first nut onto it, to spread the legs of the
        bolt behind it like so........

        then with the socket placed firmly up against the crank the second nut is tightened down
        against the washers which pulls the bolt outwards along with the Rawl plug.......

        and hopefully the spigot bearing to.......

        if it doesn't, then go out and buy the proper tool and stop being a tight arse.
        With the bearing out, the hole where it came from is given a quick clean......

        before a new bearing is refitted......

        using a socket thats the same size as the bearing outer race and will drive
        it down into the hole all the way home.......

        a wee dab of grease goes in to keep the bearing happy.......

        and then finally the rest of the washers and stuff follow the bearing into
        the hole in the order shown below to complete the job......

        With the crank good to go, next up will be the task of choosing the correct
        sized bearings.

        Which we'll get to later this week, till then..................


          I want to have your babies


            Once happy with the crank we could move on to sizing and ordering the correct
            bearings. First up was a quick check that all the bearing journals in the block were
            straight and fit for purpose. Just like checking the top face of the block for flatness
            this check is much the same. Block is upturned on the stand.........

            and the flat edge is placed across the journals, and again check to see if you
            can squeeze a 1 thou feeler blade between the flat edge and any of the journals
            which would show they are out of line. It's unusual to find these out of line and if they
            are it's usually because the block has taken a fairly extreme overheating causing
            the block to warp or the engine is being rebuilt due to a "catastrophic engine failure"......

            Once this check is done each of the main bearing cap's are bolted down and
            torqued, one at a time..........

            where upon the bore gauge is used again to measure the internal size of the
            block journal. It's measured at a couple of different angles to make sure the
            journal is perfectly round........

            Once the above check is complete and none of the journals show an
            ovality (out of round) of more than 0.0004" we're ready to start figuring
            out what size bearings we're going to need to house the crankshaft when fitted
            back into the block.......


              Now for the next bit I've gone a bit mad with the crayons again, and as usual
              with these diagrams your going to have to use a fair dose of your own imagination
              to make any sense out of this, but we'll give it a try.

              Below is a picture of that block main journal and cap that we just measured. The
              green bits just inside it are the bearings we're going to be fitting in a minute, and
              the grey circle in the middle is the crankshaft when it's fitted........

              What we're interested in is the red bit. Thats the space between the crankshaft
              and the crankshaft bearings. Its into this "gap" that the engine oil pump pumps oil
              while the engine is running. The reason it pumps oil in here is that we don't actually
              want the spinning crank to touch the bearings while the engine is running, we want
              a nice protective barrier of oil between the crank and the bearings.
              And if we pump in just the right amount of oil, under the right pressure and choose
              the right sized bearings so that the gap the oil has to fill is just right, the crankshaft
              should spin perfectly inside it's little thin "cushion" of oil and never actually touch the

              The reason we need that gap (oil clearance) just right, is, if the oil cushion should
              happen to break down and the spinning crank should happen to make dry contact
              with the surface of the bearing then things can turn nasty very, very, quickly.
              Bearings can get chewed up in the blink of an eye.........

              and the nice smooth crank journals they were protecting usually don't escape either..........

              (both pictures courtesy of Google)

              So by this stage you've probably got the idea, that gap between the crank journal
              and the bearings known as the "oil clearance" has got to be just the right thickness.
              To get this gap correct we choose the exact right sized bearings.

              Now we already know from measuring the crank journals earlier that the
              crank hasn't been ground down, so, this get's us in the ball park with bearing
              selection. We need standard sized bearings, however we're not finished
              yet. All 4 size's of crank bearing (standard, 1st, 2nd and 3rd oversize) come
              in two flavours, red or blue. A red bearing is very, very slightly thicker than a
              blue bearing and it's the choice of these two slightly different sized bearings that
              lets us fine tune the oil clearance gap.

              So, how do we do this? Is this going to take long? I've got stuff to do can we speed this
              along please?
              Patience, we're nearly there.

              We're going to take number 4 crank bearing journal as an example. Earlier we measured this journals
              diameter at 2.1650". By searching through the Tolerance manual we find that the tolerance for the oil clearance
              gap is 0.0008" to 0.0027". I'm shooting for a gap of 0.0020" on this build, so if we take the crank journal diameter
              of 2.1650" and add the target oil clearance gap of 0.0020" to that, we get 2.1670".
              So, when we fit a pair of bearings to the block, like shown below, we want to measure the hole
              at 2.1670".........

