Dec 112013

The heater housing was too far gone as almost all the panels had either rusted through or were paper thinUnfortunately the heater box was beyond economical repair. The entire bottom section was paper thin and had rusted through in places. The side joints hadn’t fared much better and had rusted from within causing the joints to swell.

Every time the heater housing was rotated to inspect it, showers of rust fell from every opening! The motor and fan cage were also missing.

The heater matrix within is surrounded by a thick felt material and I suspect that this had acted as a sponge. The absorbed water had sat against the base and sides causing them to corrode over a prolonged period of time.

The padding material for the inside of the heater are available as a 'complete' kit ... excluding the padding between the heater and the bulkheadFortunately new heater units are available (although not that cheaply), so a new one was ordered along with a heater matrix and a kit containing all the various padding materials.

Oddly the padding kit didn’t include the square rubber seal fitted between the heater body and the bulkhead.

If you were going to the effort of replacing all the internal padding, it’s likely you’d be working on the fan housing off the car and so would probably need to replace the bulkhead seal too!

On the positive side, the new heater has an improved design for the fan cage which hopefully might address the reported problems with the original, asthmatic unit. The blades on the original fan cage were flat and aligned radially which isn’t the most efficient in generating a throughput of air. The new cage has curved blades angled towards the direction of rotation.

The heater motor can be switched between two operating speeds and is achieved by introducing a resistor into the circuit to reduce the voltage across the motor. It’s riveted to the motor’s mounting flange and the loom wires soldered in place rather than using spade connectors. I’d stupidly expected a new unit would come with the resistor attached!

The padding around the heater matrix is a thick fibrous material and it was a really tight squeeze to fit it all in. At least the matrix won’t be able to move around!

I found it was necessary to glue the square foam seal to the heater box with contact adhesive, before fitting the heat to the bulkhead. Otherwise, with only one pair of hands, it tends to fall out of place when attempting the fiddly task of fitting the mounting bolts while supporting the heater unit.

Heater Matrix & padding Bulkhead seal glued in place Heater unit installed

Fortunately the rubber connectors and ducting behind the dash were all present and in good order. So they only needed cleaning in soapy water to remove the grime that have built up over the years.

Sep 162013

The heater valve was another part that was difficult to remove, as the bulkhead heater pipe had seized solid into the valve body. I didn’t want to apply heat in case it damaged any internal rubber seals and so I tried to break the joint by rotating the valve body. All this achieved was to deform the pipe, which eventually had to be cut to remove the valve.

There were signs of weeping from the valve so I suspected an internal seal had started to deteriorate and it would need replacing. The valve consists of a pot metal valve body and a plated end cap. The body has protrusions around its circumference which interlock with corresponding hook shaped protrusions on the end cap and then a single rivet stops the end cap rotating relative to the valve body.

The rivet was drilled out and then it was fairly easy to split the valve in two by rotating the end cap. This revealed the cause of the weeping – a sprung rubber diaphragm, that is used to control the passage of water, had become furred up.

The deposits had compressed the rubber seal in several places so it no longer made a complete seal. The rubber had also hardened over time so wouldn’t spring back fully once the deposits had been removed.

Even after extensive internet searches, I haven’t been able to find a supplier that just supplies the internal rubber diaphragm. Unfortunately the options are very limited.

Either purchase a complete repro valve or a repair kit from an American site, which includes everything but the valve body. However the kit was considerably more expensive than the repro valve, so I went for the latter.

Overall the quality of the new valve was fine, only let down by the finish of the valve body casting. It wouldn’t make any difference to the operation of the valve but I would have preferred to keep the original body.

Feb 142013

The dash heater controls operate plastic vent outlets on the underside of the dash, one in each footwell. When the vent is open, the air follows the passage of least resistance into the footwells. By closing the vent, this path is blocked and therefore the air is forced to exit via the dashtop windscreen vents.

