Engine heat for the calorifier

[Theo]

I am now onto the plumbing and want to use the engine heat for heating the water.

 

Theodora's engine is a BMC 1.5.

 

Item: one bottom hose with side arm for the return from the calorifier. I found something that I think will do on a visit to Parkers on Abbey Lane. It is not the correct hose for the job but I am reasonably confident that I will be able to cut it down to fit.

 

Item: One threaded spigot to replace the threaded plug from the top of the engine block. Parkers could not help but I needed to go to the plumbers' merchant anyway so I asked there. They had what looked just the job and I returned to the boat in a high state of delight. What they had sold me was a 5/8" BSP brass fitting with a compression joint for the tube that I was to attach. I had checked it for size and it seemed perfect. The plug that I had removed from the engine fitted the same female attachement that the brass fitting that I had bought fitted into.

 

My delight was short lived because the brass fitting was just a fraction too big. I tried some judicious persuasion but half an hour's trying convinced me that it was not going to work.

 

Does anyone know what size I really need and where I could get that which I need?

 

In hopes

 

Nick

[Big Steve]

I'm not sure what size you need, but there are two types of BSP thread, BSPP (British Standard Pipe Parallel) and BSPT (.....Tapered) so you might need the other one, if you get my drift. The BSPP male will only fit a BSPP female, but the BSPT male will fit both BSPP and BSPT females. This would explain the conundrum at the plumbers. If the fitting he's sold you is BSPP it would fit into a BSPP hole. The one on your engine is BSPT. So the plug you took out (BSPT)would fit into the female BSPP the plumber had, which would also accept the bit he was selling you, but the fitting wouldn't fit into the BSPT hole in your engine.

 

BSPT are sometimes more readily available in malleable iron.

 

Does that make sense? I'm totally bloody confused now, where's the whiskey?

 

There are also NPSM connectors used for compressed air, which look similar to BSP but are not compatable, but I doubt very much if these threads will have been used on a BMC engine.

 

PS I'll see if I've got one in the shed tomorrow, I'll let you know.

 

Steve

[Theo]

I'm not sure what size you need, but there are two types of BSP thread, BSPP (British Standard Pipe Parallel) and BSPT (.....Tapered) so you might need the other one, if you get my drift. The BSPP male will only fit a BSPP female, but the BSPT male will fit both BSPP and BSPT females. This would explain the conundrum at the plumbers. If the fitting he's sold you is BSPP it would fit into a BSPP hole. The one on your engine is BSPT. So the plug you took out (BSPT)would fit into the female BSPP the plumber had, which would also accept the bit he was selling you, but the fitting wouldn't fit into the BSPT hole in your engine.

 

BSPT are sometimes more readily available in malleable iron.

 

Does that make sense? I'm totally bloody confused now, where's the whiskey?

 

There are also NPSM connectors used for compressed air, which look similar to BSP but are not compatable, but I doubt very much if these threads will have been used on a BMC engine.

 

PS I'll see if I've got one in the shed tomorrow, I'll let you know.

 

Steve

 

Is the fact that I could not even get the fitting started in the thread relevant?

 

I off to the boat today so I will get another fitting and see if I have any more success.

 

Nick

[Big Steve]

I had checked it for size and it seemed perfect. The plug that I had removed from the engine fitted the same female attachement that the brass fitting that I had bought fitted into.

 

Having slept on it, from this statement, I'm convinced that what you have in the block is a female BSPT thread, it's the only way this could happen. I'm just about to go in my shed to check me bits.

[Big Steve]

Now I've had a rummage. Baffled. I have tapered and parallel fittings and they all fit into each other. Looking at the spec of these threads the 5/8 has a diameter of .902", the 1/2 a diameter of .825", both with 14 TPI. Are you sure it's not 1/2 BSP that you should have? Can you measure the diameter of the plug from the block and the TPI? If you let me have that info I might be able to work out what it is.

 

I have here in my sweaty paw a brass 1/2" BSPT to 15mm male connector . If you e mail me your address I'll send it you. Free. ( I don't have any 5/8 stuff)

[Reginald]

Hi It should be a 5/8 UNF. You can get an adaptor from AMC in Preston for about a £5.00

[Theo]

Hi It should be a 5/8 UNF. You can get an adaptor from AMC in Preston for about a £5.00

 

All useful stuff this!

 

Reginald. Do you know this as a fact? If you do I will send off for the adaptor real soon now.

 

BTW what does it adapt to?

 

Nick

[Reginald]

All useful stuff this!