              We start off by fitting two red bearings and measuring the gap with the bore gauge.
              What we find is a vertical measurement of 2.1668" which would give us an oil clearance
              of 0.0018" (2.1668" minus journal diameter of 2.1650").
              It's close to the target of 0.0020", but, not close enough.
              So, we fit two blue bearings and again measure the diameter of the hole. This
              time we get 2.1674", which would give us an oil clearance of 0.0024".
              Again close but just a little to big.
              So the final attempt, we fit one red bearing and one blue bearing, and again, stick the bore gauge
              in to measure the hole. What we got was 2.1671".
              An oil clearance of 0.0021" which is more or less bang on the target of 0.0020".
              We now know that number 4 crank journal needs 1 blue and 1 red bearing for the
              correct clearance.

              Unfortunately, this whole procedure has to be repeated for each of the remaining 4 journals
              to obtain the right sized bearings for each one.

              And there's another down side, the surface of the bearings have a very fragile surface coating known
              as the "babbitt" surface. And a negative side effect of using the bore gauge to measure the bearing
              diameters is that the tips of the gauge damages this coating..........

              For this reason, we use a set of bearings just for measuring purposes......

              When all the measuring was finished and the quantity of blue and red bearings
              needed were known the order was placed.....


                With the new bearings shells in hand we could complete the final checks and measurments.
                Of the 5 pairs of main bearings bought, 4 are identical in shape, however
                1 pair are slightly different than the rest and these are fitted to journal number 3.......

                The difference with this pair is the bearing shells have "shoulders" on them
                for want of a better description. As you can see below, along with the main
                bearing surface in the valley to support the crank, these also have an extra
                bearing surface around the sides as well.......

                The reason for this is these pair of bearings known as the thrust bearings do two jobs.
                The first is just like the other bearings and thats to support the spinning crank, but
                the second job is to limit the crank from moving left and right in the block.
                And they do this by pushing against the "thrust faces" machined into the crank
                either side of number 3 journal..........

                when the crank is sitting in place these "shoulders" on the bearing keep the
                crank snugly located. As you may expect when the crank is in place these shoulders
                don't rub up tight against the crank, as if they did, after a short while spinning at a couple
                of thousand revs the crank would have them worn down. Instead the Tolerance manual
                gives us a minimum and maximum the gap should be between the bearing side face (thrust face)
                and the crank(arrowed red below)..........

                To measure this gap the bearing cap and it's thrust bearing are fitted
                along with the thrust bearing below it in the block......

                Before the cap bolts are torqued down the crank is given a few soft taps left
                and right to get the two thrust bearings perfectly in line with each other........

                and then a dial gauge is strapped to the end of the block with the needle resting
                against the crank.......

                then a flat screw driver is used to GENTLY prise the crank left and right in the
                block and the dial gauge at the end will show how much the crank is allowed to

                The figure it's allowed to move is know as "Crankshaft End Float"
                and the Tolerance Manual states that it's got to be between 0.0033" and 0.0068".
                Mine was 0.0041" so we're good to go.


                  For the next test the crank is again removed and all but the outer two of the bearings
                  in the block are removed too.......

                  (for all these tests where the crank is fitted with the bearings you should
                  give a little smear of oil to the bearings by the way, never a good idea to lie
                  a crank in dry on top of bearings. Just a little dab of oil will do, your not looking
                  to recreate the Exxon Valdez disaster )

                  the crank is then sat back in resting on these two remaining bearings.......

                  and a dial gauge is set up so that the needle is resting on number 3 bearing journal
                  smack bang in the middle of the crank like so..........

                  What we're checking for here, is to see if the crank is perfectly straight, or, if it
                  has any "wobble" in it, know as "run out". The crank is rotated and a close eye
                  kept on the dial gauge to see if the centre journal is moving up or down showing
                  that the crank isn't perfectly straight. The factory tolerance for Run Out is a maximum of
                  0.0040", I'd prefere to see less than 0.0020" personally, but either way, mine had no
                  perceptible movement at all, which either means the crank is perfectly
                  straight or I fu*ked up the test. I choose to believe the former.

