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MG MGA - Heater valve

As it’s quite around here , I thought I’d ask for a little,simple help from others experiences.
I need to replace the heater valve. I did it about 10 years ago, but I think my arthritis, bad back, etc makes everything more of a challenge these days!
Of course it’s an easy enough job but the bottom bolt is hidden away and so looks so awkward to get to. Especially because of the profile of the heater valve itself, meaning that it looks as if only an open ended spanner will fit. And that needs to be more or less pointed down to the ground, with little room to manoeuvre. I could take the distributor out but that seems a bit daft.
So maybe I need to butcher an old 7/16th or 11mm spanner and shorten the handle?
Thanks
Graham V

I found an old mini socket set I had forgotten I even had, and it did the job perfectly.
But with these cars, one thing always seems to lead to another. As you will see from image 1, I discovered that the vacuum advance pipe was disconnected - the chances are I did that whilst trying to remove the heater valve bolts, but I also discovered (see image 2) that the previous owner must have connected it to the distributor using a piece of hose pipe with a small pipe inside it to fit the vacuum advance!
I see it should have a nut and olive. Does this just slide on to the copper pipe and fix when tightened (like domestic plumbing compression valves), or does it need to be brazed? I hope not, as that will be above of my pay grade. Or maybe I need to buy part 1H919 but thats always tricky to fit on the carb, so I would rather escape that if possible!
Thanks







Graham V

Graham. It has been many years since I worked on a distributor having the solid copper line with fitting, so I do not have an exact answer. But, the following might get this started. First, the fitting is not brazed to the copper line because it needs to be able to screw onto the nipple on the vacuum advance. If it were brazed, the nut could not turn. Second, back in the era of design, the common compression fitting (slip the nut onto the line, then the compression fitting, then attach to the nipple) had not been thought about yet. Thus, the most common method of holding the nut onto the vacuum line was some form of flared end similar to what is used on hard brake lines.

All that being said, the first step would be to hook up a vacuum pump to the vacuum advance, hook up a timing light to the distributor, start the engine, and test that the vacuum advance is functional. Unless it has been replaced within the last 20 years, there is a good chance it is non-functional now. A replacement vacuum advance unit may, or may not, use the original copper line with screw on connecter. Hence, checking to see if the vacuum advance is still working is a good place to start.

Les
Les Bengtson

Hi Graham.
Good idea to see if a 7/16th socket will allow you to loosen the lower bolt. Do you have a clip and bracket for the temperature line from the head as items61-64 in diagram?
I also think my distributor pipe is connected to a threaded advance on the distributor with brass nut?
Regards Brian


Brian Paddon

Les
Thanks for your help. That makes sense. And I have just seen confirmation, as you say, its like a compression fitting on Barney's site at https://mgaguru.com/mgtech/ignition/ig120.htm

Brian
No I dont seem to have a separate temperature control, just how far the valve opens seems to be the only control over that.

Graham V

Hi Graham. I think I have caused you some confusion. The clip I mentioned supports the capillary pipe from the cylinder head giving the water temperature of the engine. The distributor advance connection maybe different as my car still has the 25D unit, in the original 1600 engine.
Hope you are able to sort it out. Just wondered if dissconnecing the hose, removing top bolt will allow you to twist the valve around to enable you access to bottom bolt.
Brian
Brian Paddon

Brian
Thanks. Don’t worry about it.
In the end it was quite easy to take the valve off. I found a tiny socket set I had forgotten I had, but really tiny. The “handle” is just an allen key so very little bulk to get in the way. And the miniature socket is not deep nor does it have a thick perimeter. But it’s reasonably strong and was perfect for the job.
Graham V

This thread was discussed between 17/03/2025 and 18/03/2025

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