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Hydrolocked field find rebuild help

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    #1

    Hydrolocked field find rebuild help

    Found an 88 325i in a field for $300 PO said they drive it through low water and hydrolocked it. I pulled the head and pan and found 2 bent rods. I would like to
    A) drive the car reasonably soon cause I miss my old e30 very
    B) not spend a fortune on performance parts but not waste a good opportunity to upgrade a few things "while I'm in there"

    I do have an old M50TU short block that I has the same stroke as the M20 of 75mm
    I couldn't find definitive information on these rods being a direct swap so I cleaned one up and threw it in to see


    As you can see the deck height is different I stick up about 3mm above the deck. I do know that these rods are 140mm long but they also sit higher up into their mating Pistons. I have read that the m20 engine can benefit greatly from a wee bit longer rod (as per metric mechanic) the M50 piston is significantly shorter too which I read is also a bonus for revving. And last it has oil holes drilled in and around the oil scraper ring for cooling and reduced oil consumption (I assume)

    My delima is the piston height of 6 good m50vanos piston rod combo
    Only 4 M20 rods left and only 5 M20 pistons.

    I thought about having the Pistons machined down which is the easiest solution and running flat tops but I don't have a clue what kind of compression ratio that would leave me with. I have an 885 head which I can also have shaved down if need be to reach a compression ratio of 10:1 10.5:1 or I could make 11:1 work if need be. Any help anyone could provide will be greatly appreciated.
    Respectfully
    David
    Tags: None
    #2

    As found

    Knocked the pollen off

    Junk rods

    Good rods I wanna use

    Old vs new

    Comment

      #3
      Anybody have any input?

      Comment

        #4
        Get a set of good used m20 pistons off ebay for $100 and use the best ones.

        Comment

          #5
          I have installed m50NV rods into a stock I piston and 885 head. it was the smoothest m20 i've ever built. they are a good upgrade.
          the m50tu has 140mm rods and those wont fit in an m20.
          Much wow
          I hate 4 doors

          Comment

            #6
            The m50nv is 135mm right? So nothing is really changed right? Are the a lighter rod?

            Comment

              #7
              Flat tops would work if you had a 731 head.

              It's actually something I have planned if I decide to build another cheap M20. 731 head with B27/81mm crank, M52B28(135mm) rods and pistons with 1.12mm shaved off the pistons. Just a basic 2.7 but the longer rods/lighter pistons should make for a bit of an improvement.


              I agree with the others though. Just find a set of M20B25 pistons and use the best 6. The 885 combustion chamber is matched to the B25 pistons and they work pretty damn well together.

              Comment

                #8
                Originally posted by Navymr View Post
                The m50nv is 135mm right? So nothing is really changed right? Are the a lighter rod?
                Just look at them. The M20 rods are rather portly, the M50 rods are a good deal thinner. Should be a reasonable amount of weight reduction there.

                Comment

                  #9
                  I guess I'll be running to the pick n pull and seeing what's left out there half price weekend is coming up and I know there's a manual & m52b28 out there. Heck they have a 750il out there but I don't think I'm up to that task.

                  Comment

                    #10
                    If the rods have had that much hurt,
                    are you sure there's not some more damage in there?

                    Find a good used engine, drive the car, and THEN play with all the parts you
                    have left to see if you can make something out of them.

                    t
                    now, sometimes I just mess with people. It's more entertaining that way. george graves

                    Comment

                      #11
                      Everything else seems to be ok. No damage to the crank and all the rod bearings even looks good. Rod journals all looks great. Only other damage I've found was the rotor bug was rounded a bit where it mates into the cam gear. I was a machinist in the navy before being a diesel mechanic and engine builder but I wanted input on shaving the Pistons and what kind of CR to expect with the I head. Haven't had much constructive input so I'll figure it out

                      Comment

                        #12
                        Originally posted by Navymr View Post
                        Everything else seems to be ok. No damage to the crank and all the rod bearings even looks good. Rod journals all looks great. Only other damage I've found was the rotor bug was rounded a bit where it mates into the cam gear. I was a machinist in the navy before being a diesel mechanic and engine builder but I wanted input on shaving the Pistons and what kind of CR to expect with the I head. Haven't had much constructive input so I'll figure it out
                        I have a complete motor from a 87 325i I would be willing to part with if you would like. I got it cheap so ill let it go cheap I gave up the idea of the stroker motor for my old 325es

                        Comment

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