                  And then finally on to the last test, and it's a check just to confirm the oil clearance we
                  worked out a while ago between each bearing and the crank. For this test all the bearings
                  are assembled into the block and caps, ensuring all the red and blue sized bearings go where
                  they're supposed to go........

                  and then we take out the plasitgauge.......

                  Plastigauge is basically little thin strips of plasticine. You can see the little strips
                  above (red arrow). You cut off a little piece of these strips place it between
                  the bearing and the crank, torque the bearing cap down and then remove the
                  cap again. What should be left behind is the little strip of plasticine, which has now been
                  crushed flat. And thanks to the precise nature of this stuff you can use the guide card
                  shown above (green arrow) to measure how squashed flat the plasticine has become
                  to figure out how much of a gap you have.
                  The bigger the gap the less it will have been crushed, the smaller the gap the flatter it will be.
                  I make it sound complicated.
                  It's easier just to show you. Cut a little piece of the Plastigauge...........

                  Place it onto each of the crank bearings........

                  bolt down all the bearing caps and torque them up........

                  and then remove each cap to reveal the squashed Plastigauge........

                  and then finally using the little measuring card you can match up how squashed
                  the Plastigauge is to the correct marker on the card, which will tell you how much
                  oil clearance you had when the cap was bolted down.
                  If you remember earlier the target was 0.0020", and you can see below that the
                  card reads exactly 2.0, which is 0.0020".

                  tickety fu*king boo.
                  More as the week goes on, if this hasn't already made you loose the will to live......


                    Originally posted by xworks View Post
                    More as the week goes on, if this hasn't already made you loose the will to live......
                    Quite the opposite. I want to get a few of my own Mastercards and build an M3
                    Originally posted by george graves
                    If people keep quoting me in their sig, I'm going to burn this motherfucker down.


                      With the crank main bearings all done and dusted, all that remained was to select
                      the conrod bearings. First up was to check the conrods themselves. These take
                      a fair pounding in the engine and it's not unusual to find wear here, so, it's out with the
                      bore gauge again and both the big ends and the small ends get checked for roundness and wear......

                      The big ends on my rods came up just about ok, but, unfortunately the small ends were
                      showings signs of a lot of wear. Below you can see a closer picture of the small

                      What you can see above is that the small end bore actually has a bronze bush inserted into it
                      to increase it's wear resistance. But, theres only so much a bush can do, twenty years of constantly
                      trying to hold on to a piston takes it's toll. A quick look up of the tolerance manual tells us this bush should
                      have a diameter of 0.8669" to 0.8671". Before even measuring mine I could tell they were fairly worn.
                      If you placed a gudgeon pin into any of the rods you could actually feel it rock a little in the bushing.........

                      And this was backed up by the measurements, all four small end bushes were well
                      over the 0.8671" size, with the worst coming in at 0.8682".
                      So, options?
                      Well, you can have the bushes replaced by a good machine shop, but, it's a pricey
                      exercise around here and who ever does it really needs to know what they're at as
                      it's fairly easy to make a balls of it. Plus one of the rods big ends was also just on the border
                      of being "out of round".
                      Option number two was carry out an armed robbery on the local main dealer to
                      get some new rods, not a great option really, the rods have a 5 day delivery time and
                      there was a good chance a member of staff would press the panic button while we all waited
                      for the rods to arrive.
                      Which brought us to option number 3, aftermarket rods.........

                      The new rods are forged in a "H" beam design, and they've
                      also been shot peened, crack tested and balanced end to end, all of which means
                      they should be a good bit stronger than the originals. Which in turn means you should be
                      able to raise the rev limit of the engine without the fear of one of them popping out through
                      the block to say hello.
                      With the state of tune this engine is being built to I won't need to raise the rev limit much
                      to achieve the engine's maximum horse power, so all they need to be for this build is equally
                      as strong as the originals and not require you to sell a kidney to obtain them, like the originals would.
                      Another nice benefit of the new rods is that they're lighter than the originals, to the tune of
                      51 gram's per rod..........

