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Jeff Martin
New User
Username: jeff_r_1

Post Number: 3
Registered: 07-2018
Posted on Wednesday, 23 October, 2019 - 08:27:   Edit PostDelete PostView Post/Check IP

As the title says, I twisted mine off trying to get it out of the head. Pretty sure it's BSPP (British Standard Parallel Pipe) thread, but I not sure of the size.
After looking at the minor and major diameter, I think it's designation is 3/8, that would make it 19 threads per inch.
I'll have to buy a tap to clean up the threads in the head after I dig out the broken tap.
Thanks
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Kelly Opfar
Frequent User
Username: kelly_opfar

Post Number: 241
Registered: 07-2004
Posted on Wednesday, 23 October, 2019 - 10:20:   Edit PostDelete PostView Post/Check IP

If you know the part number, you might be able to buy the original drawing from Hunt House:
https://archive.rrec.org.uk/search-result
They don't have everything and it's not free but I find it very useful at times.
Kelly

BritishToolWorks.com
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Jeff Martin
New User
Username: jeff_r_1

Post Number: 4
Registered: 07-2018
Posted on Thursday, 24 October, 2019 - 06:26:   Edit PostDelete PostView Post/Check IP

It's 1/2 inch BSPP thread. I also talked to a club member who has worked on many of these cars and he's threaded a new tap in there with 1/2 NPT, which is also 14 threads per inch _ so I could see that working.
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Norman Geeson
Unregistered guest
Posted From: 81.99.138.38
Posted on Wednesday, 23 October, 2019 - 20:59:   Edit PostDelete PostView Post/Check IP

Jeff

There are at least four different heater tap adaptors and at least two different heater / block taps in the early post war cars, viz:-RE18826, RE9888, RE8952, RE17083 adapters and RE5150 , RE 16535 block / heater taps

As you provide no data on the engine, chassis number or vehicle it is not possible to give you a definite answer, except to say these adaptors in the main are BSP to 20 tpi Whit form. With one exception of 24 tpi the others are 14 tpi BSP on the opposing side.

In addition to the above data one would also need to know into which cylinder pocket the adaptor / tap was screwed eg. No.2 or No.4.

Perhaps you could provide more data?

(Message approved by david_gore)
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Jeff Martin
New User
Username: jeff_r_1

Post Number: 5
Registered: 07-2018
Posted on Thursday, 24 October, 2019 - 07:48:   Edit PostDelete PostView Post/Check IP

Here's a photo, I did get enough of the old thread out of the head and I was able to measure it at 14 tpi, so part# RE16535, block/heater taps.
That equates to 1/2 inch BSPP.
The car is 1951 Bentley Mark VI standard body, B297LH, not that it matters.
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Norman Geeson
Unregistered guest
Posted From: 81.99.138.38
Posted on Thursday, 24 October, 2019 - 20:35:   Edit PostDelete PostView Post/Check IP

Jeff

My message should have read, was “screwed eg. No.2 or No.5” not “screwed eg. No.2 or No.4”.

For the record your heater tap (photo) appears to be a RE 5150 with two male couplings, one arrowed at ½ BSP 14 tpi, the other 7/8 Whitworth Form 20 tpi.

On later 4.25 ltr and early 4.5 ltr engines that heater tap was used with a RE 9888 adapter ½ BSP x ½ BSP, so the adapter could be left in the cylinder head without having to unscrew the heater tap from the alloy head.

The photo is NOT that of a RE 16535 as that particular tap has a “captured” female nut attached and it can only be used with a special adapter RE 17083.

This arrangement was only used from about May 1953 on R Type / Dawn engines to allow the tap to be mounted/ demounted without disturbing the front exhaust manifold.

(Message approved by david_gore)
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Jeff Martin
New User
Username: jeff_r_1

Post Number: 6
Registered: 07-2018
Posted on Saturday, 26 October, 2019 - 07:48:   Edit PostDelete PostView Post/Check IP

Thanks for all the info, very useful.
Any reason why the tap was moved from cylinder number 5 to 2, maybe better coolant flow to the heater being nearer to the water pump ?
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Norman Geeson
Unregistered guest
Posted From: 81.99.138.38
Posted on Monday, 28 October, 2019 - 20:50:   Edit PostDelete PostView Post/Check IP

Jeff

I think you may have guessed the reason for the re-siting of the heater supply point. I have not come across any comment on the subject in the archives.

However just about that time many changes took place in regard to cooling and heating, including the final positioning of the radiator grille shutters.

The introduction of the MKVI chassis Continental and the demister matrix positioning under the front wing may have accelerated the decision to reposition the heater take off points.

The introduction of the "commonised" Continental cylinder across the range in July / August 1953 might be another reason to tidy up cooling flows.

(Message approved by david_gore)
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MGlanville
Unregistered guest
Posted From: 118.211.223.178
Posted on Sunday, 10 November, 2019 - 08:34:   Edit PostDelete PostView Post/Check IP

May I ask a follow up question on the subject of heater taps? Mine is not leaking fortunately at No. 2, (cant remove in any event because of manifold) the adaptor to the block or at the tap to the adaptor. It leaks at the tap into the tappered body. I have removed and applied grinding paste etc....still leaks. What are the thoughts of a small grove top and bottom of the tap with a couple of nitrate O rings?

(Message approved by admin)
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Jeff Martin
New User
Username: jeff_r_1

Post Number: 8
Registered: 07-2018
Posted on Monday, 11 November, 2019 - 10:32:   Edit PostDelete PostView Post/Check IP

It would work if you could properly machine the grooves to take the O-Rings, but being a conical shaped thing, how would one lock into a lathe.

It would almost be impossible to file the grooves by hand and get the depths even enough for the O-Rings to seal.
I was planning on soldering mine in the open position and be done with it, I leave it open all year round anyway.
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Christopher Carnley
Unregistered guest
Posted From: 109.156.10.92
Posted on Sunday, 10 November, 2019 - 20:16:   Edit PostDelete PostView Post/Check IP

Is the captive back nut cracked?

(Message approved by david_gore)
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James Senior
New User
Username: jamess

Post Number: 11
Registered: 09-2016
Posted on Tuesday, 12 November, 2019 - 05:24:   Edit PostDelete PostView Post/Check IP

I managed to seal mine with Hylomar, which I believe was developed for the purpose.

http://hylomar.com/hylomar-product-range/gasket-jointing-compounds/
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paul hooper
Unregistered guest
Posted From: 122.58.90.161
Posted on Saturday, 22 February, 2020 - 14:27:   Edit PostDelete PostView Post/Check IP

To stop the petcock from leaking set the tap in the position you want ( open or closed) then support the petcock with one hand and tap the handle on the top with a hammer. This drives the taper shut.If you wish to change tap position a slight tap from underneath will release the taper.
A copper hammer is best as less damage to fitting. The pressure holding the taper closed is normally done by the spring washer underneath but these brake.
You can also add a washer between spring and nut to increase pressure to stop leaks. It does no harm to tap the petcock on the top, so don't be afraid.
CHEERS Paul Hooper

(Message approved by david_gore)

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