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    #1

    Engine Refresh Opinions

    I'm refreshing the e motor out of my e30 to swap in my e28. With over 350k she is well below 100psi on three cylinders. The motor I'm building was gone through a while back but the back 2 cylinders were down and a leak down test showed I had a burnt exhaust valve and leak down past the rings.

    So basically I'm looking to refresh this one on a budget. I have all the mics and measuring tools to check the cylinders and crank.

    I'm thinking of measuring the crank and cylinders and if everything is still in spec just clean it all real good, hitting the cylinders with a ball hone (sp?) since the cross hatching is still visible and putting if all back together with new rings and bearings.

    Think I'm building a ticking time bomb?


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    #2
    I know that the e bottom end is pretty durable. I've seen ones with 500k on them.

    I'm not saying you shouldn't rebuild it or anything but if you are only going to keep this car for a few more years I would buy a 885 cyl head and put it on with a new gaskets and drive it.
    M30 is God's motor.....but Jesus drives an M60'd car -slammin.e28

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      #3
      You won't be building a time bomb if you build the engine the right way. That means making sure that wear parts (cylinders, journals, etc) are still within spec as measured to a the thousandth. If the cylinders are okay, refreshing the cross-hatch and new rings will work. I highly recommend having the crank journals polished. Then pick the rod and main bearings by "color" to match the journal dimensions. Check the wear on the intermediate shaft bearings as if they are worn oil pressure will suffer. Use a new oil pressure pump and regulator valve.

      Have a minimal (~0.005") surfacing cut done on the head.
      The car makes it possible, but the driver makes it happen.
      Jim Levie, Huntsville, AL

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        #4
        I just measured everything and it looks like I'm all within spec for standard rings and bearings. Now its time to spend the money and check my clearances with plastigauge and ring gaps.

        At work on air cooled Kohler engines we deglazed the cylinders with 400 grit sand paper by hand if there is no cylinder wear with no problems. You think this is a good method or should a get a ball hone?


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          #5
          Originally posted by LavaSurfer View Post
          I just measured everything and it looks like I'm all within spec for standard rings and bearings. Now its time to spend the money and check my clearances with plastigauge and ring gaps.
          Plastigauge is good for making sure you haven't made a grievous error, but not much else. Bearing clearance is made correct by measurement of the journal to a tenth and then using the correct "color" bearing to get the right clearance. If you are lucky, a single "color" of main bearings and a single "color" or rod bearing will work. But it isn't unusual to have to use bearings from more than one set.
          At work on air cooled Kohler engines we deglazed the cylinders with 400 grit sand paper by hand if there is no cylinder wear with no problems. You think this is a good method or should a get a ball hone?
          Most of the time, the wear in BMW cylinders will be towards the bottom. The cross hatching may be still visible at the top when the lower parts of the cylinders are worn out of spec. Checking for wear means three lines of measurement 120deg apart at three point along the bore, with a dial indicator that reads to a tenth. Is that what you did?

          Simply removing any glaze with 400grit isn't sufficient (even for a Kohler). A proper cross-hatch is necessary to hold the oil that is needed to get the rings to seat. The angle between the cross-hatch lines is important. This is a jobe best done by a cross-hatch machine, though I know a couple of machinists that can do it by hand and wind with results that can't be distinguished from a machine job. But those guys are pretty rare.
          The car makes it possible, but the driver makes it happen.
          Jim Levie, Huntsville, AL

          Comment

            #6
            You should probably also check the pistons for clearance with the bore and proper ring groove clearance.
            A ball hone will make it much easier to get a good bore finish. I don't see how you could get the angle right with sandpaper.

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              #7
              I just ordered a ball hone. We never take much off with the sandpaper at work....mainly just deglaze the cylinders without disturbing the factory cross hatch pattern. The main reason we re-ring motors at work is if the customer neglects cleaning the air shrouds and over heats the engine. If they don't continue the run the motor for a long period of time the cylinders are still in good shape and the rings just lose their temper....hence just a quick scuff and ring job...

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