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Rad drain tap hole thread

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Rad drain tap hole thread
Steve Bryant Offline
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#1
08-02-2022, 12:37 AM
Can anyone tell me the thread form and size of the radiator drain tap hole please?
Thanks,
Stephen
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Stuart Giles Offline
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#2
08-02-2022, 09:27 AM
1/4" BSP
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Steve Bryant Offline
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#3
08-02-2022, 03:08 PM
Thank you Stuart.
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dickie65 Offline
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#4
09-02-2022, 07:03 PM (This post was last modified: 09-02-2022, 07:06 PM by dickie65. Edit Reason: more info )
It is 1/4" BSPP ( Parallel ) Flange sealed with fibre washer.


Not 1/4" BSPT ( Tapered ) Taper lock thread, Ptfe or other pipe sealant used.

Both the above are BSP in form and pitch they must not be mixed.

I have just spotted where you are located in Canada.

In the USA they use NPTP and NPTT which will not fit in the Austin Radiator tank.
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Steve Bryant Offline
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#5
10-02-2022, 02:08 AM
I need to ease or clean the threads in the radiator as the new drain cock will only go in a few threads before getting very stiff. I'll look for a thread cleaning tool of some kind as the correct tap is something I don't have.
Cheers,
Stephen
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Bob Culver Offline
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#6
10-02-2022, 04:03 AM
Pipe threads , nomenclature, parallel vs taper,  application, BS vs NP etc seldom well explained but was in a post here some time ago. Might be worth searching for.
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Hugh Barnes Offline
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#7
10-02-2022, 09:43 AM
Have a care Stephen, if the new tap only goes in a few threads then tightens up, it may be because the threads on the tap and in the rad are different. If you 'clean' one of the threads up, you may end up ruining something - and if it were the threaded boss in the rad, you would be in trouble.... Don't rush into it...
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Stuart Giles Offline
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#8
10-02-2022, 10:25 AM (This post was last modified: 10-02-2022, 10:25 AM by Stuart Giles. Edit Reason: missing word )
As Hugh says, quite possibly a mis matched thread. You may have been given a 1/4" NPS fitting (National Pipe Straight) these are 18 TPI. 1/4" BSP fittings are 19 TPI. Some of the bigger NPS/NPT fittings have the same thread count as BSP items, but they still Won't make a good seal as the thread form is also different.
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Steve Bryant Offline
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#9
10-02-2022, 02:33 PM (This post was last modified: 10-02-2022, 02:34 PM by Steve Bryant.)
The drain cock is from a cherished supplier so I have to assume the thread is correct. I have other drain cocks from 50's BMC cars and they also start to seize up after a few turns into the threaded hole. This leads me to thing that the threads need to be cleaned.
Stephen
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Ruairidh Dunford Offline
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#10
10-02-2022, 02:45 PM
Have you considered that the threads into the radiator are not as supplied originally?
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