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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17386   
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No, the head is not helicoiled from new, nor is the head on the TDCi. Threads cut straight into the alloy.
If you think about it, even if you helicoil the hole, you still have a thread cut into the alloy of the head, it is just a bit bigger. |
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17th Jun 2020 12:48pm |
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| sako243 Member Since: 08 Jul 2014 Location: Wales Posts: 1218  
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Is that another cost saving measure? Ed
82 Hotspur Sandringham 6x6 95 Defender 110 300Tdi |
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17th Jun 2020 12:51pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17386
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No, just second-rate engineering. One it is out of the factory door, why care?
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17th Jun 2020 12:55pm |
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| landy andy Member Since: 15 Feb 2009 Location: Ware, Herts Posts: 5707 
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Isn’t that the point of the stud? So that you are not repeatedly using an alloy thread.
It obviously can’t be that weak otherwise it would have pulled the stud out of the head, not snapped it, and the original poster wouldn’t have the issues that he does. |
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17th Jun 2020 1:14pm |
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| sako243 Member Since: 08 Jul 2014 Location: Wales Posts: 1218
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I guess that argument could be made but cutting threads in aluminium is very dependent on the thread pitch and depth to sustain clamping forces. The default should be not to cut threads directly and you have to justify why it's valid rather than the inverse. Ed
82 Hotspur Sandringham 6x6 95 Defender 110 300Tdi |
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17th Jun 2020 1:25pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17386
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It is entirely normal for threads to be cut in alloys and there really is not problem, you just select a thread form and size that will carry the required load (generally you'd use a coarser thread in a soft material so the thread dimensions are larger).
Absolutely right about the stud, the idea being that the bit that you're likely to remove more often is the steel nut from the steel stud. I can't remember the spec for the TD5 studs, but if you go back to the days of pre-metric engineering you'd usually find that the stud had a fine thread at one end for the nut, and a coarse thread at the other for the head. The ISO metric thread system now in use has largely resulted in the use of coarse series threads for everything, and it is likely that he studs on the TD5 and the TDCi are a ISO metric coarse series thread at both ends. |
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17th Jun 2020 1:29pm |
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| sako243 Member Since: 08 Jul 2014 Location: Wales Posts: 1218
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Fairly sure the 300Tdi has the same pitch and length on both ends of the stud too. Ed
82 Hotspur Sandringham 6x6 95 Defender 110 300Tdi |
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17th Jun 2020 1:33pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17386
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I don't really understand the point you're making, if you fitted a Helicoil or Timesert or any other kind of insert you are still cutting a thread in the alloy. I've never seen am internal combustion engine with the manifolds bolted through from one side of the head to the other! What's the "inverse" of cutting threads directly? Very often now for cheapness car manufacturers will use thread-forming fasteners (such as Taptite screws) to roll the threads directly in the alloy part during assembly. |
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17th Jun 2020 1:34pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17386
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The 300Tdi will be a metric engine too, I would think.
With the adoption of the ISO metric coarse series thread form as a national, in fact international, standard, there was a general move away from fine threads except where they were specifically necessary. Your wheel nuts, for example, are an ISO metric fine series M16 thread, because they'd probably work loose if they were "normal" M16 unless some form of (non-reusable) stiff nut such as a nyloc was used. |
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17th Jun 2020 1:37pm |
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| sako243 Member Since: 08 Jul 2014 Location: Wales Posts: 1218
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Should point out my main experience has been with much finer threads in aluminium (sub 6mm) so I think there's a fair difference there because you can't get away with coarser threads. What I meant by "inverse" was that the default "attitude" was that threads should not be cut into aluminium, if you needed some threaded feature then Helicoil / equivalent was preferred. If you needed a threaded feature then you had to be prepared at design review / sign-off to justify why you needed a threaded feature in the aluminium, if you didn't use a helicoil you again had to justify why not. Whereas if you were going into steel then you could just tap threads willy nilly (i.e. the default choice could be the inverse). I'm not saying that threads in aluminium were not allowed but because of the softer material the people reviewing the design / signing it off would ask the questions to make sure you'd given it some serious thought. Ed 82 Hotspur Sandringham 6x6 95 Defender 110 300Tdi |
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17th Jun 2020 1:45pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 17386
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Thank you, I now see exactly where you're coming from. There is indeed a huge difference between small threads and large ones, and of course the softer the alloy the bigger the problem.
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17th Jun 2020 2:34pm |
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