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Yet another S14B25 rebuild thread

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  • I would turn to a pro to fix that...given what S14 heads are currently going for...

    It can definitely be repaired. Worse case scenario would be to add a weld bead to the damaged threads then re-machine it. But it is going to require someone competent welding aluminum, and a decent machinist. Hopefully you can find one person who is both to keep costs down. Honestly if someone knows what they are doing, it should only be two or three hours of work max. The only small stumbling point would be the required tap to re-cut the threads....whatever the thread size is, I doubt they will have the tap lying around. I have found that when specialized tooling like that is required for a job, usually the machinist requires you to pay for at least half of it.

    If indeed the threads are "gone" (it looks like they are) I definitely wouldn't try fixing it by hand. You will likely just dig the "hole" deeper. The threads are so shallow there is no way you will be able to accurately machine out the hole and cut the threads perfectly straight without a mill.

    It's funny, many years ago building my engine I too thought it seemed like a good idea to remove that fitting and replace the "O" ring. But I quickly realized it was corroded in place so tightly, it wasn't coming out without damage.
    Last edited by Ironhead; 01-03-2018, 12:52 PM.

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    • I can feel your pain, if it is any consolation you did your best there really there is no going back once loosened and the thread picks up. I agree with Brian time to ask around for the best possible place to get it fixed.
      Just throwing an idea out there, new bung machine the threads off and have it welded in to the head then head pressure tested and skimmed.

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

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      • A machine shop with a horizontal borer would be able to recut the thread. Probably for less cost than an M36 tap.
        Sport Evo No.47

        My Sport Evo Restoration

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        • Thanks for your replies and ideas on the best way forward. I am also quite sure that the thread was damaged as soon as I loosened the fitting, even if this didnít require an abnormal torque. I just wish I didnít touch it, and initially I didnít intend to, but after replacing the O-ring at the bottom of the oil pan (which I would also consider as an optional replacement if it was not leaking before), I saw that I also still had the O-ring for this fitting lying around so I thought why not replace it while I have easy access...

          Further to the two ideas proposed by you guys, which probably both involve a dismantling of the head wih the associated cost (mainly head gasket and bolts) and time, as well as a skimming of the head a second time because of the involved welding, I have thought of a possible repair with Helicoil thread inserts. The thread seems to be an M36x2 (I can only confirm for sure as soon as I have the new fitting). V-Coil, which is the German version of Helicoil, offers the following:
          https://www.voelkel-shop.com/en/thre...04062-m36.html

          They specifically write that the kit is designed for thread cutting by hand, so I wonder if this would be an alternative. The advantage would be that the head would not necessarily need to be dismantled again, if I find a way to keep the aluminum chips out of the head and block. This could probably be achieved by constant compressed air flushing of the water channels, blowing out the chips out of the same opening where the thread is being cut. What I donít know is how the bore is brought to the correct diameter before the thread cutting, because I doníít see how I would drill a clean hole of maybe 37mm by hand. What are your thoughts regarding this option?

          Tomorrow I will call my machine shop and ask them what they would recommend doing. Whatever the solution will be, I think I will definitely have them perform the work, as I donít want to risk damaging it further.

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          • I think helicoiling is probably the easiest and most suitable solution here. However because of the size of the hole I would look to get it done at a machine shop, otherwise thereís a risk you damage the hole further.

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            • The thread repair kit might work, as long as it is done in a machine shop type setting and the hole is drilled out/tapped in a mill by a competent machinist. I do have concerns though about using a thread insert in such a shallow hole....roughly 2/3 or 3/4 of the repair insert would need to be cut off, and I am not sure how stable the insert would be after that was done.

              Plus the thread repair kit is so expensive....I still think welding and re-machining is your best option. It sounds complex but it would be a piece of cake to someone experienced in this sort of thing.

              I wouldn't worry too much about having to dismantle the head. Perhaps 30 minutes work is all that amounts to.

              Find the right machine shop and get their opinion....since they will be doing the work.
              Last edited by Ironhead; 01-04-2018, 03:31 AM.

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              • I think the advice on the plug is solid. I would most definitely turn to a machinist for that. Trying anything that big by hand is certainly asking for trouble.

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                • The typical minimum depth for an insert is 1D, that is 36mm in this case. The only options are;

                  1, Have a machinist clean up existing thread and if serviceable, fit new plug.

                  2, If not serveacle, weld up and machine new thread and counterbore. Then fit a new plug.
                  Sport Evo No.47

                  My Sport Evo Restoration

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                • Yesterday I contacted V-Coil by email to ask if it's ok to cut the inserts to a shorter length and they confirmed that this is not a problem. I think the reason why they have the minimum length of 1D is that if you want to be able to load the thread with the full nominal torque of that specific bolt size, then a shorter thread length than 1D will not be sufficient. This is however not the case here, as the load on the thread will be significantly lower than the nominal torque of M36x2, which would be 2200Nm with an 8.8 bolt. Nevertheless, I am also unsure if having only maybe 4 or 5 turns of the insert which can engage in the head is sufficient.

                  Regarding the serviceability of the existing thread, I think that this will not be possible. The inner diameter of the bore is now approximately 35mm, while the nominal inner diameter of an M36x2 thread would be 34.21mm.

                  I tried to reach my machinist today, but it seems that they are closed this whole week. So I will have to wait until Monday to get their opinion.

                  Thanks for your help so far and I'll keep you posted!

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                  • Hi
                    If you look at the bung and understand where the o ring seals, which is right where you would be cutting a thread for a thread insert or helical that is what I see it could be very problematic with this type of repair. One possibility is to use a large soft alloy washer on the flat flange of the bung to seal it up.

                    If the bung is 36mm thread probably cut a 38mm thread for the helical/insert.

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

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                    • You are absolutely right, the O-ring would sit exactly where the helicoil insert would be. I think however that the solution you propose with the soft alloy washer should be feasible. Worst case, it could be sealed up with liquid sealant on the flat flange.

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                      • Sealing it won't be a problem at all once the threads are repaired.

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                        • If welding is not an attractive proposition, there may be another option. Machine the existing threads our and recut a larger thread. Then either have a new connector made to suit the new thread size or make an insert to accept a new original connector, if they are not NLA.
                          Sport Evo No.47

                          My Sport Evo Restoration

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                          • I like that idea. The original plug is still available from BMW, but a custom made part would certainly be the nicest solution. Would it be preferrable to have that part made out of stainless steel instead of aluminium? My understanding of galvanic reactions is that the aluminum plug should actually not react with the cylinder head, as they are both aluminium, compared to zinc plated carbon steel bolts installed in the same head, where some reaction should theoretically take place. Strangely, in real life, zinc plated steel bolts or fittings are always easy to loosen in aluminium engine parts, compared to this aluminium plug. Is this only because of the water which is involved here, compared to other bolts or fittings, where oil or no other media is involved, or is there another explanation?

                            Cheers,
                            Marc

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                            • I'm not up on galvanic corrosion. An aluminium plug would probably last 25yrs. Is that a problem for you :-)
                              Sport Evo No.47

                              My Sport Evo Restoration

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