J type gearbox drain plug thread?

[BartonStag]

Hi all,
I've just gone back to my J type gearbox two years after a rebuild!! It appears to have a hex headed magnetic type drain plug but it doesn't screw fully home, (it must go up to a sealing washer as the shank between the thread and the head is recessed). There was very slight damage to the threads but i'm confident they're ok now. Would like to run a tap through the gearbox thread - so can anyone tell me what thread type and size it is please?
cheers
Gord

[NeilR]

It's supposed to be a taper thread on the plug, so shouldn't screw fully home.

It's something like 5/8 UNC, but can't remember exactly.

[DJT]

3/8 x 18 NPTF Dryseal (taper thread)

[BartonStag]

IMG_3970.jpg OK fellas thanks for your replies. This photo (Rimmer Bros) is the drain plug i have. The thread looks parallel to me Dave TBH - so why the recess then if not for a sealing washer? Would've thought a "normal" taper thread plug with a square end would have sufficed. I remain more than a little confused at this end - though it doesn't take much i'll admit .
Cheers guys
Gord

[Lingen]

The original plug is tapered, but the threaded hole in the box is parallel sided. That is why the plug "Jams" in the hole and seals itself. The magnetic one ( I have one as well) is parallel sided, so needs a copper washer to make it oil tight. Fortunately the casting has a flat surface for it to seal against.
Mike.

[BartonStag]

The original plug is tapered, but the threaded hole in the box is parallel sided. That is why the plug "Jams" in the hole and seals itself. The magnetic one ( I have one as well) is parallel sided, so needs a copper washer to make it oil tight. Fortunately the casting has a flat surface for it to seal against.
Mike.

I understand what you're explaining Mike - but equally that's the issue! The magnetic drain plug we both have has a parallel thread - which can't fully screw into a tapered thread and seal onto a copper washer. The drain plug as far as I know is the one that was in the gearbox prior to it being reconditioned, so how did it seal before? I think I either have to get and fit a tapered drain plug or put a parallel tap through the existing thread to allow it to seal. I only know as things stand I can't seal the gearbox up .
Cheers
Gord

[jbuckl]

I understand what you're explaining Mike - but equally that's the issue! The magnetic drain plug we both have has a parallel thread - which can't fully screw into a tapered thread and seal onto a copper washer. The drain plug as far as I know is the one that was in the gearbox prior to it being reconditioned, so how did it seal before? I think I either have to get and fit a tapered drain plug or put a parallel tap through the existing thread to allow it to seal. I only know as things stand I can't seal the gearbox up .
Cheers
Gord

It’s a triumph… they all leak.

More seriously…. The female thread is parallel;
Original plug is taper seal.
New offerings are parallel, so require a copper washer to seal.
Simples.
Or… just continue with some combination that leaks… pet o.e.m.

[Lingen]

Gord.
AS I said (!) the threaded hole in the gearbox casing is parallel sided so the parallel sided magnetic plug will screw right in till it compresses the washer.
Mike.

[NeilR]

Just put a tapered plug in the hole. The one listed for Morris engine / gearbox / diff may well fit.

https://www.ebay.co.uk/itm/353094449313?hash=item523611b8a1:g:VukAAOSw8UdhrmL7&amdata=enc%3AAQAIAAAAwC%2BJMeccvV64bCHKUk1OZJGPgqQp9n1DOEDrJiGQHCMPdPXwGMB86dbew8vT64vMLXVPeAXzz1GvVK6y33rwd4Hmcqnyhe7yfTqeEmmx8myHFVoz0gHxAMGCriXLUssJ2gSCLqjAn8sjf4yHQPC7CMHdA7EV%2B7fsUNjciP4TLMYvuVEHdMLA%2BxiKmOb4DEK9guwArksnMorUXT4Q45A01rUJntF257lBcQ3A7vot1%2B0SPMU4CAOkFxw26vQyFGz6Aw%3D%3D%7Ctkp%3ABk9SR4rDtNLVYg

[Philip Wardle]

Magnetic tapered plugs are available e.g. https://www.opieoils.co.uk/p-84331-g...riantid=133188 with a 3/8 inch NPT thread, I have one in my diff and one in the engine sump.


IP03X-1.jpg

[BartonStag]

Magnetic tapered plugs are available e.g. https://www.opieoils.co.uk/p-84331-g...riantid=133188 with a 3/8 inch NPT thread, I have one in my diff and one in the engine sump.


IP03X-1.jpg

Nice one Philip
Many thanks
Gord

[BartonStag]

Gord.
AS I said (!) the threaded hole in the gearbox casing is parallel sided so the parallel sided magnetic plug will screw right in till it compresses the washer.
Mike.

Hi Mike,
My parallel drain plug wont screw home, that's the problem!! The thread in the gearbox maybe damaged - I don't know yet, hence I initially asked what the thread size is. Think i'll get another drain plug just to prove my original one is ok and take it from there.
Cheers
Gord