Colin Posted February 17, 2023 Author Report Share Posted February 17, 2023 Hi Morgana, Wow, you've got the gear allright! Were that me, finding the 34 a better fit, (and it tightened down acceptably) I'd just assume that the 34 was cutting it's own new thread in the bore as it screwed through. In my world, that's be job done!! However, you're absolutely right - what a Faff, with anythung else, not least my trusty butterflies! Best, C. Link to comment Share on other sites More sharing options...
Morgana Posted February 22, 2023 Report Share Posted February 22, 2023 What I'd really like is to make a large board with every imaginable set of nuts and bolts mounted on it to check threads... Gauges are all right, but it's no substitute for putting a nut on a screw and finding it binds after a couple of turns! Individual go/no go gauges are mightily expensive. 34TPI doesn't exist as a thread - the used pitches are 24, 32 and 36 because they have more factors. Metric 0.75 pitch does seem to be the only answer. I've had an e-mail from the Carburettor Doctor, who says the threads are all metric. Interesting, as the screws don't fit my M4.5 die and an M5 nut is not a good fit. I'm going to try drilling and tapping an M4.5 hole in a piece of scrap. Link to comment Share on other sites More sharing options...
Colin Posted February 22, 2023 Author Report Share Posted February 22, 2023 The Good Doctor maybe has a point? Solex are French, aren't they/weren't they?? So unlikely to have used our old imperial measures?? Please shoot that down if incorrect - I haven't googled them!!🙂 Link to comment Share on other sites More sharing options...
Morgana Posted February 27, 2023 Report Share Posted February 27, 2023 Yes, it would make sense, although I can also imagine a 1950s executive retooling the licensed products for a thread common in British usage! Aren't there engines from some British car manufacturer with Whitworth heads on metric screws so they didn't have to buy new spanners for the whole company after taking over a French factory? However, I think I've solved the mystery. After a tapped M4.5x0.75 hole was obviously too small, and attempting to run an M5x0.8 die down the screw didn't work I decided it had to be an M5x0.75 thread. Which doesn't exist in the Renard scale of useful sizes, nor in any of my thread tables. However, running an online search for this on the off chance threw up a company producing M5x0.75 taps and dies, and this link for carburettor screws for Citroën 2CVs... In conclusion, whatever I do will be very awkward for a future person (or me) to identify! Maybe I'll just use M5x0.8 Helicoils and be done with it. Why they chose a thread between the standard M5 series (coarse 0.8, fine 0.5) I don't know, especially going finer than normal when it's going into alloy where stripping is a danger! Link to comment Share on other sites More sharing options...
Colin Posted February 27, 2023 Author Report Share Posted February 27, 2023 No-one can fault you for effort, and expertise Morgana!! And Congrats for locating said company! Happy Ending! 😃 Link to comment Share on other sites More sharing options...
Morgana Posted February 28, 2023 Report Share Posted February 28, 2023 Well, -ish Colin! 😉 Useful if the original holes were OK, but since I need to use something else for the stripped ones I'll have to hope 5x0.8 Helicoils work so that at least the major diameter is the same as the originals. Anything larger I fear might be getting a bit close to the edge of the carburettor casting. The Helicoils of that size use a tapping drill of 5.2mm so it might still be OK to return them to an M5 thread once the thickness of the insert is taken into account, as the stripped ones can have a 5mm screw pushed through but it's not loose. An alternative could be to use one of those metal epoxies to rebuild the original threads, but as the car's needed for work I don't want to risk putting the fuel system out of action while I find it doesn't work, or at least not without a spare carburettor to practise on... Glues like that seem a bit too good to be true! Link to comment Share on other sites More sharing options...
Colin Posted February 28, 2023 Author Report Share Posted February 28, 2023 👌🙂 Bonne chance!! Link to comment Share on other sites More sharing options...
Morgana Posted July 13, 2023 Report Share Posted July 13, 2023 I can say that M5x0.8 Helicoils have been holding things down since February. The only blip has been last week when I noticed fuel leaking and found the screws had been loosened, I guess by vibration. I may have to thread-lock them. Link to comment Share on other sites More sharing options...
Colin Posted July 13, 2023 Author Report Share Posted July 13, 2023 Hi Morgana, Well done for achieving that outcome - if you threadlock them won't that make future dismantling & servicing a bit awkward?? I'm happy with my little butterfly nuts, if you'll pardon the phrase! The wings give me something to really tighten the two parts together. I've not noticed any leaks round the threaded body of the bolt & nuts, given they're smaller diameter than the original screws - tells me that the two part surfaces are nice and flat and that the joint is tight enough not to provide leakage. Well done for noticing it - under the pancake filted cover, it's easy to forget about the carb. :-) Link to comment Share on other sites More sharing options...
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