Refurbishing the plastic and durables heaters

By Peter Laidler

Some years ago I wrote about the plastic heaters fitted to our may ’69 or so Mini’s in replacement of the well known but rusty and rattly but reliable metal cased ones.

According to my 1913 edition of Bradshaws……. Ooops, sorry, wrong subject*. According to my Oct 69 on parts list, AKM 0031 and strangely dated August 1976!!!, page N6, there were 4 versions of these little monsters;

24A-341 24A-3419

24A-3420 CZH-2873

Standard fitment
For Canada, Denmark, Iceland Norway, Finland, Sweden and Switzerland. That should give us a clue…..

Given as ‘except mini van and pick-up’ and last but not least;

Given as Canada only. (* usual start of a UK railway TV programme)

From that it would appear that 3419 and 2873 were for extreme cold conditions while 3418 and 2873 were the home or temperate market heaters given that most parts are interchangeable.

But why the plastic casings? As told to me by one of the Tech Managers at Smiths at Witney…… The plastic rounded ‘crushable’ safety-related heater came about as a safety related product for certain European Countries. It was designed to be interchangeable between several of the BMC/BL small car range. Nope, I don’t know of another that uses it either! But that was the reason why the rear bolt location could be adaptable as we’ve discussed on the forum several times. A bit more left or right built in to the 1.75” long mounting bolts extending out from each side and therefore easily adaptable.

So far, so good. It was made for left hand drive cars……, that is, the heater hoses came in from the RIGHT/passenger side into the radiator in/outlet pipes that protrude from that side of the unit. So it was used for the LHD cars. With me so far?

While not exactly a silk purse, it’s not the sows ear that it once was. Perfect working order and easily acceptable for a lightly restored or needy car

It transpired that being a thermo plastic two part(?) pressing, Smiths found that this heater was actually cheaper to make than the standard steel pressing and screwed together standard heater unit – and profitable too! At that, BL decided to fit them to all of the cars, even the RHD spec cars but they had to use the stockpile of metal heaters up. I don’t know the change-over date but I know my April 69 cop car had metal and new Dec ’69 S had plastic. From the discussions here, we can assume that it was what we used to call ‘a phased intro’. But there’s more. Clearly some of these heaters were manufactured from a material known as DURAPLAS – or Durable Plastic….., as in Trabant cars. You can actually see the small cotton fibres within the resin type casing – just like the Trabant cars. We also used a sort-of similar material in the 50;s called ‘PAXOLIN’ . The quality control of the Smiths DURAPLAS casings are what can only be described as, er……., Well, maybe Smiths should have gone to Trabant and learned a few lessons about quality control.

All was not well with the plastic heater unit in the RHD cars. They were like Mickey Mouse wrist-watches. They LOOKED good but they weren’t much good for telling the time – or keeping you warm. That was because, being made specifically for the LHD cars, it meant that the in/out hoses now had to take a looooong convoluted path INTO and OUT of the car through the left bulkhead, down, into the car and then take a sharp right turn, across the top of the heater unit……….. Stay awake at the back of the class….. where the problem gets worse. The two hoses then had to do a sharp 180 degree turn back on themselves to mate up with the heater unit inlet and outlet pipes. In short, the slightest kink and the heater just wouldn’t….., er….., heat! BL soon became plagued with warranty claims for duff heaters.

And that was the cause of most UK mini owners having to pull off, into dark laybys or off the beaten tracks just so that the drivers could induce – or inject – a bit of warmth into their freezing female passenger. Call it the price of being a caring lad. Well it certainly was in my part of Wiltshire and Berkshire which I blame on my dodgy heater. But I digress.

Failure to heat wasn’t the only problem. The plastic (as opposed to this Duraplas) cased OFF – SCREEN – CAR flap part was retained by two small leaf springs engaging into the plastic casing……… But not for long. Set the flap to OFF and open a side window and the flap would simply flip open to CAR, blowing hot air into the car unless you……. Anyway!.

The dealers were told that all they needed to do was to re-position the hoses. I mean….., where were they supposed to stick them (answers on a post card please)? It was across the top of the heater where they were or on the floor, under the bloody heater. It was no good changing the heater because the next one, the replacement, was the same! You couldn’t make it up

The real answer was to….. wait for it…. To remove the heater, strip it down totally and reverse the matrix. But, alas, the plastic heater was made for left hand drive cars and originally didn’t have openings in the casings for right

hand cars. BL were sat on a whole lot of LHD heaters and casings earmarked for RHD 1969 car production. Smiths of course had supplied exactly what BL had demanded and ordered!

Plan view of the partially rebuilt heater unit. Note the heater matrix outlet and inlet now facing the LEFT side of the heater hoses. No more restricted flow now…….

