Andy J Posted October 7, 2022 Share Posted October 7, 2022 Wondering if I have the skills to manufacture a main needle for an ST carb used on a Laser 75. First hurdle is that the thread is very fine possible BA but a couple of nuts I tried did not seem correct. So does anyone know what threading was used on this carb. Second problem is what angle is recommend for the chamfer and over what length. Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted October 7, 2022 Share Posted October 7, 2022 Not my field of expertise, but I seem to recall that ST used some imperial threads. IIRC, the rear crankcase cover screws were a BSF thread, so its possible the needle valves were similar. I'm sure Engine Doctor will be along shortly with more info. I think Motors & Rotors sold off all the ST spares to an ebay seller, and its possible they may be able to point you towards a supplier. Also, have you actually spoken to Laser? They may have some spares. -- Pete Quote Link to comment Share on other sites More sharing options...
David Davis 2 Posted October 8, 2022 Share Posted October 8, 2022 I believe that Gavin Carter makes needle valves for Super Tigre carburetters. I can find no evidence here: https://www.ebay.ie/str/gcpistonrings?_trksid=p2047675.m3561.l2563 but it may be worth your while to send him an email. Quote Link to comment Share on other sites More sharing options...
David Davis 2 Posted October 8, 2022 Share Posted October 8, 2022 Gavin Carter is also contactable here: https://www.facebook.com/gavin.carter.395 Quote Link to comment Share on other sites More sharing options...
Andy J Posted October 8, 2022 Author Share Posted October 8, 2022 Did send Gavin an email via ebay several days ago but yet to see a reply. When I get the chance will see if the broken part of the needle with the thread looks similar to a BSF reference sheet of sizes. Trouble is that my eyesight is not good these days. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted October 8, 2022 Share Posted October 8, 2022 Hello Andy . Sorry cant help with the thread fir ST needle. The thread is very fine though and I don't think it's a BSF thread. Check on spectre engine test s . If your eng8ne is on there it might tell you the thread ? Jon will undoubtedly know what thread is used . The last Laser I had with an old style ST carb I ditched the carb and fitted a later SC FS carb . Ran very well and plenty of second hand SC stuff still about. Just check the spigot size. You may still find a ST needle on ebay or in the classifieds on here or yhe BMFA. Quote Link to comment Share on other sites More sharing options...
Andy J Posted October 8, 2022 Author Share Posted October 8, 2022 Thanks ED, still like the idea of having a go at making one as it will be good practice for use of my lathe. Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted October 8, 2022 Share Posted October 8, 2022 1 hour ago, Andy Joyce said: Thanks ED, still like the idea of having a go at making one as it will be good practice for use of my lathe. 👍 Quote Link to comment Share on other sites More sharing options...
David Davis 2 Posted October 21, 2022 Share Posted October 21, 2022 I sent an email to Gavin Carter a couple of weeks ago asking when he will produce some more Super Tigre needles and I received a reply from him today saying that he will make a new batch once he has finished all of his current back-orders. Quote Link to comment Share on other sites More sharing options...
Andy J Posted October 21, 2022 Author Share Posted October 21, 2022 I also got a similar mail David. Also asked him what thread the ST needle uses as would like to have a go making one myself just for a bit of practice. Quote Link to comment Share on other sites More sharing options...
Andy J Posted October 24, 2022 Author Share Posted October 24, 2022 Measured up the broken part of the needle today and found there was 4 threads over 1/16 of an inch which equates to 64/inch. Diameter was 0.084 inch. Comparing this on a couple of sites would suggest the ST needle thread is a No 2 UNF thread. Quote Link to comment Share on other sites More sharing options...
David Ovenden Posted October 24, 2022 Share Posted October 24, 2022 (edited) If the ST carb and needle valve were designed and made in Italy I would have thought it would be a metric thread. But that's just conjecture on my part. From your measurements maybe 2mm x 0.4 pitch?? Edited October 24, 2022 by David Ovenden Quote Link to comment Share on other sites More sharing options...
