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2.85 (2.9) Stroker with S50 Crank - it lives!

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    #31
    Sounds like it's coming along... Check piston to head clearance with the gasket you're going to use. you can use some alloy shims under headbolts to work out what thickness MLS you need if unsure.

    or if you want to get a piece of alloy laser cut to same shape as an actual gasket for checking purposes let me know if have created a drawing and model.
    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

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      #32
      Yep I was definitely planning on doing that. Fortunately for me that will be a little while down the road, I have a good bit to do first on this motor.

      Comment


        #33
        As per your PM (displayed public for future searches since it's a common question):

        Originally posted by sert57
        I am working on building an m20 ( 2.85L using S50b30US crank) and wanted your opinion of if main cap bolts can be reused? The general consensus I recall reading is yes, but these are grade 10 bolts torqued to 45 ft-lb, and mine don't appear to have any yielding. What do you do for your builds?
        I have been following your thread ;)

        NOTE: This is my personal opinion based on experience, not rule/law.

        We have re-used the main cap bolts on many engines when they are not available. Despite what most manuals state (most automatically say "replace"). For some reason, it seems as if the part is not available, then they are in fact re-usable (again, IMO). In the cases where we have a client engine core missing the bolts, we align bore the main caps with ARP in place. We have not had a failure weather it be turbo or high RPM situations.
        john@m20guru.com
        Links:
        Transaction feedback: Here, here and here. Thanks :D

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          #34
          Lots of good info here. Sub'd.
          Originally posted by wholepailofwater
          Q
          :devil:


          WTB: Dove Grey e36 Front Door Panels (2 door)

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            #35
            What's your call on the head gasket thickness? Looks like the compression ratio is WAY high
            Drive it hard. Maintain it well.


            Convertible Technical & Discussion
            A Topless Memorandum

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              #36
              The pistons should be sticking out 0.4mm higher than stock. I was planning on getting a custom head gasket from VAC that can add up to 1.4mm thicker than stock. Not sure what exact size I need yet however,

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                #37
                0.080" should give nice tight squish, which means OEM 2.05mm might be good
                Last edited by digger; 11-14-2016, 01:50 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

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                  #38
                  So I was looking at the clearances more today, specifically between the con rod shoulder and the bottom of the bore. I put a piece of metal 0.020" thick in the gap and am estimating I have between 0.030" and 0.045" between the con rod shoulder and bore. Does anyone with more experience than I have input on if this acceptable? I think it will be ok, I'd be surprised if the crank moved that much (~2 times bearing clearance) and i doubt it would stretch that much. Then again I'm no expert.

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                    #39
                    Id probably want 0.080" myself

                    Just lightly chamfer the bottom of bore with due grinder and deburr it.
                    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


                      #40
                      I took a look at the clearance in question again this afternoon (Con-Rod shoulder to bottom of cylinder bore). I believe i am pushing playdoh to its practical limits. The method i used is outlined below:

                      1) squish play-doh in a vice to chips of relatively uniform thickness with a distinct cross-hatch pattern.
                      2) measure thickness of the chips
                      3) place chip in area of interest and rotate the engine through 1 cycle
                      4) remove and inspect chip, sectioning as needed.

                      I used 3 chip sizes for this: 0.2, 0.1, and 0.075" The last is shown below being measured. I estimate the precision of this measurement to be +-0.01".



                      The chip shown after 1 cycle. Note the raised area on the right with a thicker indentation to its left. This is from the con-rod shoulder bolt.



                      The chip section is shown below, with the area of interest towards the center of the picture. Note the thickness of the chip ( top of cross hatch - top of cross hatch) is estimated to be 0.075".



                      From this ( as well as the 0.1" chip) I conclude that the actual con-rod clears the block by about 0.075", whereas the con-rod should bolt only clears with about 0.05".

                      I think this should be enough clearance, but I am not positive. What do those of you with more experience than I think?
                      Last edited by sert57; 08-10-2017, 10:10 AM. Reason: updated photo links

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                        #41
                        Try some electrical solder. I find it works much better than clay (specially playdoh which is really too soft, I use modeling clay), and it holds the shape, much easier to use a caliper.

                        .050" is getting close. Remember rods can stretch near that longitudinally in use, the big ends probably not nearly that - but just something to keep in mind. Another ~.050" to .100" isn't much to remove from the block.
                        john@m20guru.com
                        Links:
                        Transaction feedback: Here, here and here. Thanks :D

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                          #42
                          I have nothing to add except that this is wonderful and keep moving forward
                          Simon
                          Current Cars:
                          -1986 BMW 325e & 1968 Datsun Roadster 2000
                          Previous Car Count : 21 ... and climbing...
                          Originally posted by Melon
                          Let it be known to all. Simon fucking keeps it real.

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                            #43
                            yeah if it rotates without resistance just chamfer/ roundover another 0.060" then deburr and then check with flexible mirror and GTG
                            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


                              #44
                              Firstly, I did the math on the TTY rod bolts, and found an as-installed factor of safety of yielding of 0.99. I then got new bolts. the old ones may have been fine, but Id bet the original torque value would need to be changed to compensate.

                              Finally got the grinding finished. An important note for others to consider with this is that the casting tolerances at the bottom of the cylinder bore are.... loose. to say the least. The casting line on the 6th ( i think ) cylinder was a huge contributor to the small clearance.


                              Measured all 12 clearances after grinding with play-doh and found them to be between 0.070 and 0.100" each. I then took some solder and attempted to measure clearance with it. the piece is shown below ( 0.070" ish OD, left end was gripped with needle nose pliers)



                              To decide if it was enough, I did some really basic math. The stackup includes the crank, bearings, rods, and pistons.

                              In the area of concern ( rod shoulder to block), the only time (i can think of) the forces will be pulling them together is for decelerating the piston at the top of the stroke. I chose to ignore any thermofluid concerns, and did a gross overestimation- I modeled 2kg pistons ( 5 times true mass ish) at 10,000rpm, modeling the crank as a single solid beam 1/2" thick, the width of the journal bearing, and 45mm long ( this is just one side of the crank with a minimal estimation). As i said - a gross overestimation. I performes simple kinematics to find piston acceleration, derived the vertical force required for this, and then used that force in a simple beam deflection model (del =pl/ae) Under these conditions and only analyzing vertical forces, vertical deflection of the crank end is 0.050".

                              bolts are pre-torqued significantly ( i did the math but the paper is in another state), but from bearing clearances of 0.0015", id be shocked if the rod bolts stretched enough to add 0.010", as they are yielded upon install and that kind of stretch would fail them very quickly.

                              I believe I am good to do final torque on the rods and mains.
                              Last edited by sert57; 08-10-2017, 10:11 AM. Reason: updated photo links

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                                #45
                                cool build. Interested to see how this turns out.
                                I'm in the process of building 2.9L stroker myself. I was looking at a lot of options myself. Unfortunately I do not have free access to the machine shop so financially it made more sense to go custom pistons. I would had to machine valve pockets in stock I pistons with my cam setup and that (in addition to the rest of machine work) changed my original plans.

                                Looking forward to the progress. To make this post useful.... when you will be doing your mockup and will need to install/remove the belt gear on the crank....pull the woodruff key and don't put it back until final assembly. It should save you from using a puller and makes the mockup easier.

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