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  • Yet another S14B25 rebuild thread

    Hello,

    during the rebuild of my M3 Sport Evolution which I started several years ago, I only made a “small rebuild” of the original S14B25 engine. Unfortunately I never got the car on the road since the rebuild, as I had serious problems with a whining noise coming from the timing chain after reassembly of the engine. Some might remember my thread about this issue. Unfortunately, I then had very little time to work on the car and thus never really found the source of the problem. Fortunately, I now have some spare time on the week-ends, so I decided to finally finish my project.

    The initial plan at the time was to only make a small rebuild of the engine, as it had only 100k km on the counter. Compression was fine and it was running without any issues. I therefore only replaced rod and main bearings, crank (the old one was scratched), oil pump, timing chain and sprockets. As I didn’t remove the cylinder head from the block, I wasn’t able to replace the timing chain tensioner rails. My assumption was always that the whining noise generated by my engine was due to the fact that the new chain was running on the old tensioner rails. I’m not (yet) sure if this was really the reason for the noise, but I finally decided to disassemble the engine once more in order to replace the tensioner rails. As the replacement of these rails requires the removal of the cylinder head from the block, it was clear for me that this time I was going to completely dismantle the engine and to check the bores etc. to find out if something else needed attention.

    I will use this thread to post photos of my rebuild, keep you informed about the status and of course to ask your opinion. The attached pics were taken during disassembly of the engine.

    After the first look at the cylinder bores, I found that they looked surprisingly good. The hone pattern is visible almost everywhere. I used my newly acquired dial bore gauge to measure out-of-round and taper. I’m certainly not a specialist in measuring cylinder bores, but I think that these values are sufficient as a first assessment.

    Cylinder Out-of-round Taper
    1 0,019mm 0,015mm
    2 0,027mm 0,025mm
    3 0,018mm 0,019mm
    4 0,006mm 0,020mm

    The out-of-round tolerance of the S14B23 is 0,005mm, for taper it is 0,01mm. I figured that the S14B25 will not be significantly different. Does anybody have any BMW documentation with the correct tolerances at hand?

    The table above clearly shows that all values are out of tolerance. Even if my measurements are maybe not spot-on, I think that it is safe to say that the cylinders will need to be bored. What do you think?

    Unfortunately, it seems that new pistons in over sizes cannot be purchased new from BMW anymore. What would be the best replacement after-market pistons? I am not interested in modifying the original engine compression or other parameters; my target is to do a stock rebuild.

    After measuring the cylinder bores, I made a last detailed inspection of the cylinder bores, and found something very strange at the bottom of cylinder n 2 bore, see attached photo. It almost looks like a crack, but I cannot feel anything when going over it with my fingernail, and why would a block crack at this position? What is your opinion about this?

    I hope that my thread will have something interesting in it for everybody here. Looking forward to hearing your comments.

    Cheers
    Marc

  • #2

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    • #3

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      • #4
        Wow...that last photo sure looks like a crack. Hard to imagine what else it could be.... Make sure whatever shop you choose for the bores magnafluxes the block prior to doing any work. It actually looks like there are faint rust stains from coolant leaking through.....I hope I am wrong.

        As far as rebuild cylinder specs, I have never seen ones specifically for the 2.5 Sport Evo engine, but as you said I think you would be safe in applying the 2.3 specs.

        For pistons, there will be no clear answer on "best". If indeed OEM is not available, I think your only choice will be to go with an aftermarket forged piston. Wiseco, JE and CP/Carillo are the manufacturers of most of them on the market....and the last two can custom make pretty much anything you need.

        If indeed that is a crank in your block...you will need a new block anyway....and then OEM pistons are an option again....
        Last edited by Ironhead; 03-13-2016, 10:20 AM.

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        • #5
          Hi Marc,
          I think the first step is to drop the block off at the engine reconditions for crack test of that bore, that will leave you two options for that block.
          If it is cracked replace the block or sleeve that cylinder, if replace the block it will come with new pistons.

          I would not be concerned at all with the readings you have measured, the engine is at 1/2 life should be able to go easy 250,000km before really requires boring, the measurements you have at worst are 0.025 which is slightly under 1 thousand of an inch. Manufacturing tolerances probably was not perfect in the first place.

          Depending on the out come of the crack results you could ask for acid bath and power hone, the power hone is the finish hone they use when cleaning up after boring and will remove any slight irregularities in taper/out of round leaving ideal surface for rings to bed in to.

          With pistons you have the option to reuse yours or I see new 2.5 original size pistons for sale quite often on this web site and eBay, if you could get your hands on them would have new pistons and rings for less than $400.00.

          Expect wine when the engine goes back together it does calm down it is just how they are especially when cold after full o/haul.
          Dave.


          E30 M3 1987
          Mini Clubman GT
          BMW E36 323 Msport
          Toyota Corona
          KTM 200EXC
          Honda CB50 (1979)

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          • #6
            Marc:

            Def good info from Irionhead and Dave. First stop should be Magnaflux test of #2 bore. If it's cracked (def looks weird...) it will show then.
            I had a 2.5L block crack from the bottom of the cyl linearly upwards. It was cracked into the cooling jacket. After Magnaflux test, I got the block sonic
            tested, and there didn't seem to be less material in / around the crack. No real explaination why it cracked, but it did! I had coolant in the cylinder and
            white smoke out the tail pipe.

