Sump plug thread

[Gadgetman]

Is the 1600 sump plug thread 3/8 bsp? I’m looking for a magnetic sump plug to catch all the running in ferrous fuzz !

[Pete Lewis]

all small chassis 4 cyl and 6 cyl  use the same plugs   in sump gearbox and diff.

its  a 3/8npt x 18tpi  see the other thread with links to these with magnets

the type with a hex head and seal washer do really need a face to seal against  vs the taper seal of the originals

 

[Gadgetman]

3 hours ago, Pete Lewis said:

all small chassis 4 cyl and 6 cyl  use the same plugs   in sump gearbox and diff.

its  a 3/8npt x 18tpi  see the other thread with links to these with magnets

the type with a hex head and seal washer do really need a face to seal against  vs the taper seal of the originals

 

Thanks Pete.

I did buy 2 magnetic 3/8 NPT sump plugs from Quilers and they only go in 2 turns, whereas the old sump plug goes in 4 full turns. I'll try getting some from somewhere else. I assumed the sump was BSP as they didnt fit!

[Pete Lewis]

there are a few out here where things dont fit 

you never know if in previous life ownership the sump collar has been repaired /retapped 

Pete

[Gadgetman]

Pete.

I've this afternoon managed to borrow a 3/8 NPT  tap and it goes into the sump threads  fine so the magnetic plugs I've got cant be the right thread.

Time to order another magnetic plug!

[Pete Lewis]

you can compare these  top is NPT  and lower is BSP  note some small differences in dia and pitch

 

 

Standard sizes[edit]

 

 

American Society of Mechanical Engineers National Pipe Thread Taper (NPT)^[6]

Nominal pipe size	Thread density	Thread pitch		Hand-tight engagement[7]			Effective thread[7]			Overall length[7]	Actual outside diameter, OD		Tap drill
				Length	Turns	Diameter	Length	Turns	Diameter
inch	inch−1	inch	mm	inch		inch	inch		inch	inch	inch	mm	inch	mm
1⁄16	27	0.03703704	0.9407	0.1600	4.32	0.28118	0.2611	7.05	0.2875	0.3896	0.313	7.950
1⁄8	27	0.03703704	0.9407	0.1615	4.36	0.37360	0.2639	7.13	0.38000	0.3924	0.405	10.287	0.339	8.6106
1⁄4	18	0.05555555	1.4111	0.2278	4.10	0.49163	0.4018	7.23	0.50250	0.5946	0.540	13.716	7⁄16	11.113
3⁄8	18	0.05555555	1.4111	0.2400	4.32	0.62701	0.4078	7.34	0.63750	0.6006	0.675	17.145	37⁄64	14.684
1⁄2	14	0.07142857	1.8143	0.3200	4.48	0.77843	0.5337	7.47	0.79178	0.7815	0.840	21.3360	23⁄32	18.2563
3⁄4	14	0.07142857	1.8143	0.3390	4.75	0.98887	0.5457	7.64	1.00178	0.7935	1.050	26.6700	59⁄64	23.4156
1	11 1⁄2	0.08695652	2.2087	0.4000	4.60	1.23863	0.6828	7.85	1.25631	0.9845	1.315	33.4010	1 5⁄32	29.3688
1 1⁄4	11 1⁄2	0.08695652	2.2087	0.4200	4.83	1.58338	0.7068	8.13	1.60131	1.0085	1.660	42.1640	1 1⁄2	38.1000
1 1⁄2	11 1⁄2	0.08695652	2.2087	0.4200	4.83	1.82234	0.7235	8.32	1.84131	1.0252	1.900	48.2600	1 47⁄64	44.0531
2	11 1⁄2	0.08695652	2.2087	0.4360	5.01	2.29627	0.7565	8.70	2.31630	1.0582	2.375	60.3250	2 7⁄32	56.3563

 

 

this is BSP

G / R size	Thread density (TPI)	Thread pitch	Major diameter		Minor diameter		Gauge length		Tapping drill
									R 95%	G 80%
(in)	(in−1)	(mm)	(in)	(mm)	(in)	(mm)	(in)	(mm)	(mm)	(mm)
1⁄16	28	0.907	0.3041	7.723	0.2583	6.561	5⁄32	4.0	6.6	6.8
1⁄8	28	0.907	0.3830	9.728	0.3372	8.566	5⁄32	4.0	8.6	8.8
1⁄4	19	1.337	0.5180	13.157	0.4506	11.445	0.2367	6.0	11.5	11.8
3⁄8	19	1.337	0.6560	16.662	0.5886	14.950	1⁄4	6.4	15.0	15.3
1⁄2	14	1.814	0.8250	20.955	0.7335	18.631	0.3214	8.2	18.7	19.1
5⁄8	14	1.814	0.9020	22.911	0.8105	20.587	0.3214	8.2	20.7	21.1
3⁄4	14	1.814	1.0410	26.441	0.9495	24.117	3⁄8	9.5	24.2	24.6

 

[Gadgetman]

Thanks Pete, that ties up as the old sump plug easily went in 4 turns and the NPT chart says 4.32 to hand tight

[Gadgetman]

Hmmm after buying another magnetic sump plug from the e bay seller it turns outs its Quillers selling them so ive yet another supposedly 3/8 bsp  one from them that doesn’t fit. It goes in 2 turns then locks up! It doesn’t have enough taper to go in further it’s an almost a parallel thread on the magnetic sump plug provided! Where’s my existing non magnetic one has a definite taper. 

Anyone bought one that actually fits s screws in at least 4 turns??