That’s the end of the elongated history lesson so I’ll get on with showing how we refurbished one of the Duraplas versions that had been through the wars. Not only that, how we converted the radiator part to make it more efficient.. Smiths told BL that they (Smiths) could modify them – at a price. In the meantime, the steel heaters went back into the cars for a period while the plastic ones were returned and modified at a sub assembly plant (at Leamington ?). While this paper deals with the impregnated Duraplas casing, by arrangement, we’ll be dealing with the similar-but-different late Mk2 plastic heaters over the winter.

As removed from a needy car. To be honest, this example was at the point of being scrapped. But needs must as they say. Notice the intake and exit pipes on the RIGHT hand side. Not a good idea for a R/H drive car! Note also the fleck type material embedded within the resin type plastic. The only GOOD part is that this material repairs well with superglue.

OUR DURAPLAS HEATER.

What a sorry sight our heater was. Thanks to Nick Rogers, Andy the engineer and James the chemist who’s expertise we used to flush 20 years of crud from the matrix. Before we start, can I suggest that if you’re contemplating doing the same to your heater, forget the cheap stick-on foam and buy yourself a cheapo 2mm thick high density foam camping ‘roll-mat’ for a couple of quid. As shown in the photo as you’re going to need some soon, Stuck on with Gorilla glue, it’s better than anything else. And something else too. Make sure that if you are rebuilding a DURAPLAS heater casing, that you have a tube of GOOD QUALITY, super-glue handy. I used LOCTITE. Due to the very nature of duraplas, superglue works wonders on cracks

Right, let’s start. Stripping is fairly simple and the photographs show how we worked our way through it. Before that, check the wiring, switch and that the motor works. You’ll see that as per most heaters, the foam seals had flaked away and bits were everywhere. In order to simplify the next stage, can I suggest that before you take the flap part away from the lever part you take a couple of photos of how it all goes together.

We carefully removed the thin alloy fascia front plate using heat and chemicals. Then paint stripped the actual fascia bracket and flap and repainted them. As you saw, one of the mounting screws had pulled through the casing. That was made good by using foamboard material cut to shape and reinforced internally and externally, sandwiched by steel washers secured in place by gorilla glue. Best shown pictorially. Then came the length of threaded rod or tie bar.

As for converting the heater to left-hand-feed, that is a simple matter after thoroughly flushing the matrix through in neat bleach overnight. I put a ring

of white crayon around the outer edges of the IN and OUT pipe ends, slid the matrix into the left side of the casing where the crayon marked the casing and bored the new holes to suit. Hoses now directly IN and OUT!

Assembly after thorough cleaning was pretty much a reversal of the stripping. So I’ll let the photos and captions tell their own story

From the top and below. What a sorry state. Even the fascia plate and label had come adrift. Luckily, when the plate had been straightened, slightly blasted and painted, the alloy label part was easily glued in place using GORILLA glue but be careful to read the label regarding wetting the surfaces

Taking the casing apart by flicking off the spring clamps. Hook the screwdriver blade in twist and off they come.

 

Don’t do this in the house!! Stripped into two halves you can unscrew the motor screws, and the……. Look, it’s pretty straightforward whatever you do. The main flap part, just visible has a foam-lined edge that faces the FRONT. More about that later

This has always been a problem with the duraplas cases. The poor mechanical design of the mounting screws. However, the structure of the duraplas material does lend itself to repair by superglue. On ours as you’ll see

  

later, we plugged the hole, reinforced it internally and externally and………

……and used a length of 1⁄4” threaded rod or the metric equivalent, right through the rear of the casing. It is well clear of the motor and fans. While the load on the rod is the same, the shear loading is virtually nil. If you don’t do anything else, do this!! Also shown the cut-off screw and a suitable replacement, But not as good as the new full length threaded rod.

James the Chemist came into his own here. The heater matrix was packed with dried crud! After being filled with neat bleach and left overnight, the matrix was fixed to the mains supply and flushed clear.. On a second overnight we did the same, a bit more rust crap followed and that fixed it perfectly

We reversed the RIGHT side heater hose holes to the LEFT side (see 14).
Don’t worry….., the black high density foam on the rear of the cleaned out matrix petty-well blocked the holes. Note also the block of foamalite plastic we used to repair the hole torn out by the mounting bolt. The foamalite bonded superbly with the Duraplas.. We reinforced the parts internally and externally with steel washers bonded on.

Instead of faffing around with rubbish cheap strips of insulating foam, we bought a simple roll-mat used for camping (Blacks or Millets). It’s 6” long and cheap and has 1,000 other uses around the car and home too.