Series 1, 2.0 Petrol, Core Plugs

[David Sparkes]

The engine isn't in front of me, but I'm told it's a spread bore 1997cc petrol engine, and was built in 1956.

One of the core plugs (not sure which) has corroded to the point of leaking.

Replacements have been supplied, but the rusty thread in the block needs cleaning.

What's the thread?

The man selling the plugs said 'some sort of BSP', but the plugs are ~1" OD, and 16 TPI, which doesn't marry into any table of BSP threads that I can find.

LRSeries.com list these plugs at http://www.lrseries.com/shop/product/listi...G-THREADED.html

RTC4250 - CORE PLUG THREADED -

Applicable Models: Land Rover Series 1,2,2A,3 all models , 4 & 6 cylinder. Various other models apps. Inc TDi

Product Description: 1" Threaded core plug.

S/S 247127

S/S 518272

Can be used for 210492, requires re thread to 7/8".

That last comment implies they know the thread form, but I can't get an answer on the phone right now.

Any knowledge here I can tap into? (Groan).

Thanks.

[Les Henson]

Would the original be whitworth I wonder?

Les

[David Sparkes]

The supplied replacements do 'more or less' fit, but not well.

So, the ~1" is correct.

The replacements are definately 16 TPI, but I can't be absolutely certain that this is correct for the block.

The BSP size would be either 5/8", with an OD of 0.902 (unlikely, that's 1/10" undersize), or 3/4", with an OD of 1.041" (41 thou oversize? Perhaps just possible).

BUT, both have a pitch of 14 TPI.

1" Whitworth is 8 TPI

1" BSF is 10 TPI

1" UNC is 8 TPI

1" UNF is 12 TPI

LRSeries.com have responded to say they think the threads are BSP, adding that the pipes for the arctic heaters screw into these holes 'that's why I thought they were BSP'. Interesting angle, but if true it means the 16 TPI supplied is rubbish.

Cheers

[secondjeremy]

I don't suppose its metric fine? - 24mm - pitch 1.5mm which I reckon is 16.93 tpi.

I'd have thought it unlikely anyone had metric fine kit in the 50's - let alone use it for a core plug - but I've been trying to size the old style disposable cannister oil filter fittings from the block to the filter - and all seem to have about the same pitch regardless of diameter at probably 26 tpi - which is bicycle thread - surely not?

[Phil Hancock]

1" x 16tpi = 1" conduit thread covered in BS 31 of 1940!.

[David Sparkes]

Thankyou Phil,

I'd thought of 'conduit' but then couldn't find anything special in my reference books, so convinced myself that they must use BSP, as conduit is pipe, isn't it? Obviously not.

Following your lead I've found reference to the BS31 relating to conduit threads, but nothing (yet) on details of Imperial Conduit threads. Modern references seems to be towards either Metric or Pg threads, and on those the 16TPI don't match the 1" OD.

Thanks again, I'll pass the message on, although I've been told not to expect any response before the weekend.

Cheers

Edit; For interest see https://ssl.perfora.net/metricshop.com/tech/thddat11.htm

I'm not sure why it's classed as a secure page (https).

[Phil Hancock]

Its only 1" diameter 16tpi to normal whitworth thread form. Conduit is a thin wall and the size is based on the od, normal pipe is sized on its bore and has a lot thicker wall hence the slightly coarser thread.