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Don't buy Chinese Turbos, eh? (Bastard threads)

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  • Don't buy Chinese Turbos, eh? (Bastard threads)

    Dad called me up today and said he needed a custom banjo bolt for a new turbo. M12x1. Seems rare, but ok. The old one was a pretty standard M12x1.25.

    Anyway, we make the banjo from brass as that was the only hex stock we had that was close. Go to thread it in, and it's much to big. Whaaa? So we start checking closer. The thread is really shallow so it's hard to get a good reading. It doesn't exactly feel like 1mm pitch, but definitely not 1.5. It's sized almost exactly to 7/16-20, but that only goes in like 3 threads. WTH? Amazingly dad has an M11x1.25 tap which was a good fit but the wrong pitch. So we made too test samples from aluminum, M11x1, and M11x12.5. It definitely wasn't the latter, but it was close to the former. Definitely not the exact right pitch as it started to rub off dykem unevenly as it went down. I think it was closer to 1.1 or so.

    At any rate, I made a stepped M11x1 banjo bolt for dad out brass. I'm sure the threads deformed some, but it seemed to tighten up good. I probably should have gone for 1.1 or so, but we were tired of F'ing with it. I just cut the thread to be a good fit on the pitch gauge as I didn't feel like doing a ton of math for a non-existent thread.

    Anyway, the bolt came out nice! I've barely turned any brass at all (pricey), but it sure does turn nice!

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    Turbo is a cheap, ebay "Turbo" brand turbo. Dad's choice. So what do you think. Proprietary thread, or general incompetence? I think the latter. I think it was threadmilled with a single point, I think they were off on both the diameter and perhaps the pitch as well, making for a thread that exists only on this run of turbos. At any rate that's my best guess. Anyone placing bets on if the damn thing works at all or blows up in the first five minutes. lol

    Don't buy cheap ****!
    21" Royersford Excelsior CamelBack Drillpress Restoration
    1943 Sidney 16x54 Lathe Restoration

  • #2
    Are you sure it was supposed to be a banjo bolt?
    Lots of turbos use either pipe threads or AN fittings. I've even seen BSPT used on rare occasions.

    Comment


    • #3
      Regardless of whether it was supposed to be a fitting, a bolt or a plug, it should have had a standard thread.

      And yes, banjos in that sort of setup are very common.

      Doc.
      Doc's Machine. (Probably not what you expect.)

      Comment


      • #4
        This might be a bit wide of the mark, but here goes anyway:

        You say that 7/16 x 20 almost fits. 7/16" is 11.11mm. 1/4"BSP parallel thread spec is 11.445mm diameter with 19TPI (=1.337mm pitch). And it IS a standard pipe thread, which would be not unexpected in such a fitting.

        Worth a try?

        Comment


        • #5
          There is little incentive to stick to standard sizes in automotive. Engineers are pushed to shave a few percent of weight from all components regularly.
          One million M11 bolts are also cheaper than one million M12 bolts.

          Comment


          • #6
            Nice!
            Brass and bronze are fun, aren't they? Turns beautifully.
            I always keep a few small sticks of brass around just in case.
            (I actually enjoy doing weird threads that are illegal in 39 countries....)

            (the easiest and cheapest turbos to work on are from CAT earthmovers.
            cost from 500 to 800 on Amazon believe it or not,
            uses a 2-bolt SAE flange for the oil, it's listed in MH)
            Last edited by nickel-city-fab; 07-18-2021, 09:05 AM.
            25 miles north of Buffalo NY, USA

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            • #7
              By in large the switch to a proprietary thread is usually a veiled attempt to capture the replacement parts market. Up until around WWII many manufacturers in this country and abroad used proprietary thread fasteners specifically for that purpose. I have several machines of the early 1900's vintage and have to be extremely careful when attempting to replace fasteners. When I got a machine from my FIL it came with a large number of taps and dies. I didn't realize at the time what they were for and almost tossed them in the trash. The first time I tried to replace a fastener I realized what they for.

              It seems like the world is reverting to this practice once again. In the recent years I have run across a number of relatively new machines with odd fasteners. Some have proprietary threads, others use proprietary heads as in odd hex sizes either internal or external. I'm sure the reasoning is to once again capture the replacement part market. There aren't enough of a particular size to make it feasible for an after market company to make them in volume. In some cases replacement fasteners aren't even available from the manufacturer. You have to either make your own, or buy the complete component.

              Comment


              • #8
                Current lathes and mills do not rely on gear trains for threading, one simply programs the thread lead and diameter.
                Producing a 21/64" 15 7/8 TPI thread is a simple matter of entering the dimensions.

                There are no Thread Police.
                If however your product literature claims the use of (insert published standard here) use it.
                Last edited by Bented; 07-18-2021, 10:18 AM.

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                • #9
                  Originally posted by projectnut View Post
                  the world is reverting to this practice once again. In the recent years I have run across a number of relatively new machines with odd fasteners. Some have proprietary threads, others use proprietary heads as in odd hex sizes either internal or external. I'm sure the reasoning is to once again capture the replacement part market.
                  I'm not sure "reasoning" even applies. I've had to work with a few electrical engineers over the past couple decades, and they seem to abhor anything like a standard solution. Every circuitboard is designed anew for the job at hand, past and future products be damned.