 

Reginald. Do you know this as a fact? If you do I will send off for the adaptor real soon now.

 

BTW what does it adapt to?

 

Nick

 

 

I had a braas adaptor snap(corrrode) off in the connection. I asked Shaun at AMC is reply

 

 

 

Thank you for your enquiry.

 

The thread size for the heater connection should be 5/8unf.

 

We have hose connectors available in stock to suit ½” hose @ £4.25 GBP each + vat

 

I drilled it out and cleaned the thread with the 5/8 unf tap I borrowed.

 

 

The bad news was that it was in July 2004 so it might have gone up a bit.

[Big Steve]

If it is 5/8 UNF, and personally I don't have a clue, how did the plug removed from the block fit into a 5/8 female BSP socket? 5/8 Bsp is .902" dia, 5/8 UNF is .625" dia, no way will it fit.

[Reginald]

The fitting possibley fitted due to BSP having a 30% taper. The .902" is the maximum diameter of the taper. I would think it would seem strangr for a engine manufactuer to mix threads on a engine block and use BSP ( A plumbing Standard) as well as UNF. below is an cutting from the history of BMC

 

The last M.G. to use such threads was the TF1500 in 1955. Such nuts and bolts have British BSW/BSF head sizes, so that the average British DIY owner or motor mechanics tool kit could still be used, but with these odd metric threads. From then on, starting with the M.G. 'Z' Magnette in 1953, Austin engines were used under the umbrella of the British Motor Corporation, or BMC for short. These BMC engines used American based Unified Fine (UNF) and course (UNC) threads, ( ANF & ANC in the USA,) in the 'A','B' and 'C' series M.G. used. Such nuts and bolt heads had to be used with spanners that are termed "A/F", indicating the distance Across the Flats, a common size for instance, being 1/2" AF. Later still, standardised ISO metric sizes took over with the 'A' Plus, 'O','R','S', and 'K' series engines of Austin/Rover.

 

this is the link to the article

 

http://www.mgcars.org.uk/engine/mgenginehistory.rtf

[Big Steve]

Even allowing for the taper ( which is 1^o 47', not 30^o), it's only a few thou. it wouldn't be anywhere near.

 

Re threads on British cars though, I recently sold a 1996 Landrover Discovery. It had a 1/2BSP fitting in the head and in the radiator. They were a plastic plugs, one cracked, letting the water out. I replaced it with a standard central heating radiator plug.

[Theo]

I have brought the plug home and got out the vernier calipers:

 

Thread diameter = 15.5mm = 0.610"

Across flats = 18.7mm = 0.736"

 

Using 25.4 mm = 1"

 

That does not seem to match up. I have checked the zero error on the vernier.

 

I am now a little confused.

 

Nick

[Big Steve]

If it measure 15.5 mm thread diameter ie .610 inches, then it seems likely that it's UNF, it could easily have lost 15 thou due to corrosion. If it is UNF it should have 18 threads per inch. I'm very puzzled as to how the plug screwed into the same fitting has a 5/8 BSP though. Let's know how you get on.

[Theo]

If it measure 15.5 mm thread diameter ie .610 inches, then it seems likely that it's UNF, it could easily have lost 15 thou due to corrosion. If it is UNF it should have 18 threads per inch. I'm very puzzled as to how the plug screwed into the same fitting has a 5/8 BSP though. Let's know how you get on.

 

Would it have lost this much by corrosion? It seems to be in perfect condition. Perhaps since it only has some 7/16" for thread the general slackness might have allowed it to screw home without binding.

 

There is a gas fitting company not 100yards from the marina so I will trot along there on Tuesday to seen if they can help. Could you let me have contact details for AMC, please?

 

Nick

[Big Steve]

Is this them?

 

Hall Lane

Longton

Preston

Lancashire

PR4 5ZD

 

Tel: 01772 613003

Fax: 01772 616364

Email: sales@amcdiesel.co.uk

[Theo]

Is this them?

 

Hall Lane

Longton

Preston

Lancashire

PR4 5ZD

 

Tel: 01772 613003

Fax: 01772 616364

Email: sales@amcdiesel.co.uk

 

 

Thanks for the inforamtion, Steve.

 

I was leafing through that very excellent mag, WW, and happened upon an advertisement for Calcutt Boats, who profess to be specialists in BMC engines. Got on the phone to them and the chap at the end said that it was a cyclo thread and could not possibly have looked like a 5/8" BSP. I did not argue and ordered what he thought would be the right thing at an "inflated price" (his words).

