Suitable water temp sender for Morris Marina thermostat housing

[IslipMinor]

As above, NPT and NPTF (F= Fuel) is the US pipe thread standard, and BSP(T) (tapered) is the UK and ISO standard. Although some sizes have the same TPI, they are not interchangeable. Both are used as parallel threads (NP and BSP) and taper threads (NPT and BSPT)

There was a debate on this forum some while ago while I was putting the bolt/screw thread table together that is now on this board, that the oil pressure switch thread in the block was identified as 1/8" NPT and not 1/8" BSPT. No idea why the 'British' Motor Corporation would use a US thread, even when if the A-Series engine came originally from Austin? But they did!

The table below shows the TPI and tapping drill sizes for a range of pipe threads. The 'Thread Size' refers to the nominal bore diameter of pipe, rather than the normal convention of thread OD (outside diameter).

BSP and NPT Thread Sizes.jpg (64.1 KiB) Viewed 1086 times

[JOWETTJAVELIN]

A photo of the head with blanking plug shown and details of the head casting number would be appreciated.

Here you go, they mean nothing to me. The engine number starts 8G though it looks like BC in the photo.

[philthehill]

You appear to have a recon/rebuilt 948cc engine fitted with a 1098cc 12G202 cylinder head.

The engine number is typical for a factory recon/rebuilt engine,

[jagnut66]

The only way round it is to make/use an adapter to suit either the capillary type transmitters or the electrical type transmitter.
When the early capillary type transmitter is fitted to the head there has to be a another 5/8" UNF male to 1/2"BSP male adapter screwed into the head to allow the 1/2" BSP female nut that secures the capillary tube bulb to be attached.
Later capillary type transmitters when fitting to the head will also need adapter https://www.moss-europe.co.uk/adaptor-t ... soc=506734
As the Marina Thermostat housing thread is 1/2" BSP a double ended 15mm pipe joiner can be screwed into the housing which will accept the early capillary tube transmitter and securing nut.
When fitting the capillary tube - the clearance between capillary bulb and thermostat must be checked.

Thanks Phil, I have now ordered one from Moss. If I understand what you are saying correctly, in simple terms, there needs to be space between the bottom of the sender unit and the thermostat.
Best wishes,
Mike.

[philthehill]

Correct. If there is no space the thermostat cannot open and the engine will overheat.

The sequence of fitting a late type capillary tube sender is:-

1. Fit modified brass blanking plug into Marina thermostat housing.

2. Fit MOSS adapter into modified brass blanking plug.

3. Fit Capillary tube sender into MOSS adapter.

Sequence of fitting electrical transmitter is:-

1. Fit modified brass blanking plug into Marina thermostat housing.

2. Fit electrical transmitter into modified blanking plug.

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Make sure that the thread is in the absolute centre of the brass blanking plug as there is little metal between the male and female threads even when the female thread is central

I would suggest that when modifying the brass blanking plug for the electrical transmitter it is not drilled and taped right through but the drilling and tapping is stopped short of the bottom of the plug to provide a seat and seal. Drill a pilot hole right through for the transmitter bulb.

[jagnut66]

The standard temp gauge hole/thread in the head is 5/8" UNF and the hole/thread in the Marina thermostat housing is 1/2" BSP (13/16").
The hole in the head has a seat for the transmitter to seat and seal against. The Marina thermostat housing does not have a seat which may make it difficult to seal the transmitter in the housing.
The only way round it is to make/use an adapter to suit either the capillary type transmitters or the electrical type transmitter.
When the early capillary type transmitter is fitted to the head there has to be a another 5/8" UNF male to 1/2"BSP male adapter screwed into the head to allow the 1/2" BSP female nut that secures the capillary tube bulb to be attached.
Later capillary type transmitters when fitting to the head will also need adapter
https://www.moss-europe.co.uk/adaptor-t ... soc=506734
As the Marina Thermostat housing thread is 1/2" BSP a double ended 15mm pipe joiner can be screwed into the housing which will accept the early capillary tube transmitter and securing nut.
When fitting the capillary tube - the clearance between capillary bulb and thermostat must be checked.

Hi Phil,
What size is the correct tap and dye for the hole / the thread on adapter?
Do you have a link to one?
My largest one is too small, I will buy them and add them to my set.
Many thanks,
Mike.

