Cylinder head water pump by-pass pipe thread

[GeoffCreamer]

Does anyone know the thread detail of the cylinder head tapping that takes the screw in by-pass pipe stub? I have just removed my old rusty one with great difficulty and the new one only screws in by 1 turn then locks solid. I know that the pipe has a taper thread but I want to run a tap into the head thread to clear of rust. It doesnt seem to be BSPT as expected. Any ideas?
Geoff

[bmcecosse]

I'm really not sure....something tells me it's the same as the tapping for a servo take-off in the manifold - and a 5/8" thread - but whether UNF or UNC - I'm not sure, although I'm leaning towards the UNF... I'm not at all convinced it's a taper thread.

[philthehill]

The thread is 5/8" x 18 TPI UNF.
It is a straight/parallel thread.
If you do not have the required tap they are available from http://www.engineering-supplies.com product code No: ES-3426 @ £12.40 plus VAT.
I source all of my tap and die requirements from them and they provide a very good service.

See my revised posting below.

[bmcecosse]

Thanks Phil - thought it rang a bell!

[Declan_Burns]

This was discussed in great detail some time ago.
See:
http://www.mmoc.org.uk/viewtopic.php?f= ... S&start=15

Regards
Declan

[bmcecosse]

Indeed Declan....but my old memory is not as good as it used to be.... actually, it's always been pretty rubbish...

[philthehill]

Declan
The blanking plugs purchased by myself to block off the bypass hose adapter hole in the cylinder heads head have been (and still are) advertised and supplied with 5/8" UNF threads and they were the ones that I took the dimensions and TPI from as I do not have an original bypass hose adapter to hand to check against.
These 5/8" x 18 TPI UNF blanking plugs are the same thread as the inlet manifold take off pipe and I have checked those threads against each other and they are the same.
I have now found some NOS bypass hose adapter hole blanking plugs and the thread is as you say 5/8" x 16 TPI UNS.

Geoff please note and ignore my post above stating that the thread is 5" x 18 TPI UNF.

As regards the correct tap as requested by Geoff unless you can find one on 'e' bay at a reasonable price the tap is available at a cost of between £70 - £100 per tap. No small amount.

[bmcecosse]

I do think the UNF thread is correct - it's been discussed often on various Mini forums - and the 'special thread' is certainly in the crank - but NOT in the head or inlet manifold. Can you try one of your plugs in an inlet manifold Phil ??

[bmcecosse]

I 'consulted' with Adrian (A C) Dodd - renowned Mini engine expert - and he is confident it is 5/8 UNF - he fits the standard 5/8 UNF bypass inserts without any problem and has never had a leaker.

[philthehill]

Roy
I have just tried a 5/8" x 18 TPI UNF die on a BMC PCV take off adapter Pt No: 12H1405 and the 5/8" x 18 TPI UNF screws on easily without trying to cut a new thread.
The NOS bypass hose blanking plugs I have found have a totally different thread i.e. 5/8" x 16 TPI UNS. I have placed a 5/8" x 16 TPI UNS 'bottom' tap against the threads and they are the same.
If I remember correctly those NOS blanking plugs were supplied by Oselli many years ago for the purpose of blanking off the bypass hose and one was fitted to my then installed Oselli modified 940 head.
Was there a change over in the threads of the bypass hose adapter at some time that reflects the current advert for 5/8" x 18 TPI UNF bypass adapter blanking plugs?
I have just tried to remove the bypass hose adapter from a late 940 head I had on the shelf to check the thread but as expected the adapter will not budge - so that will have to be now drilled out and either a new bypass adapter or the hole blanked off before going back into use.

[bmcecosse]

Ah well, AC does mention that most of his work is on late model 940 heads. But it's hard to imagine that even MG/Rover would change the thread of such a small component - just for the hell of it!

[GeoffCreamer]

Thanks for the responses and the old threads. I just tried a 5/8 x 14 BSF tap in an old head and the fitting fits well enough. I agree that the ESM stub measured 16 TPI and a few thou smaller OD. It was definitely tapered too but I am not sure if this is a poorly made part or a genuinely odd thread. I also emailed ESM and they said it is 5/8 UNS which was new to me but is listed on the web too. It is a 60 deg form but still 14 TPI and same OD as BSF. But given that I have a BSF tap I decided to give it a go. I have just done the restored head and the fitting is good and tight and screws down most of the thread. A bit of thread sealant should be job done.
Many thanks, Geoff

[bmcecosse]

As long as it doesn't leak!