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MG MGB Technical - Toms Knob/ Drain Tube

In cleaning years of crud out of it, I have managed to detach the drain tube from the air box spigot, which is partially broken and quite rusty. I think there is enough spigot left to attach some hose to or even get the original back on.

I need to get at it though - having had a poke around and looking at the Gaydon cutaway I need to remove the screen air vent pipes from behind the console, and the plastic tubes that run forwards to the heater box.


Before I pull the air vent tube tube out, it there anything I need too be aware of? I take it is just a push fit to replace it. I do not want to create more problems!

Also, if when it comes to it there is not enough spigot left, any suggestions for attaching a tube or a workaround to get the water out of the upper chamber, and through lower?
Mike Dixon

It's been decades since I had a MGB so I might be wrong - I think I remember a blanking grommet, possibly whiteish semi-translucent, in the footwell area(?) that allows side access to where you can get at the clip holding the hose to metal tube, but I might be imagining this all - or I might be thinking of access to a control cable.

As you can tell it's best to wait for info from those that know what they're talking about as I assume you've already looked on Paul's site for info, if not look there.

As a general bit of info these types of jobs, or any on the car, you don't want to impose too much of a time limit on yourself. For me it's always the quick jobs that I think I'll do after completing other work that end up causing extra work as I should have left them for for when there was more time, and light and better weather, and for when I was better prepared to do that work, like time to get the correct fittings or parts or replenish consumables.

Never worry about how quick others can do any work (or say they can) take your time. My time is hours spread over a day, ot two, for a small job and at least three days (possibly over weeks) for a big job. If I complete sooner then great if I don't so what. Sometimes doing a job slowly and in stages can work out being quicker, leaving things to soak, soften or gravity drain whilst you go away for a mug of tea, or a lot longer, can help. Speeding some processes up can really slow things down, despite what I put before, I know from experience.

Also probably best you don't apply for a job at a massage parlour.
Nigel Atkins

Wow, whatever next I remember correctly about the grommet.

Found this in Archives, it's from Paul so probably also on his site, perhaps with lots more info.

I'll keep looking in Archives.


Nigel Atkins

https://www.mgownersclub.co.uk/forum/mgb-technical/replacement-heater-drain-hose-toms-knob

Mike, some info here.
Craig M Harvey

And I've finally found where info is on Paul's site - http://www.mgb-stuff.org.uk/heatertext.htm#airb
Nigel Atkins

Certainly easier to get at clip on earlier cars as per Dave's and Paul's photo below.

If the metal spigot is shorter a narrow band clip or fixing might be needed.

I've seen the bottom of hose described as a dust valve, I always thought of it as a dump valve but more for weight of water and perhaps debris but of course as the rubber ages it becomes less flexible so less of a dump valve. This causes the collection and build up of debris as the lower volume of water flow washes the dust down the hose but not so well out of the now rigid slit valve opening.

On a car with unknown history to me I'd start the crud evacuation process from under the car. Warm rubber slightly with a hairdryer first to get a little more flexibility to it then gently scrape out crud from slit opening on the end bowl.

When I got a clearing of sorts there I'd then use something like a straighten wire coat hanger to gently clear a hole through the length of the drain hose and it's crud.

With funnel and hotish/warm water prepared I'd again go under the car to warm the rubber with the hair dryer, then quickly back up top to pour hotish warm water, gently rod through from top and then back under car to gently clear valve bowl as much as possible. Repeat whatever parts of the process required until warmish clear is all that runs out the bottom.

Very often a bit more time and effort put in at the start can save a lot more time, hassle and expense later.


Nigel Atkins

Thanks. I cannot get into the MGOC site as I am only an MGCC member

I had seen Paul's stuff and have got that access grommet. As the tube has fallen off I need to extract some of it ( having cut off the bottom) , probably complete with jubilee clip as I cannot hold in place and get a screwdriver on it

I also found a thread on this site about 'Toms Knob dropping ' from 2012 in which Paul recommended the route I am taking via the heater tube aperture - hence my question about tube removal/replacement

I think I will have to use the heater tube route anyway to get a new tube back on given the state of the spigot - looks to me like you can get your hand in there, just , rather than just the end of a screwdriver which is all the access hole really allows?



Mike Dixon

Mike,
you done your research ahead of me then so apologies for repeating.

In case you didn't see one post on this subject, be very careful of sharp or jagged edges, minor wounds can turn very nasty sometimes.

