Happy new year all.

Does anyone know the correct TPI for the small brass threaded core plugs on a early 1929 coil engine?

I had to remove both in order to clear the badly plugged water gallery they close off. In doing so I destroyed the plugs so will be making new ones.

The thread looks to be 19 TPI but would like confirmation on this if anyone knows for sure.

Thanks,
Stephen

Can you post a picture Stephen?

Here are two pics from different angles:







image hosting over 5mb

I wonder if your block has been modified at some time Stephen. My RP has an early block with screw in core plugs but the gallery next to the manifolds has a knock-in plug whilst the main core plugs have squared centres not slots.
Here's mine. Rear end of block is the same.

Location: Gard, France 30960. Used to be Languedoc-Roussillon but now it's Occitanie

Hi RR,
to my knowledge the block is original and unmodified as the head of the small plug matched that of the large one with the same type of slot in the head.

Of course that doesn't mean to say that it couldn't have been altered in the past sometime.

Stephen

Thanks Stephen - the ones I have experience of are like RRs as well - hence my photo request.

Sorry not to be able to offer any more help.

the large plug can be either slotted or square. both are original austin.

ive only noticed knock in core plugs on the small plug.

but early plugs may be brass.

is there any date or engine number on the block.

thanks tony

Location: huncote on the pig

Tony the block /engine number is M79673 as stamped on the crankcase and lower

edge of the block below the valve chest, but 72719 is stamped on the front

face of the block by the core plugs. You can make out the end numbers in the

photos.

Stephen

Hi Stephen,

My April 1929 Saloon has engine number M 83747 and original block (didn't check the number).

The block main screw in plugs have a slot (as do the other two 28/29 engines).

The gallery core plug was a drive in as seen in the above picture but when we overhauled this (and the other two) we drilled and tapped for brass screw in plugs to enable the gallery to be cleaned.

The plugs are different on each engine and I would say your block was modified at some time in the past to take whatever brass plug was to hand.

I would think you will just have to buy/make a plug to suit your particular conversion.

Cheers, Tony.

Location: Melbourne, Australia.

Hello Stephen, it should be possible to check the TPI of the drilled out plug pieces, which you may have already done to get the quoted 19 TPI which will be a BSP or BSPT thread It should be possible to measure the tapped hole and work out the thread size and get hold of a plug or something with a BSP thread to try in the hole, assuming that you are using the existing threads.
Brian

Location: Near M1 Motorway Jtn 28

3/8" Bsp = 19Tpi
.656 core dia
Roger

Location: Haverfordwest

For info my block with the squared end core plugs is slightly later having a number somewhere in the region of 140000 stamped into the valve chest (I can't remember the exact number). It dates it to some time in 1930 if I'm not mistaken. Perhaps Austin changed over from slotted to squared end plugs round about then?

Not sure that changing the design actually made them any easier to remove once they'd rusted themselves in. The one on the back of my block looks like a practice piece for apprentice (and failed) chisellers...

Location: Gard, France 30960. Used to be Languedoc-Roussillon but now it's Occitanie

Thank you all for your input.

What you have said about the plug being a drive in one originally is what seems to be shown in the majority of the period photos. This had me scratching my head a bit but now it makes sense.

Since it is unlikely I can find a threaded plug off the shelf here in Calgary, I'll just machine a pair from brass stock.

Stephen

I have had need to remove the two brass core plugs on an early block and they are indeed threaded and then peened over on the outside.
Taking Roger's advice on size I milled the peening off flush and drilled to core size for 3/8"bsp. revealing the thread. I then picked out the remains of the brass and re-tapped 3/8"bsp.
I can understand that people think that they were peened in but this is not the case, they were threaded originally.
It is a good idea to remove them because the gallery was completely choked up with crud.
Hope this is of interest.

Location: Deepest darkest Kent