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MG Midget and Sprite Technical - Bypass hose adaptor thread

The bypass house adaptor that is threaded into the lower face of my 12G295 cylinder head has all but disintigrated making it impossible to unscrew. I suspect that I will need to drill it out. Does anyone know what the thread size is of the adaptor that screws in here?
I'm probably going to need to buy a tap to clean-up afterwards.
Simon Wood

Don't worry, found it. Would appear to be 5/8 UNS 16TPI
Simon Wood

I can’t remember the actual thread size, but it’s the same as the temperature sender IIRC. There is a blanking plug that fits the head on early A+ engines in place of the bypass take-off, and I used the same plug in the radiator boss.

There was a thread last year about the thread size of the temp sender, so there should be info in the archives.
Dave O'Neill 2

If you’d found it five minutes earlier, you could have saved me some typing LOL
Dave O'Neill 2

Simon

Info here, including alternative bypass nose adapter: http://www.minispares.com/product/classic/12A2075.aspx

According to this link: 'This is the longer type cylinder head adaptor tube which allows fitment of the by pass hose without removing the head. The shortened hose slides up the tube and then back down on the water pump tube. Frequently rusted on old heads and not even there on newer heads. These are 5/8" x 16tpi "whitworth fine" thread and if the thread in the head is badly corroded and you cannot find the correct original tap some owners have used 5/8" x 16tpi unf thread tap and fitted 12H1405MS tube originally used for inlet manifold servo take offs.'

http://www.minispares.com/product/Classic/Exhaust_and_manifold/Inlet/Inlet/12H1405MS.aspx?110202&ReturnUrl=/search/classic/12H1405MS.aspxBack%20to%20search


Perhaps you may not need to unscrew this and fit replacement bypass hose?

Bypass hose options: http://www.minispares.com/product/Classic/Engine/Cylinder_heads/Valves_accessories/12A1093MS.aspx?100410&ReturnUrl=/shop/classic/engine.aspxBack%20to%20shop

http://www.minispares.com/product/Classic/Engine/Cylinder_heads/Head_components/GZA2083.aspx?100402&ReturnUrl=/product/Classic/Engine/Cylinder_heads/Valves_accessories/12A1093MS.aspxBack%20to

http://www.minispares.com/product/Classic/Cooling_heating/Water/Hoses_fixings/C-GZA2083.aspx?070302&ReturnUrl=/product/Classic/Engine/Cylinder_heads/Head_components/GZA2083.aspxBack%20to

Cheers
Mike





M Wood

As I mentioned before the minispares page in the first link above is wrong in that it mentions both threads as 16 TPI where 5/8" BSF is 14 TPI and 5/8" UNF is 18 TPI. I did email them and got a reply saying they would look into the problem but obviously haven't done anything to correct the issue.
David Billington

Simon,
if it's not too late -

I bought the mini spares 'BY PASS HOSE ADAPTOR, LONG LATER TYPE ON CYL HEAD' (but was unable to use it) and it's quite long (1" below collar to threads) so this gets it very close to the water pump bypass pipe making fitting even the thinner walled concertina type hose awkward (plus on mine the two pipes were slightly offset) unless the head is off so go for the long lasting silicone hose as you won't want to struggle fitting a later replacement.

Unless things have improved, the last Kevlar hose I bought wasn't very good.

I also bought, not from min spares but local, a thicker walled, 4-ply (blue) silicone bypass hose (that would need the head off to fit to the long hose adapter) plus Kale clips.

Let me know if they're of interest to you - £4 plus P&P at cost.

first and last name at bt internet dot com
Nigel Atkins

Nigel, thanks for your kind offer. I have all of the parts needed and yes, I had thought that the adapter looked a bit too long. No bother, I will shorten it.
I have known about the issue for a while and have to sort out a slight oil weep that seems to be originating at the head gasket near to the heater tap. Just wanted to make sure that I have all of my ducks lined up before whipping the head off.
Simon Wood

Simon,
if you're taking the head off you don't need to shorten the adapter, the slots in the end of it will also be useful for fitting. Use silicone hose for fit and forget. You can put the hose on the water pump and offer up the head and adapter. Take care which direction you fit the jubilee clips, so that you can get at them to tighten them if required, with everything fitted in the engine bay that will usually get in the way on a running engine bay.

The normal length adapter means the clamp of the jubilee clip clamp sits almost off the end of the adapter so you have to be careful not to over-tigthen or the clip goes off at an angle because of the position of the clamp and squashes out the hose above the clip causing a weep (guess how I know).

With the head on, even with the rad out, getting the hose on and clamp in a good position to sit well and get at later requires just a little attention.
Nigel Atkins

This thread was discussed between 15/09/2018 and 16/09/2018

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