                      Which helps with the other objective of this build, and thats where ever possible
                      to lower the weight of the rotating mass of the engine. Simply put, trying to make
                      anything that moves in the engine lighter with objective of having an engine thats quicker
                      to rev.
                      As with most after market rods these ones also came with ARP rod bolts, which are stronger
                      than the originals. I would have been perfectly happy to use a new set of original bolts, as to the
                      best of my knowledge they are a good design rod bolt to begin with, but the new rods are tapped out
                      for the threads on the ARP bolts, which is different to the original bolts so thats what we'll be using........

                      Like the original bolts the ARP one's are also stretch bolts. Basically when you tighten them down
                      the bolts stretches a little and it's this stretch which keeps the bolt tight over time. When a stretch bolt
                      is undone sometimes it returns to it's original length and in this case it's usually good to go again. However
                      sometimes it's doesn't, it stays a little stretched when loosened and when this happens the bolt can't be
                      guaranteed to stay tight if it's reused again. For this reason standard rod bolts are always changed when doing
                      a rebuild because you've no way of telling whether they've returned to their original lengths when removed.

                      However, with the ARP bolts you can measure the exact length of a new bolt using the proper tool and if you
                      record this length and the bolts fitted position you can now tell if it's fit to be reused next time around..........

                      The down side is the extra effort required to do all this is a pain in the arse if you are inherantly

                      New rods get the once over with the bore gauge to make sure they're exactly what was paid for.......

                      After which we move on to sizing the conrod bearings.
                      Now unlike the main bearings where you had the choice of a red or blue size bearing
                      to fine tune the oil clearance gap, with the conrod bearings BMW have decided to make
                      the choice a lot simpler. You can have yellow, yellow or yellow.
                      Yep, theres only one thickness conrod bearing available from the main dealer and thats
                      If the conrod journals on your crank have been machined down to 1st, 2nd or 3rd undersize
                      to correct wear then you still have a choice of 1st, 2nd or 3rd oversize bearings to match this,
                      but thats as far as the decision making needs to go.
                      That doesn't however mean that you'd don't need to check the clearance, that'd be far to simple.
                      So, pair of yellow bearings in and the conrod cap torqued down, out with the bore gauge and measure
                      the diameter..............

                      Diameter measured at 1.8913", quick check of the notes to see what the matching conrod
                      journal on the crank was, and it shows as 1.8893". Take one from the other 1.8913"-1.8893"
                      and your left with a conrod big end oil gap of 0.0020".
                      Tolerance manual says between 0.0008" and 0.0022" is good to go.
                      As usual, each individual rod is measured to figure out it's clearance and then later verifyed
                      with the Plastigauge.

                      Just a quick one on the bearing colors before we leave it, if you've never seen a BMW bearing before
                      the colours (blue and red for the mains and yellow for the conrods) are actually marked on the edge
                      of the bearing shell. You can just about see the little yellow smear on the conrod top bearing below at
                      the 12 o'clock position...........

                      And that takes care of all the prep work for the bottom end for now,
                      next up we'll be moving on to the cylinder head.
                      Using match sticks to keep your eyes open yet?
                      Last edited by xworks; 04-21-2011, 02:35 PM.


                        not to smuge an otherwise flawless build, but:
                        The new rods are forged as opposed to the originals which were cast,
                        with very, very few exceptions, *all* rods are forged. Even POS 3 cylinder Geo Metro rods. They just wouldn't hold up otherwise. Certainly all BMW rods are. However the H beam rods you've chosen can be stronger while using less material, making them lighter, even though they are both forged. Can't go wrong there.

                        please, carry on..
                        Build thread



                've spotted my.....em......deliberate
                          trap to see if people were paying attention.
                          Thank you for the correction :up:
                          I've edited the original post in an effort to deal with
                          the shame. ;)


                            I'm saving this thread to build engines by in the future.


                              seriously though, I'll be coming back to this thread when I build my next engine :D

                              any thoughts on end balancing the rods?
                              Build thread



                                Originally posted by nando View Post
                                any thoughts on end balancing the rods?
                                Thankfully these rods came already pre-balanced which was handy as
                                I didn't like the idea of having to grind them after they had been shot peened.
                                A local machine shop has balanced my rods for me in the past as a
                                decent rig for weighing them end to end is still unfortunately way down the
                                list of things I need to buy.
                                Some day.
                                For anyone that mightn't be familiar with the process of balancing rods end to end
                                this video more or less lays it out..........