OK - time to fall back on the collective brain again.

I headed out this afternoon thinking that all I needed to do was drill access to the hidden ducting screw, move the ducting to one side, and access the matrix pipe clamp.... Eh, no. Maybe it's that I'm pussyfooting around and haven't gone all RRAAWWR! and medieval on the plastic parts, but I'm just not seeing how, even having followed the instructions, I can get good enough access to the matrix/pipes.

The pictures in the 'wayback' instructions don't include any looking down into the empty dash area, so I've marked up a couple here.

In the pic above you can just see the temperature sensor clip on one of the heater pipes. But immediately after I took this pic, I did manage to move the air duct a little further - down and back (at the bottom end) - but this brought it hard up against the plastic cable duct (which the instructions have not mentioned moving. Now that little gap has closed:

At the moment, unless I can get the duct to move considerably more out of the way, I don't see how I'll be able to do this job without taking the dash out. The plastic panel, that was drilled to access the ducting screw, needs to come out at least. I'd already loosened it to allow me to get the ducting this far.

I can, just get my hand in to the matrix at the moment, with my wrist flexed backwards, but there's no way I'd be able to get two hands in there, or have enough room to clean pipes or install O rings and manouvre pipes and clamp back into place.

I guess the only question I have is about the ducting. At the moment, if I pull it away from the heater at the top, it just slots right back into place. If that needs to "off", and I also need a hand or two to manouvre the lower end of it, then I'm going to need someone else to help. I don't see how I can access both ends of this duct at the same time, with sufficient grip/strength to move it. And finally, where am I putting it? The 'wayback' instructions say it can be 'swung away'... and at the moment, I'm not seeing how I can get to 'swing' it anywhere, far less out of the way.

Those instructions also mentioned that someone had removed the dash top to do this job, and thought it worthwhile. I must admit that's where my thoughts are at the moment.

(Edit - been doing some more searching too, and the other option is of course to get the multi-tool onto the duct. I saw one reference to a 'preferred' place to cut it - but the pic was missing. I don't "like" cutting things like that, even if it doesn't make an awful lot of material difference, it seems like a 'bodge' to me. But if needs must....)

There's a familiar view, I spent most of the weekend looking at that very same thing. A few months ago I replaced the heater matrix on Nigelbb's car but his carpet still seemed to be wet so he dropped it off so I could have another look and see if I'd cocked up somewhere. I ended up taking the whole lot out so I could have a good look and then pressurised the cooling system up to 20 psi so I could watch for any coolant coming out. Pressurising it showed that the reservoir pressure cap was leaking but nothing coming out of the O rings or matrix so it all went back together again. On that, someone had been in there before and had cut the duct as high up as it can be seen looking through the hole so only the lower part has to be pulled out. Even then, due to the shape of it, it still needs a good tug to get it out although it slots straight back in when you come to put it together. Having found no signs of a coolant leak and the leaking cap would explain why he was losing coolant, took the trims off so I could lift the carpet and found it sodden with water but clear water not coolant. Seems his plenum was leaking rainwater in adding to the coolant that was already there.

Taking the instrument panel out will let you see things a bit better but doesn't help with removing anything so while some will not approve and it does seem like a bodge, I'd say cut the duct up around the blend motor level. Just be careful that you don't nick the alloy pipes behind it or you'll have an even bigger coolant leak. When it goes back together you can use duct tape for its designed purpose to join it back together and seal where you cut it. I can see where you've drilled the hole to get at the hidden screw but to get on the screw absolutely perpendicular you'll need to put the hole in the side panel to the left and slightly higher of the hole you've already got. The wayback link shows where someone put two overlapping round holes but I normally use a cutting disc on an angle grinder to put a diamond shaped hole there.

When you put the O rings back, get them in place then start to do the screw up. Once it starts to do something, give the pipes a wiggle to make sure they are fully home before tightening it fully. Once you have changed the O rings, start the car up and let it run up to temperature so you can confirm it isn't leaking before putting everything else back in.

Firstly I would enlarge the hole you have drilled to access the heater duct upper screw in a horizontal direction towards the rear. By viewing through the enlarged hole and behind the moved ducting you should be able to see the infamous screw head and the long pozidrive No2 screwdriver can be inserted to engage. Unclip the temperature sensor off the pipe (the wiring prevents the pipes being moved towards the engine compartment). There are now two options:

1. By feel undo the screw and then move the released collar back along the pipes and then push the pipes towards the engine compartment. Then, mainly by feel, the o-rings can be removed, the pipes and matrix cleaned up, o-rings inserted over the pipes, the pipes inserted back into the matrix and the screw re-engaged. To facilitate this do not remove the screw from the matrix, rather as you unscrew it pull the collar away from the matrix. Do not forget to re-clip the temperature sensor onto the pipe. If you have big mits like mine this is all a big ask but I managed it the first time I did the o-rings.