[philthehill]

If you fit the modified plug to the Marina thermostat to accommodate the electrical type transmitter and the later (male) type capillary transmitter you will require a 5/8" UNF tap.

If you want to fit an early type capillary type transmitter you will need a 1/2" BSP tap as to allow the double ended 1/2" BSP adapter to screw into the Marina thermostat housing.

[jagnut66]

Thanks Phil.

[jagnut66]

Hi,
One good secondhand tap later and I have the a water temp sensor mounting that is ready to fit.
The sensor is only 'fingertight' at present, I will remove it whilst all the fitting work is going on, so as not to damage it.
Though it should be well clear of the thermostat.
Many thanks for the advice.
Best wishes,
Mike.

[philthehill]

Well done.

To get that transmitter bulb a bit more into the coolant flow I would suggest machining the hexagon head (which is 6mm deep) off the adapter plug and using Loctite lock and seal join the brass adapter plug and the transmitter holder together. You will still have plenty clearance between the bottom of the transmitter and the thermostat.

Can you please post the part number of the temp gauge transmitter you are using and source of supply.

An observation:-
The brass adapter plug does not appear to fit inside the raised lip of the thermostat housing filler plug hole. The original plastic filler plug does fit inside and is 29.3mm O.D. where as the brass plug is 31.5mm. If the brass plug is not able to fit inside the raised lip - sealing of the hole may not be possible. The rubber sealing ring must be compressed to do its job.

Phil

[jagnut66]

Hi Phil,
As requested here is a link to the sensor:

https://www.ebay.co.uk/itm/Morris-Marin ... 2749.l2649

You are right about the brass filler plug, it does sit on top of rather than into and although it is tight water always finds a way.........
Any suggestions?
Best wishes,
Mike.

[philthehill]

Reduce the O.D. of the brass adapter/plug to 29.3mm. Reducing the O.D can be done using a file.
The adapter plug must be able to fit inside the raised lip so as to be able to press down on the rubber 'O' ring which is the means of sealing the hole.
The lip around the hole must be retained as it keeps the 'O' ring in place and stops it being squashed out when the adapter/plug is tightened.
I am having to do exactly the same on a recently purchased brass plug which will replace the not so perfect original plastic plug.

Phil

[jagnut66]

Well, I preempted Phil a little here, as I guessed he was going to say get the grinder out (rather than file) which is what I did. Though I got my files out also.
I bit the bullet and using my tap as a spindle and with the grinder secured in the vice, I turned the plug until enough had been taken off for it to fit inside the lip of the housing. I was being very careful not to take too much because, as Phil says, you need a retainer for the 'O' ring.
Then holding the housing in the vice and with Threadloc applied, I used the nut section on top of the brass bung to wind it in as tight as possible. I hope it's enough, as the next thing I did was to grind off this section and file it flat. I then re-tapped the hole and refitted the adapter, again using Threadloc and a fibre washer. The sensor is just finger tight at present, as I will remove that whilst fitting the housing to the head.
I'm attaching the pictures below to show that this was done in fairly basic conditions outside (concrete base goes down on Wednesday -- fingers crossed). I don't even have a tap wrench to fit my 5/8" tap at present, so I used a brake pipe spanner, as it has a square hole. You just need to take care to start the tap square in the hole.
The main reason for showing my basic working conditions though is to encourage others who might think they 'don't have the skills'.
Everything I have learnt over the years has either been self taught or done acting on the advice of others (and mentally noted). I am just an amateur, I have no special skills or qualifications, the main things you need are a willingness to try and to persevere. Don't give up (sometimes easier said than done) and don't be afraid to try something.
My self made rear wiring loom may not please the purists and the route I took may be criticised by some but it fixed the problem, was an interesting learning curve and once it's all back together no one will notice anything different.
I'm now going to renew the front loom, with a bought loom this time, as I want this to look right and it can be seen. The idea fills me with trepidation, especially as I need the car mobile by Wednesday again but I will go ahead (with crossed fingers!! ).
So for all my fellow amateurs out there, go on give it a go and don't be afraid of taking on a less than perfect Morris Minor.
Best wishes,
Mike.

PS: You can never have enough tools / spanners, so if someone offers you some they don't want anymore, bite their hands off!