                  It would not surprise me to find that mechanical engineers are the same: design everything on paper by running the numbers for optimal part performance vs constraints (cost/weight), past and future products be damned. I'd imagine that lack of pushback from machine shops (as Bented says, modern machines will produce whatever crazy fasteners you tell them to) has just reinforced this behavior.

                  Originally posted by projectnut View Post
                  There aren't enough of a particular size to make it feasible for an after market company to make them in volume. In some cases replacement fasteners aren't even available from the manufacturer.
                  Yeah, repairability isn't high on the agenda. The majority of customers prefer to make their malfunctioning product Somebody Else's Problem, and either throw it away or try to unload it on some poor sod via Craig's List.

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                  • #10
                    Many, many years ago when I was working as a mechanic, we had a Fiat 124 come in for brake work. The car lived in a northern state with snow. ice, and salt all winter, so about three of the four bleed screws just broke right off. We took the brake parts to a local machine shop and asked them to sort out the broken parts and in time they sent the parts back with broken screws extracted but said they couldn't chase the threads with anything they had so it must be some bastard metric thread. After some thought and inspection, I realized that the name on the brake cylinder castings said "Girling". Ah, yes, it would seem a bastard in metric because it was simply an English thread. Problem solved.
                    .
                    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

                    Comment


                    • #11
                      M12 is 1.75, 1.25, 1.5 and 1mm pitch in order of commonness. As for m11, then that is a non standard size, I had a link to a very detailed thread chart from a USA based company, but it got lost when my Firefox went bad on me, the name might have had Millwauki in it. You were lucky to have the expertese to be able to make a custom one. Fortunately it is always easier to make a male thread to fit a female especially when the female is in an ackward position.
                      Last edited by old mart; 07-18-2021, 11:57 AM.

                      Comment


                      • #12
                        Originally posted by eric_h View Post
                        Are you sure it was supposed to be a banjo bolt?
                        Lots of turbos use either pipe threads or AN fittings. I've even seen BSPT used on rare occasions.
                        So no, not necessarily. It technically has an inverted flare at the bottom and uses a riser. Or at least one of his trucks did, I'm not sure which one. But the riser was the same standard thread, so it wasn't required. That would allow it to seal internally in case the turbo got corroded around the banjo washers and started leaking.

                        Originally posted by Mike Burch View Post
                        This might be a bit wide of the mark, but here goes anyway:

                        You say that 7/16 x 20 almost fits. 7/16" is 11.11mm. 1/4"BSP parallel thread spec is 11.445mm diameter with 19TPI (=1.337mm pitch). And it IS a standard pipe thread, which would be not unexpected in such a fitting.

                        Worth a try?
                        Mike I don't think you are off base at all. But I just referenced my machinery's handbook. The minor diameter is .393, much smaller than the .4506 of the 1/4-19 BSP. And it was certainly finer than 1.337mm pitch. Much closer to 1 if anything. So it's gotta be something else.

                        The AN suggestion by eric may be correct though, as it looks like they do have a 7/16-20 AN thread. But the flares on those would be opposite of what we'd need for that to work.
                        21" Royersford Excelsior CamelBack Drillpress Restoration
                        1943 Sidney 16x54 Lathe Restoration

                        Comment


                        • #13
                          Originally posted by Bented View Post
                          Current lathes and mills do not rely on gear trains for threading, one simply programs the thread lead and diameter.
                          Producing a 21/64" 15 7/8 TPI thread is a simple matter of entering the dimensions.

                          There are no Thread Police.
                          If however your product literature claims the use of (insert published standard here) use it.
                          I agree. However, it's supposed to be a "direct fit" replacement, made to Isuzu's exacting specifications. That's what they claim. Clearly, that is BS. Not only did dad have to spin all the components around to clock them right, but now these threads. I do not think they had any of Isuzu's specifications. I think they reverse engineered it in it's entirety.
                          21" Royersford Excelsior CamelBack Drillpress Restoration
                          1943 Sidney 16x54 Lathe Restoration

                          Comment


                          • #14
                            Metal Butcher: It seem like you were having trouble finding the original pitch. One method I use is quick and easy, that is to turn a wooden dowel to a diameter that is about .015" larger than the minor dia. of the thread in question. then I file a small taper on the end and screw it in the thread in question and remove. This will show you the pitch and the minor dia.

                            Sarge41

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                            • #15
                              Originally posted by sarge41 View Post
                              Metal Butcher: It seem like you were having trouble finding the original pitch. One method I use is quick and easy, that is to turn a wooden dowel to a diameter that is about .015" larger than the minor dia. of the thread in question. then I file a small taper on the end and screw it in the thread in question and remove. This will show you the pitch and the minor dia.

                              Sarge41
                              Sarge, damn that's genius! You guys are great! Thanks!
                              21" Royersford Excelsior CamelBack Drillpress Restoration
                              1943 Sidney 16x54 Lathe Restoration

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