 

I now await its arrival with eager anticipation.

 

Nick

Edited April 16, 2007 by Theo

[Big Steve]

Never heard of a cyclo thread, unless he means British Standard Cycle. Spec for that is .625" dia and 26 TPI, much finer than UNF. Can you measure between the crests of a few threads on the old plug? then we'll be able to work out the pitch and see what it really is.

[Big Steve]

My mate Pete, who's got one of these engines in his shed, says it's 3/8 BSPT, It should have 19 TPI and be .656" diameter. He says a malleable iron 3/8 x 2" nipple

is readily available from any decent plumbers merchant and should screw straight in, you just have to solder, push or screw something onto the other end as required. (nipple is the term used for a bit of pipe taper threaded at each end, I didn't know that)

 

Is other suggestion is to drill a hole down the plug you have removed and solder a bit of 15mm copper into it.

 

Keep me posted on progress, I'm fascinated to find out what it really is. ( doesn't take much to keep me amused)

[Theo]

My mate Pete, who's got one of these engines in his shed, says it's 3/8 BSPT, It should have 19 TPI and be .656" diameter. He says a malleable iron 3/8 x 2" nipple

is readily available from any decent plumbers merchant and should screw straight in, you just have to solder, push or screw something onto the other end as required. (nipple is the term used for a bit of pipe taper threaded at each end, I didn't know that)

 

Is other suggestion is to drill a hole down the plug you have removed and solder a bit of 15mm copper into it.

 

Keep me posted on progress, I'm fascinated to find out what it really is. ( doesn't take much to keep me amused)

 

I will keep you informed. I have been slaving away on Theodora all day. Plumbing. Two five way manifolds built and fitted with valves, one small leek on the calorifier repaired (I hope!) and ditto on the Mikuni.

 

I might wait for the post to arrive tomorrow to see if the adaptor appears.

 

Thanks

 

Nick

[Big Steve]

Theo, did you get this sorted?

 

Would like to know what a cyclo thread is!

[Reginald]

Is this them?

 

Hall Lane

Longton

Preston

Lancashire

PR4 5ZD

 

Tel: 01772 613003

Fax: 01772 616364

Email: sales@amcdiesel.co.uk

 

Yes they have all the bits to rebuild a BMC. They import then from Turkey under Thorneycroft or something like that. Always found then quick and friendly.

[Theo]

Theo, did you get this sorted?

 

Would like to know what a cyclo thread is!

 

I got the fitting from Calcutt but it was not a very good fit. Still don't know what the cyclo thread is.

 

It will only screw into the block about three turns and that will heaps of Nm. I phoned them and they convinced me that that was all the could suggest. They made comments about the cleanliness of the thread in the block (very clean) and I suggested that I get a tap to open up the threads a bit. They soon scotched this idea though saying that they could not source a tap of the correct thread. If you happen to have a Turkish made engine it is easier. On those the thread is 3/8"BSP.

 

In the end I decided to make do with the three turns and proceed with the work. AFAICT everything is OK and mechanically it all seems reasonably satisfactory.

 

Sorry that I cannot be more informative about the threads.

 

I wonder if it would be worthwhile drilling out the block and rethreading it with something that is more usual. Certainly it seemed to be very close to the 5/8"BSP that the plumbers gave me.

 

All the best

 

Nick

[Big Steve]

There is something very odd going on here. You measured the diameter of the plug at .610", that's no where near 5/8 BSP, but is close to 3/8 BSP. Have you tried a 3/8 BSP in it? My pal, who has an ancient genuine BMC engine assures me its 3/8 BSP.

 

If you measure the pitch of the thread with your trusty caliper it should be 1.34mm or .0526" if it's 3/8 BSP.

[John Orentas]

Some of the confusion here is that of outside and inside diameters of the pipe.

 

3/8" BSP = 19 threads per inch. Tapping size 15.25 mm. Major dia. = 0.656" 17mm Clearance.

[Theo]

There is something very odd going on here. You measured the diameter of the plug at .610", that's no where near 5/8 BSP, but is close to 3/8 BSP. Have you tried a 3/8 BSP in it? My pal, who has an ancient genuine BMC engine assures me its 3/8 BSP.

 

If you measure the pitch of the thread with your trusty caliper it should be 1.34mm or .0526" if it's 3/8 BSP.

 

I think I might leave it just where it is. It is *very* secure and migh tbe less so if I were to take it out. If something goes wrong and I need to take it out I will go down the 3/8" track.

 

Nick