Do you mean the drain hose has fallen off or (part of?) the metal hanging spigot?

And you cut bottom of what?

I'm thinking of Aussie John's idea on Paul's site.

(Update on your profile would help with which year your B is.)
Nigel Atkins

Thanks - I think John's route is the one I will go. I will cut a hole and cover it with a plate or firewall bung thing.

I have tried getting in via the heater tube route , albeit without removing the tubes completely, but I cannot get my hand to turn back sharply enough to get more than a finger tip on it which is not a lot of help.

As folk have noted it's one of those jobs that needs doing but you would rather not have to do. Should have got some shares in Elastoplast as well.
Mike Dixon

ETA: I can't get int MGOC forum either.

Always good 'fun' messing around in the footwell, at least there's more room than in the Midget.

I think I looked at mine with the heater out when refurbing and upgrading the heater but I can't remember now and can't remember having problems attaching the heater control cables but it was a long time ago and I didn't loath working on the car then as the BGT was my introduction to stupidly overpriced old British cars called classics, before this they were just old British cars, which were always best avoided.

The heater and its seals replacements seemed a good improvement in spring but in winter all the B and GT draughts reduced the gain greatly. Nowhere near as cosy as a Spridget cabin the B heaters can be improved by internal and external cleaning and replacing of internal and external seals, setting of cable heater valve end and I wondered about better sealing to the fresh air flap.
Nigel Atkins

The maim purpose of the original rubber tube is to allow water to drain out of the air-box without fumes getting up there into the cabin, although air-pressure in the air-box should prevent that anyway - when driving along at least. My V8 has had just a plain tube since I bought it 25 years and 120k ago and not caused any problems.

As long as the hose projects below the tunnel it should be OK. If pulling it around fractures the spigot then water will run into the area between the bottom of the air-box and the top of the tunnel and probably into the car from there, and even if not will lie there. Take care!
paulh4

Thanks - all the more reason for a decent sized access hole, from what I can feel of the spigot I will have to be very careful.

My fallback/disaster recovery plan is something along the lines of a plumbing hose back plate glued in place. Hopefully it will not come to that.





Mike Dixon

Mike,
I think potentially there's all sorts of solutions with funnel, over sleeving, inner sleeving and others but all might be be a royal PITA to do especially if the metal spigot breaks and the higher up it breaks so again it's one of those jobs where you don't want to be in a rush or with too much of a time limit.

Let us know how you get on.
Nigel Atkins

Had the same issue when I had water dripping on my feet. I used a thin flexible plastic hose and gently "rodded out" the drain until the blockage of debris softened to the point of "liquifying". Suddenly there was a rush of water and debris coming out from under the car. Once that cleared,I ran a garden hose into the cowl and let it pour for a while.

Let us know how your issue turns out.

Cheers

Gary
79 MGB
Gary Hansen

Well, it’s going well so far!

Access hole duly cut to get at the spigot and working with a Dremmel from below I have cut though the drain tube allowing me to get the top section out.

Having chipped out the rusted remains of the lower part of the spigot from the tube , the good news is there is enough spigot left for me to re-attach the original pipe. I have discovered a length of heater hose is a perfect interference fit to join the two halves up again – a bit if a fiddle under the car but doable, before reattaching the top.

The slightly bad news is a bit of rust perforation around the drain hole opening. As most of you will know it is set in a slight recess or water trap when the drain hole is blocked, so the perforation is in a nice line!

I have given it some rust treatment and am managing to get some fibreglass reinforced filler applied from below which with luck should last a few more years. I wonder if there might be a better way such as popping a shaped plate on it but I have no idea how, even during a restoration this would not be the easiest job? I will put plenty of waxoyl in both upper and lower boxes and leave it as I have it.

Not quite keyhole surgery but close enough for me and I can see why I been procrastinating on this one. Final assembly needed but so far so good.

Thanks for the help and encouragement
Mike Dixon

Well done.

I've totally gone off of Waxoyl better I think to put on rust converter if required and then build up thin layers of paint if you can.

Where I've had black waxoyl put has then hidden rust that's developed under the waxoyl unseen. For cavities I'm now using dynax S-50, out of cavities the excess drips off but is easy to wipe up.
Nigel Atkins

I've known people remove the heater and cut the front out of the air-box to get access to repair the drain.
paulh4

This thread was discussed between 21/03/2021 and 24/03/2021

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