C/H plug insert size?

[CaliTrav]

Hi all,

When I was refurbishing my 940 cylinder head I removed an electric take off for a temp gauge, fitted where the plug would usually be, and also removed a very rusty and chewed up threaded insert. I'd assumed that this was part of the adaptor for the electrical take off.

However I've just come to fit the adaptor for the capillary take off and it's free floating in the hole with maybe 1-2mm of movement in every direction. The original blanking plug is the same.

So I'm guessing that threaded insert was original and probably a mistake to remove it!
Does anyone know the size for a replacement or have a link to buy one somewhere?

I've tried having a Google but it throws up the bypass hose and this is the other side (left, under the thermo housing next to spark plug 1)

[CaliTrav]

If it helps, the capillary type I'm currently using on a standard 1098 head has a male insert into the head (13/16 spanner size) and the capillary wire has a smaller male adaptor which fits the female side of the larger adaptor above (5/8 spanner size)

However the threaded insert into the head is smaller than the male insert for the wire and capillary tube.

The 5/8 capillary tube insert may screw directly into the head (also think it's too small) but without the extra space of the adaptor the sensor tube is too long.

Is this going to be a case of re-tapping the hole to a known size and getting a new threaded adaptor? I have a feeling there may not be a standard part...

[philthehill]

You require one of these:-

https://www.moss-europe.co.uk/adaptor-t ... ?assoc=143

[CaliTrav]

Love this forum! Thanks Phil.

Presumably that's 5/8 on both the male and female threads, which I think would work. I/D of the hole is 0.625" so 5/8...

[philthehill]

5/8" UNF threads in the head.

[CaliTrav]

The adaptor arrived today... And it's the same size as my old one, so that must be 5/8 to 5/8 too. It still has space around the edge, which makes me think that the head has been drilled/tapped out by someone in the past?

It is a small difference so I'm thinking that an 11/16 to 5/8 adaptor would work, but can only find them on American websites...

[philthehill]

There are two sizes/types of bulb/adapter for the capillary transmitter. You have the right one for the 'A' Series cylinder head.
I suspect that you have the earlier capillary bulb which requires the appropriate adapter.
This is the link to the earlier adapter which has a male/male thread:-
See the product information notes attached to the link.
https://www.holden.co.uk/p/adaptor_5_8_ ... e_gauges?s
See also link below for other adapters:-
https://www.holden.co.uk/search/070.044

[CaliTrav]

Thanks Phil.

I've just been down with my caliper - however I measure it, the hole in the cylinder head is definitely between 15.86 and 15.88mm - so allowing for my clumsy reading it's still 0.625" or 5/8 in size.

The male thread on the adaptor I've measured a few times around the diameter, with an average of 15.58mm, or 0.613". So that explains the gap.

The female connection on the other end fits onto the male of the bulb securing nut with no issues.

[philthehill]

The hole in the head should be 5/8" UNF - nothing more - nothing less.
This may seem like a stupid question but do you have an adapter fitter without realising it.
A photo of the head (as is) in the area of the temp gauge take off point would be of help in trying to resolve your problem.

[Bill_qaz]

I fitted one yesterday to 1098 engine (smiths replica) capillary, it came with adaptor bellow but bulb with sleeve nut screwed straight in,without adaptor, it felt a little loose in threads but once pinched against flange on bulb tightened ok with no leaks.

20220223_153706.jpg (1.43 MiB) Viewed 955 times

[CaliTrav]

Forum isn't letting me post photos but since I took an internal adaptor piece out, I'm certain there isn't one there now. When I got the head it had the electrical temp connector attached, plus the adaptor piece for that. I removed both.

As per my measurements, it's coming out at exactly 5/8 in size. But the 5/8 male adaptor piece is about 0.3mm smaller, hence why the threads aren't coming into contact with the head. I can push it in and out by hand, no resistance.

I've ordered a 3/8bsp to 5/8unf fitting. In theory 3/8bsp is about 0.5mm too big to fit the 5/8 hole, but it's the only other widely available adaptor I've seen, apart from 3/8npt which really would be too big, and it might take up the discrepancy in sizing as above.

Is the 5/8 thread an insert rather than cut into the head? I can only assume that's what I removed accidentally, hence the bigger aperture.

Thought I'd measure the I/D of the adaptors on the capillary side - they're averaging at 14.35mm, not including the depth of the threads. The 5/8 capillary nut fits either perfectly. The O/D of their threads are measuring 15.58 as mentioned before - the mm-ish gap between I guess is the thread depth.

However none of these are as large as the existing hole which is 15.88mm - but that's puzzling since that's 0.625" or 5/8 on the nail.

It isn't large enough to be 3/8bsp or 11/16 by my measurement. So is it still 5/8 but needs a helicoil/thread insert?

[Bill_qaz]

Inside of my adapter is about 14.25 not included thread depth so that must of been size of hole in head as gauge bulb screwed straight in, the OD of the adaptor supplied but not needed is 21mm to outer of threads way too big..
Do you think someone has put a threadsert in after damaging it, the solid type not a helicoil which is what you have removed?

[philthehill]

The head is 5/8" UNF with no insert - the adapter is what enables the different capillary tube bulbs to be fitted.
Below is a photo (just taken) of a 'A' Series head with a 5/8" UNF tap screwed into the temp gauge take off threaded hole.

head tap 1..JPG (2.03 MiB) Viewed 940 times

Below is a photo (just taken) of the male/male adapter fitted to my 'A' Series cylinder head to allow the capillary tube bulb to be fitted.

head tap 2..JPG (1008.12 KiB) Viewed 939 times

[CaliTrav]

Then I can only conclude this one has been drilled out in the past for reasons unknown.

The two 5/8 adaptors I have fit each other but not the head. Will see if the 3/8 BSP is better tomorrow.

[Bill_qaz]

Same as mine Phil except my capillary had a male thread that went straight into the head without an adaptor. Calitrav could you put a thread guage in the drilling to get the tpi as you already know the diameter to get an appropriate adaptor..
Something like https://www.ebay.co.uk/itm/BSW-Whitwort ... 635-2958-0