surrytop Posted August 26, 2014 Report Share Posted August 26, 2014 Hi,I recently had to drain the gearbox and the plug was extremely tight to undo.I am ready to rebuild the box but thought I'd try the drain plug before I started and it looks as if the thread in the gearbox is damaged.It is'nt that bad and a run through with a suitable tap should be ok,but does anybody know the size and type of thread? The car is a TR4A and while the box is'nt original to the car it's serial number is CT65895 with a 14mm flange.The drain plug is a magnetic one.Any help would be appreciated,Brian Quote Link to post Share on other sites
Lebro Posted August 26, 2014 Report Share Posted August 26, 2014 I may be wrong, but I believe the gearbox plugs are a BSP thread - probably ¼BSP. ( this size is the internal dia of the pipe, not the O/D of the thread) also the thread may be tapered, so you would need a tapered tap. AlanT may know better ! Bob. Quote Link to post Share on other sites
AlanT Posted August 26, 2014 Report Share Posted August 26, 2014 Its a tapered pipe thread I am pretty sure. !/4in seems too small, I'd guess 3/8 BSPT. According to my Zeus chart: 1/4in is 0.52in dia 3/8 is 0.66in dia This is for parallel, BSPP. I'd guess you measure the fat end of your plug. These both run 19TPI. If you try to measure TPI, remember the difference between fence-posts and fence-panels. Quote Link to post Share on other sites
surrytop Posted August 26, 2014 Author Report Share Posted August 26, 2014 Thank you for the info,I'm not too sure where I would obtain a tap of that description,thanks Quote Link to post Share on other sites
stillp Posted August 26, 2014 Report Share Posted August 26, 2014 From a good engineers' merchants. They might have to order one for you. Quote Link to post Share on other sites
graeme Posted August 26, 2014 Report Share Posted August 26, 2014 I have used this company before, good service. http://www.tapdie.com/html/bspt-_taps.html Cheers Graeme Quote Link to post Share on other sites
AlanT Posted August 26, 2014 Report Share Posted August 26, 2014 (edited) http://www.ebay.co.uk/itm/1-4-X-19-BSP-CARBON-TAPER-TAP-THREADING-TOOL-FROM-CHRONOS-ENGINEERING-SUPPLIES-/370761450996?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item56531ac5f4 http://www.ebay.co.uk/itm/Warrior-3-8-x-19-Tpi-BSP-Plug-Hand-Tap-v-/111354262867?pt=LH_DefaultDomain_3&hash=item19ed3b3553 Edited August 26, 2014 by AlanT Quote Link to post Share on other sites
Lebro Posted August 27, 2014 Report Share Posted August 27, 2014 With gearbox being aluminium, you could probably repair the thread by using a spare drain plug, cutting a few slots across the thread, & winding it in & out a few times. If you don't have a spare plug, any iron plumbing fitting of the right thread would do - easily obtainable from any plumbers merchants. Bob. (yes - 3/8" is more likely) Quote Link to post Share on other sites
RogerH Posted August 27, 2014 Report Share Posted August 27, 2014 Hi Brian, before you do anything establish exactly what thread you have in the gearbox. Although the male/female assembly will be BSPT (tapered - hence being tight) the female may actually be a plain straight hole (BSP) and the plug BSPT (tapered). It may be worth contacting one of the gearbox building chaps. Are you sure that the internal thread is damaged. Fitting a tapered plug into a plain hole may well distort the thread a little. Roger Quote Link to post Share on other sites
surrytop Posted August 27, 2014 Author Report Share Posted August 27, 2014 In the end I went to the garage who does my MOT'S and he recommended a small machine shop that he uses a couple of miles away.The engineer there checked the gearbox and plug,confirmed it was 3/8" BSP,and recut the thread using the correct tap and did'nt charge me!All I have to do now is rebuild the gearbox.Thanks for all the advice posted. Quote Link to post Share on other sites
AlanT Posted August 27, 2014 Report Share Posted August 27, 2014 (edited) Presumably you have read about fixing gboxes on VTR and Buckeye? This is quite a tricky mechanical job. I should consider finding someone to do it for you. I have a recent topic on here showing the tools I made for doing this. Edited August 27, 2014 by AlanT Quote Link to post Share on other sites
Richard V Posted August 30, 2014 Report Share Posted August 30, 2014 Hi, Just noticed this thread. I purchased a magnetic drain plug from Rimmers, which had the incorrect thread type. Luckily I noticed before installing as the difference was enough to damage the alu housing, but not easily seen at a glance. Perhaps it was this that caused the damage to the threads on your GB. GB rebuilding is great fun. Read buckeye, buy the right bits, and have a go. You will learn loads during the build, and it wont kill you if it goes wrong! Drop me a PM and I will dig out and send you some info on GB + OD building that I was given by a very knowledgable gent when building mine. (its done 10,000miles with no leakage or problems since) Cheers, Richard. Quote Link to post Share on other sites
AlanT Posted August 30, 2014 Report Share Posted August 30, 2014 Ah, the two mm's problem again. I'll make a list. This is a British Standard pipe blanking plug. Ten a penny. Quote Link to post Share on other sites
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