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    M20B30 Stroker build in progress

    Hi Guys,

    I am building a 3.0 liter M20 and I decided to share my experience so far. I would like to note that I am no expert in engine building so if someone has good (or not so good) advice I am opened to opinions.

    The target: M20B30 engine using only (or at least mostly) BMW parts, with least modifications possible. I want to achieve high comp engnine (10.5-11:1) that would be with internals that are as light as possible so that it can rev as high as possible.

    So far the internals I am using are the following:
    M20B25 IX block (I had this one lying arround)
    M54B30 Crank (89.6 stroke)
    M54B30 Conrods (135mm)
    M54B25 Pistons (KH:27.8 - these are the shortest bmw pistons I could find - 0.5mm shorter KH than M54B30 pistons)

    After measuring the deck height it turned out that this one is the tall one, however due to previous overheat the block surface was not flat, so I had to shorten it a bit.
    The result is 206.2 deck height. As a result the above mentioned internals is the pistons sticking 1.5mm over the deck.
    The piston is 6mm thick at its thinnest place (the center), so I figured that it can be shaved with 1mm so that the piston will be only 0.5mm over the deck (since the HG is 1.75mm thick it should be able to handle it without a problem).

    At the first assembly the crank could turn without any issues in the block (crank only)
    I have seen some people mentioning that the oil pump drive needs to be shaved a bit, but in my case there were absolutely no issues. Go figure.
    The first issue was when I assembled one piston and a conrod and connected them to the crank.
    The conrod was hitting the side of the cylinder, it was barely touching it but when the engine is warmed up there will be issues for sure. So here is the solution I cam up with:



    I took off some from the cylinder wall, roughly 2mm in each direction. After measuring with some clay now it has 2mm+ on each side from the conrod to the cylinder wall, so I am happy.

    I had 2 options for the piston modification:
    here they are: (the 2 sides of one test piston)



    This option is the cleaner and better looking in my opinion, the downside is that there are 3mm distance from the top of the piston to the first compression ring so it will transfer alot of heat to the piston rings.

    The alternative design is the following:



    This way there is more metal to the piston ring, however this design turned out to be worse for 2 reasons:
    1 - more sharp edges, and in my case since this will be high compression engine it will be an issue.
    2- the piece of metal at the end of the piston is too near the valve and it might cause a problem at high RPM.

    So bottom line is that I decided to go with the first design for both sides of the piston (intake and exhaust)

    Here is how the piston looks like at TDC:


    One more issue that I faced, is that the spline on the M54 cranshaft is a bit thicker than the M20 one and I had to machine the spocket that holds the timing belt, nothing too major.

    Regarding the head, I am using stock 885 head, with no modifications so far with catcams springs, vac motorsport retainers and reground camshaft to 280 degrees with 10.7 lift
    Nothing interesting there.

    This is my progress so far. I am waiting for the machine shop to do all the pistons so that I can start assembling the bottom end.

    #2
    spline on the crankshaft? what spline are you talking about?

    if you are talking about the gear that drives cambelt then you dodnt need to machine it. just use the oil seal spacer, a longer bolt and different washer and it bolts right up
    Last edited by digger; 12-27-2015, 06:19 PM.
    89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

    new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

    Comment


      #3
      Way cool!

      1986 327i
      transaction feedback
      DIY thing
      meh

      Comment


        #4
        Originally posted by digger View Post
        spline on the crankshaft? what spline are you talking about?

        if you are talking about the gear that drives cambelt then you dodnt need to machine it. just use the oil seal spacer, a longer bolt and different washer and it bolts right up
        I am talking about this little fellow (maybe I used the wrong term)


        It was slightly thicker than the groove on the gear

        Comment


          #5
          you mean the woodruff key? they should be the same size and P/N for the m20 and m54 engines

          shouldnt that gear have threaded holes to hold the vibration damper and crank pulleys?
          89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

          new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

          Comment


            #6
            I dont know, the woodruff key that I removed from the camshaft did not fit into the gear groove, and yes - you are right they should be identical. I have no idea why is there a difference.
            The threads are there, they are just not too visible because of the flash when taking the photo.

            Comment


              #7
              As long as it's a nice snug fit should be ok
              89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

              new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

              Comment


                #8
                A quick update, just got the pistons from the machine shop:






                I am pretty happy with the result. I asked them to leave more material on the lower side, since as per my measurements I had enough space between the valve and piston and decided to leave as much meat as possible on the piston.

                And finally here is the weight of a piston (with the wrist pin and piston rings)
                I am very pleased with the weight.
                All pistons are within 1g difference :)



                I already assembled the crank in the block, and I will put in the pistons and conrods probably tomorrow.

                Comment


                  #9
                  Excited to see how this comes out, I've also thought about putting M54 pistons in an M20 block.

                  1986 327i
                  transaction feedback
                  DIY thing
                  meh

                  Comment


                    #10
                    why are there steps in the top of the piston? is it going need any pockets for the valves?
                    89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                    new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

                    Comment


                      #11
                      keep us updated, looks interesting.
                      http://instagram.com/mundieriss
                      my 88' m20b30 HERE!

                      Comment


                        #12
                        Originally posted by digger View Post
                        why are there steps in the top of the piston? is it going need any pockets for the valves?
                        I wanted to be safe and decided that it would be better to do it like that instead of valve pockets. Also with the current setup (the piston sticking 0.5mm over the deck) and with the lower parts, the CR is 11.3:1 which sounds very good to me for a NA engine.

                        I am going to install the pistons today and hopefully install the head over the weekend and start putting the peripherals.

                        Comment


                          #13
                          Are you using the engine in a 325iX? Perhaps you know this, but... If not, you will have some issues setting up the oil pump. Also, the intermediate shaft turns in the opposite direction on the iX. Dip stick location might be another one too???

                          Comment


                            #14
                            Originally posted by zoomer View Post
                            I wanted to be safe and decided that it would be better to do it like that instead of valve pockets. Also with the current setup (the piston sticking 0.5mm over the deck) and with the lower parts, the CR is 11.3:1 which sounds very good to me for a NA engine.

                            I am going to install the pistons today and hopefully install the head over the weekend and start putting the peripherals.
                            sounds like a pretty high CR with that shape piston. what ECU will you use? you'll need to spend $$$ on a good custom tune as many who have use a flat top design have issues dialing out out the knock as there isnt any squish. id also break any sharp edges on the top of piston
                            Last edited by digger; 01-07-2016, 05:38 PM.
                            89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                            new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

                            Comment


                              #15
                              So without a squish the engine is more proned to knock ? Or nock can't be registered so fast ?
                              Is it because of less turbolence ?

                              I also have same parts here crank and pistons for a future build but the resulting high CR was the problem which i was conserned of.
                              Althoug i have a standalone ecu im not sure if the engine would be to much knock limited. I think it would be an nice engine for E85.

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