[Pete Lewis]

https://www.ebay.co.uk/itm/MAGNETIC-Triumph-MG-Sump-Diff-Gearbox-Drain-Filler-Plug-114774-15560-/222983483896

Copied  from  the  diff oil  post 

Pete

[Gadgetman]

Pete

thats the one I bought, it’s Quillers selling it. 

[Nigel Clark]

1 hour ago, Gadgetman said:

Pete

thats the one I bought, it’s Quillers selling it. 

+1, I bought one of those recently. The thread seems very tight in the sump. I put it in with a couple of turns of plumbers ptfe tape to seal the threads. Seems okay so far.

Nigel

[Mad4classics]

It seems many suppliers are selling BSP sump plugs, do they just see 3/8 pipe and assume BSP will fit! As Pete's data above NPT is correct; BSP has a different TPI and will not screw in very far or seal properly.

David

[Pete Lewis]

To,check  can you  take the gearbox filler out and try it in the  sump  it should  fit ??  Just to prove the sump tapping is unmolested

Pete

[KevinR]

The picture of the one on the Ebay advert looks incorrect - besides probably being a BSP thread rather than an NPT thread, there just isn't enough of a taper on in.

[Badwolf]

17 hours ago, Pete Lewis said:

https://www.ebay.co.uk/itm/MAGNETIC-Triumph-MG-Sump-Diff-Gearbox-Drain-Filler-Plug-114774-15560-/222983483896

Copied  from  the  diff oil  post 

Pete

I bought one last week. Can't find the one I bought from JP to compare. Also I don't want to drop the oil in the sump to try it at the moment, as the oil has only done a few hundred miles, plus if its still the wrong thread, my old plug may then be too far gone to go back in.

[Pete Lewis]

Weld a big nut to the old plug !!!

Pete

[Badwolf]

Pete - Thanks for the tip, but remember, I don't weld and even with the research on adhesives, I doubt that anything that I have tested would take that amount of torque.

[Badwolf]

... however, a hex nut, filed out to match the 'squarish' head of the old mangled plug, then bonded and hammered onto the old plug head might just work. One for consideration at the next oil change. Plus drill out the plug inside and fit a magnet.... maybe not.

[Pete Lewis]

They dont need to be that tight  sump plugs and gorrilla hands are a no no!!!

A hand  tight nip without raising blood pressure is all ot takes 

Pete

[Badwolf]

To further the discussion on the sump plugs available, I have found the sump plug that I bought from JP and this is a photo of the two sump plugs together...

.. the one on the left is from the fleabay web-link above, the one on the right from JP. Both are sold as fitting a MkIV Spitfire/Herald 13/60 (114774/155660)

The external diameter of the Fb one on the first thread is 0.592inches the last thread is 0.668inches the thread length is 0.475inches

The external diameter of the JP one on the first thread is 0.653inches the last thread is also 0.653inches the thread length is 0.322inches.

Unfortunately my caliper is not fine enough to measure the internal thread diameter.

Kevin is probably correct as the taper does is not sufficient compared with the original

[KevinR]

Just measured a genuine sump plug from a spare sump I have lying around in the workshop.

Diameter of 1st thread is 0.614"

Diameter of last thread is 0.685"

The threaded section is 0.5" long

It takes just over 3 1/2 turns to get it to lock finger tight in the sump.

I've also put a 3/8 NPT tap through the hole using finger grip only - also tried a 3/8 BSP tap and it bound up after a couple of turns.

My money is on the ones currently for sale being BSP rather than NPT thread.

 

Next time I need a magnetic one I'll get a magnet and drill a hole in an old plug - certainly wouldn't trust the one from Quillers.

[Badwolf]

Thanks Kevin. Incidentally why is it classed as 3/8th NPT when its over 1/2 in diameter? I'm sure that I read somwthing similar about whitworth threads but can't find the posts.

[Pete Lewis]

the  above   charts give all the relevant sizes the major diameters all relate back to the pipe internal and external diameters  all dream up by someone with a sense of humour !!

pete

 

 

 

[Gadgetman]

On 04/10/2019 at 21:15, Pete Lewis said:

To,check  can you  take the gearbox filler out and try it in the  sump  it should  fit ??  Just to prove the sump tapping is unmolested

Pete

Pete

ive tried the fleabay / Quillers one in my spare gearbox and I get the same result. It only goes in 2 turns 

 

[Unkel Kunkel]

- I am not an engineer, ready to be advised if wrong, but my basic  understanding  is that old  Mr Joseph Whitworth in the mid 19C  gave us the  Whitworth thread based on a 55 degree pitch and radiused “ trough” 

The British Standard Pipe thread = BSP is based on that.

In 2 forms:

- a parallel thread   “British Standard Pipe Parallel” =BSPP

-a tapered thread  “British Standard Pipe Tapered” = BSPT

However, In North America, a different system was adopted based on a 60 degree pitch and sharp “troughs” ( not the right engineering term,I know)

This was, and  still is their “imperial i.e. non- metric standard,  for pipe threads.

This is  “National Pipe Thread” = NPT.

Being a taper thread, the T is also taken as being Tapered.

In addition to North America, tap and die sets, from elsewhere-  from Taiwan   for example,  will have the American NPT taps, not BSP.

 

1.I can’t think British cars were  ever been equipped with  NPT  threads,

They will have been BSP - whether parallel or tapered.

I.BSP and NTP are not compatible, though probably can be “made “ to fit.

( look at Pete’s charts )

2.A taper thread is designed so that as it is tightened  until the the threads  start to seal against each other  -  without the use of  a sealing washer, tape or anything, and this should be achievable with very little torque.

3.A parallel thread set up  needs a sealing washer of some sort or something to seal the threads as  there isn’t the thread -sealing of the taper system.

 

What you need is  old Joe Whitworth’s  British   BSP .... not NTP!