RottenRow Posted October 24, 2022 Share Posted October 24, 2022 According to this site dedicated to control line models, the ST needle thread is 2.3mm x 0.4mm metric. http://controlline.org.uk/phpBB2/viewtopic.php?printertopic=1&t=4947&postdays=0&postorder=asc&&start=0&sid=aecebbd92758056b5c7f8f3ec2d6fca3 Good dies not cheap, but available here... https://www.tap-die.com/contents/en-uk/p620_2.3x.4mm_dies.html Cheapo versions available from Amazon etc. One die will last a lifetime of needles though. Brian. Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted October 25, 2022 Share Posted October 25, 2022 11 hours ago, David Ovenden said: If the ST carb and needle valve were designed and made in Italy I would have thought it would be a metric thread. But that's just conjecture on my part. From your measurements maybe 2mm x 0.4 pitch?? There are some Imperial threads on STs. IIRC the backplate screws are BSF! -- Pete Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted October 25, 2022 Share Posted October 25, 2022 (edited) Once you find the correct thread try Tracy Tools They are excellent to deal with and sell Taps and dies at prices and quality to suit your needs . Engine manufacturers often used odd sized screws etc as that can buy large quantities at a low price; or more likely you have to buy spares from them OS used 2.2mm screws on the small LA engines and I think on the earlier small FP engines for cyl head and backplate . Still available but a bugger to find if you dont want to pay stupid OS spares price . Edited October 25, 2022 by Engine Doctor Quote Link to comment Share on other sites More sharing options...
Andy J Posted October 25, 2022 Author Share Posted October 25, 2022 16 hours ago, RottenRow said: According to this site dedicated to control line models, the ST needle thread is 2.3mm x 0.4mm metric. http://controlline.org.uk/phpBB2/viewtopic.php?printertopic=1&t=4947&postdays=0&postorder=asc&&start=0&sid=aecebbd92758056b5c7f8f3ec2d6fca3 Just measured the needle again in metric and its 2.12mm so quite a bit shy of the 2.3mm Brian. 16 hours ago, RottenRow said: Quote Link to comment Share on other sites More sharing options...
Andy J Posted October 25, 2022 Author Share Posted October 25, 2022 (edited) Well if anyone has a spare M2.3 bolt they can send me, happy to try it on the pinch nut that sits on the top of the carb. Went through my box of metric & BA screws and nothing comes close. Just by chance I found that I had an M2.2 die and tried to thread it onto the broken needle. Certainly it appeared to accept the threading but after half a turn if locked up so it could well be an M2.3. Edited October 25, 2022 by Andy Joyce Quote Link to comment Share on other sites More sharing options...
RottenRow Posted October 25, 2022 Share Posted October 25, 2022 2 hours ago, Andy Joyce said: Just measured the needle again in metric and its 2.12mm so quite a bit shy of the 2.3mm Brian. Hi Andy, An external (male) thread will measure a bit less than the specified size (called the major diameter), this is to ensure clearance between the peak of the male thread and the internal (female) thread. Also your needle thread may be a little worn. Is your M2.2 die 0.4mm pitch (or is it 0.45mm)? If the latter then it would jam on the existing thread. Very unlikely to find an M2.3 bolt (x0.4), unfortunately. I have just measured the needle on my almost unused ST X45 and it measures 2.28mm o/d x 0.4mm pitch (ten threads in 4mm). Picture shows this measurement. The part number on the back of the packet of a new spare needle that I have for that engine is 2260353. Hope that helps..... Brian. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted October 26, 2022 Share Posted October 26, 2022 These measurements are close to 8 BA. Given the difficulty of measuring pitch accurately over a short length at this size and Peter’s recollection of mixed thread standards (he worked closely with the ST importer on radio related matters and knew him well) it might be worth considering as a possibility. Quote Link to comment Share on other sites More sharing options...
Andy J Posted October 26, 2022 Author Share Posted October 26, 2022 Martin, Did try an 8BA bolt in in the pinch nut and seem to recall it was a loose fit so don't think the needle uses a BA thread but it could of course have been a 7BA if such threading ever existed. Quote Link to comment Share on other sites More sharing options...
Andy J Posted October 26, 2022 Author Share Posted October 26, 2022 Was tempted to buy a M2.3 die but by the time I purchase a length of 2.5mm silver steel plus the die it woks out quite expensive. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted October 26, 2022 Share Posted October 26, 2022 Different diameters of steel tapered needle can be bought around £3 and be trimmed to length to be soldered into a brass, threaded, knurled thumb screw. Quote Link to comment Share on other sites More sharing options...
Doug Campbell Posted October 27, 2022 Share Posted October 27, 2022 I might have a spare . Will have a look later Quote Link to comment Share on other sites More sharing options...
Andy J Posted October 27, 2022 Author Share Posted October 27, 2022 Will a steel knitting needle be prone to rusting? Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted October 27, 2022 Share Posted October 27, 2022 2 minutes ago, Andy Joyce said: Will a steel knitting needle be prone to rusting? I should have noted Andy These needles are Stainless Steel. Most needles are some form of steel, and operate in an oily atmosphere, which aids longevity. This suggestion was made to bypass the difficulty of constructing the needle taper. Just trying to help. Quote Link to comment Share on other sites More sharing options...
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