            Ron C.
            Ron ///Man

            • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
            • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
            • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
            • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
            • '89 M3 M3T / ITR Club Racer
            • '94 Spec E36 - Eh....
            • '09 M3 - Tarmac Terrorist
            • '04 330Xi Sport 6 Speed - Snowmobile
            • '07 530 Xi - Highway Star
            • http://www.imwcarparts.com/e30-m3-parts.htm


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            • #7
              Originally posted by Ron ///Man View Post
              Marc:

              Def good info from Irionhead and Dave. First stop should be Magnaflux test of #2 bore. If it's cracked (def looks weird...) it will show then.
              I had a 2.5L block crack from the bottom of the cyl linearly upwards. It was cracked into the cooling jacket. After Magnaflux test, I got the block sonic
              tested, and there didn't seem to be less material in / around the crack. No real explaination why it cracked, but it did! I had coolant in the cylinder and
              white smoke out the tail pipe.

              Ron C.

              Ron,

              Have you ever heard of a 2.5 block being successfully sleeved? I was always under the impression that it was impractical (nothing is "impossible") because the bores are so close together...

              But as new blocks become more and more expensive....if a shop can figure out how to successfully sleeve them it would really be a nice development.

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              • #8
                Hi Ironhead, Dave and Ron,

                thanks a lot for your answers. Your opinion confirms my initial thoughts as well. I will definitely have the block crack tested at my engine shop, but I have little hope that it can be reused...

                I would also be interested if someone successfully sleeved an S14B25. The cylinders being very close together I would however be concerned that this would probably not be a very durable solution. I will definitely also ask my engine builder his opinion and let you know.

                According to a BMW online shop in Germany, it seems that the S14B25 block is still available, but only without pistons (part number 11111315501). The block including pistons (part number 11111316977) seems to be NLA. The original size pistons however seem to be available (part number 11251315965), so I see no reasons why the block including pistons shouldn't be available... If anybody has a block or pistons available for sale, please let me know.

                Marc

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                • #9
                  I have a set of stock pistons with rings if you need them.
                  Sport Evo No.47

                  My Sport Evo Restoration

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                  • #10
                    Thank you Steve, I will contact you via private message.

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                    • #11
                      Originally posted by Ron ///Man View Post
                      Marc:

                      Def good info from Irionhead and Dave. First stop should be Magnaflux test of #2 bore. If it's cracked (def looks weird...) it will show then.
                      I had a 2.5L block crack from the bottom of the cyl linearly upwards. It was cracked into the cooling jacket. After Magnaflux test, I got the block sonic
                      tested, and there didn't seem to be less material in / around the crack. No real explaination why it cracked, but it did! I had coolant in the cylinder and
                      white smoke out the tail pipe.

                      Ron C.
                      That does indeed look like a crack.

                      Unfortunately the cast surfaces are prone to bad surface finish and inclusions of carbides etc. Especially an issue in the water jacket where they can't be machined off.

                      These defects massively reduce the fatigue life by creating a stress concentration where the crack initiates.

                      Top level motorsport engine blocks are machined from solid to avoid this issues.
                      If everything seems under control, then you're just not going fast enough...

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                      • #12
                        Thanks for this interesting input Caneswell. This could indeed explain the form and orientation of the crack. I've never seen a cracked block before, but I always assumed that they are more prone to cracking in vertical direction (like Ron mentioned above).

                        I had a further detailed look at the bores today and I found that on the top of cylinder 4, there's a very similar defect than the one on cylinder 2, but smaller, see attached photo. This one is very hard to see with the bare eyes, even with a flashlight. The camera flash magically makes it visible.

                        I am now also quite concerned about the condition of the cylinder head. I assumed that the appearance of the cracks in the block must be related to a cooling issue in the past. If this really was the case, I would assume that it is quite likely that the cylinder head is damaged as well. Does this make sense to you, or could the cracks in the block also be linked to fatigue only? Anyway, I will try to dismantle the cylinder head as soon as possible and bring it to the machine shop for inspection together with the block.

                        Cheers
                        Marc
                        Attached Files

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                        • #13
                          Could the whining noise be caused by the chain not running properly over the idler gear underneath the intake cam gear? It wouldn't be the first time the idler gear is shifted and the chain runs only one single row over the gear.

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                          • #14
                            One of my initial thoughts regarding the whining just after the first run was also linked to that idler gear. In fact, I then found out that I installed the idler gear in the wrong direction, i.e. with the shoulder facing forward. Even if the ETK picture clearly looks like the shoulder should in fact face forward, I later found out that it actually should face backward, according to the BMW workshop manual. So I dismantled the chain drive to change the orientation of the chain gear and saw that the gear already showed some wear from the contact to the cylinder head inside wall. I was almost certain at the time that the whining noise must be gone when reassembling the chain drive with the idler gear in the correct direction. However, unfortunately nothing changed with the noise...

                            As I paid lots of attention regarding this gear during reassembly, I am sure that the chain was running on both rows of the gear.

                            Nevertheless thanks for your comment, I wasn't even aware that it's possible to install the chain with the idler gear shifted by one row.

                            Cheers
                            Marc

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                            • #15
                              Today I dismantled the vibration damper, the flywheel and finally the crankshaft from the block. The block is now ready to go to the engine shop. I'll try to find some time until the week-end to dismantle also the cylinder head to bring both parts to the engine shop for inspection.

                              Attached I included some photos of the upper main bearing shells (the lower shells look similar). At first I didn't really understand why the shells looked so worn after having started the engine maybe 10 times, without any street use (due to the chain noise problems). After a closer look, I figured that the worn coating is maybe just something like a break-in coating on the bearing shells? What do you think, is this normal? Is it safe to reuse these shells, or is it better to replace them by new parts in order not to risk anything?

                              Cheers
                              Marc

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