2. Through the instrument binnacle opening cut through the heater duct as low and as square as possible and be very, very careful not to cut the heater pipes. Then pull the lower section out from below or move it right out of the way. The upper section can also be removed through the binnacle opening as well once it is cut. With the ducting out of the way the access to the screw, matrix and collar is vastly improved and you can actually see what you are doing. The ducting needs to be duct taped back together on re-installation.

There is a third option to remove the dash which is what I did a few weeks ago but I also needed to re-attach the dash to windscreen trim/seal which had come adrift and also fully lubricate the blend and distribution flaps which had started making ominous sounds as they moved. Removing/replacing the dash is straightforward and not that difficult - it just takes a fair amount of time.

Thank you both. Didn’t mean to give you unpleasant flashbacks Gd!

With two recommendations for cutting the duct, that’s where I’ll be going then.

It’s interesting that there are two ‘inaccessible’ screws on this job, and one hole seems to do both. I now understand why the larger holes have been made. They had seemed like overkill to me, and a bit cack-handed.

I should have a longer go at it tomorrow.

Well, I got there….. and my O rings didn’t arrive!

To be honest, because of health reasons I’ve not been up to scratch since the new year, and without going into any detail, the main impact is a lack of proper sleep. So it’s better for me to do short bursts, rather than long days. So I was happy enough to leave it at lunchtime with just the coolant to drain, and the matrix screw to tackle. I did give it a good going over with Plusgas, so here’s hoping that will do its stuff overnight.

I can see that getting duct tape around the duct is going to be entertaining….

Thanks for the morale support so far.

No need to drain the coolant. It'll start to dribble out when you slacken off the screw but a Tupperware container stolen from the kitchen is big enough to catch the contents of the matrix.

Well, further progress…. But my O rings didn’t arrive!

Managed to track down the last 300mm pozi2 screwdriver in town, so thought I might as well give it a go now that the plusgas has been doing its thing. It certainly was trying to cam out (even with a smear of cutting paste) so a two handed job to keep enough pressure on the end of the screwdriver, and to turn it. A bit of to and fro did help to keep it coming. Quite a bit of thread lock on that from the factory isn’t there? In fact it strikes me as odd that they would put to much thread lock on a fixing with a screwdriver head? Not that I plan to do this again in a hurry, but I’m going to see if I can’t find a hex or torx screw in time.

Even with the pipes disconnected in the engine bay, and pulled back a bit, it’s still awkward to get in there isn’t it - (rhetorical question!). I got the old O rings out - squared off and brittle as expected. So all that needs done now (once the new O rings arrive) is to clean up the end of the pipes, and see if I can’t get some pics of the matrix pipe ‘receiver’ to see if there’s any dried coolant or gunk in there that I should try and get out - though I’m not sure how that would go.

All in all, and coming from someone who started mechanicing on the old BL minis, this job has a high PITA rating for a newbie.

There shouldn't have been any threadlock on the screw, normally, once you get it moving, it unscrews easily but at least it is out. It's an M5 thread so your local B&Q will supply a suitable hex head screw (assuming your local B&Q isn't hundreds of miles away that is). It is awkward, especially if you have big hands, but can be done. Hence my comment that is isn't difficult, just fiddly.

I've worked on Minis (and most other things over the years) and always wondered if Alex Issigonis ever did find out who his parents were. The same goes for the bloke that designed the VW Beetle......

Rejoice, you’ve done the difficult bit! You should now be able to get a finger into the matrix side of the joint and any crud will be immediately felt. Easily cleaned out with a bit of descaling fluid. Further tips:

1. Take time to make sure the pipes are pushed into and fully located into the matrix before doing the screw up and drawing the collar up tight.

2. Do not overtighten the screw especially if you have a replacement hex head screw. The amount of torque you can apply with Mk1 hand and a screwdriver will be sufficient otherwise you may crack the plastic matrix. You can always nip it up a bit if it weeps but once the matrix is cracked it’s a whole heap of further work.

3. Once the joint is assembled refill the cooling system and test the joint by running the engine and coolant up to temperature and pressure. Do NOT turn on the ignition/start the engine without the instrument cluster connected with both connectors - a whole new world of pain awaits otherwise.

4. Don’t forget to clip the temperature sensor back onto the pipe.

5. Clean up the inevitable hairy edges of the cut heater air duct and assemble in situ. To help with the duct tape issue the method I use is to cut a length of duct tape and then ‘stick’ a strip of grease proof paper twice as long as the cut length of tape to the sticky side of the tape and fold it back on itself. The duct tape can now be easily fed through the narrow gap twixt duct and heater box, positioned and then by slowly pulling the grease proof paper off the duct tape can be slowly and accurately stuck across and around the joint in a controlled manner.

Good luck.

PS : Classic Minis - pretty much rebuilt more than one of these. Once I’d mastered the ‘secret’ of the heater by-pass hose replacement I could do one in under ten minutes! There was also an acquired technique for bolting those pesky master cylinders in place. All other jobs seemed pretty straightforward to me.