The vents themselves consist of five interconnected vanes with the central vane connected to the dash control. Operating the dash heater control rotates the central vane, and with it the other vanes, between the fully open and fully closed positions.

Somehow the central vane of one of the vents has either been misplaced or lost during the constant sifting through the boxes of parts. Unfortunately the vents seem to be unique to the Series 2 and, as far as I’m aware, are not available any more.

After fruitless searches of the parts boxes and keeping an eye out at Stoneleigh spares day, I had to bite the bullet and start researching if and how I could fabricate a new vane. The problem is that without the central vane the vent is useless.

I think most plastic parts are generally injection moulded which isn’t really a DIY option. However there are some very low viscosity polyurethanes available that are suitable for moulding which may produce a good replacement. At least having two vents meant I still had a central vane to make a mould from!

A order was placed with MB Fibreglass Supplies who were very helpful in explaining the moulding process and several days later some RTV Silicone Mould Making Rubber (Polycraft GP-3481), Fast Cast Polyurethane Liquid Plastic Casting Resin (Polycraft FC-6720) and black polyurethane pigment arrived. Some white modelling clay (water clay) was also required, which can be obtained from most craft suppliers.

The first step was to produce a two piece silicone mould of the vane. Four ‘L’ shaped pieces of plywood were fabricated with a depth of around 3″ to make a mould housing. Using ‘L’ shaped pieces has several benefits; they can easily be moved relative to each other to obtain the desired mould footprint, clamping together is straightforward and they can easily be removed at the end without damaging the mould.

The mould housing is then half filled with the modelling clay and clay rubbed along the each of the corner joints to seal them. An off-cut of wood and some coach bolts was used as a mini tamping device. The vane was then pressed into the clay until the long lengths of the vane were flush with the clay (ie half above and half below the clay). Finally a number of indentations were made in the clay which will act as key for both sides of the mould.

It was now time to make the first half of the mould with the two-part silicone system, mixed by weight – 10 parts rubber to 1 part catalyst, ably assisted (hindered) by my two nieces who were on mixing and pouring duties. Being a red colour, it was easy to see when the catalyst had been fully mixed into the white rubber part. The mixture was then slowly poured into the mould housing, covering the clay and vane. The technique is to pour slowly and in the same place so that the silicone pushes out the air as it flows over the part being moulded.

The Room Temperature Vulcanizing (RTV) silicone normally cures in around 4 hours although I left it overnight as a precaution as it still felt tacky after 4 hours, probably due to the cold weather. The mould housing can then be turned over so the clay can be removed, to reveal the first half of the silicone mould with the clay indentations now appearing as small peaks.

Traces of residual clay were removed by wiping with a damped cloth to prepare for the making of the second half of the mould. Once dry, the first half of the mould was lightly brushed with Vaseline, diluted in white spirit.

This should act as a releasing agent stopping the second half of the mould sticking to the first. Some more two-part silicone was then poured into the mould housing as before and again left overnight to cure. Now for the moment of truth …. will two halves separate?

They actually separated very easily and the original vane came out without damaging the mould. The quality looked very good although the proof will only come once the new vane had been cast. The final preparation of the mould was to cut a conical channel for pouring in the polyurethane casting resin and an air vent to help prevent trapped air bubbles in the cast.

The polyurethane resin used was a two part product which naturally cures to an ivory white colour so a small amount of black pigment is required to get the desired finish. The mixture ratio by weight of resin part A, part B and pigment was 10:10:1 so the main difficulty was weighing the three parts accurately as the part only weighs 4 grams.

The resin cures in approximately 60 minutes so it wasn’t long before the first cast was ready. The initial impression was very good – even the original casting marks were faithfully reproduced. However the part was far too flexible so the nieces rudely declared it a ‘FAIL’.

MB Fibreglass Supplies were again helpful and thought the cure process had probably been compromised, most likely caused by having insufficient temperature in the component liquids when they were mixed.

A second casting was made after first heating the liquids on a radiator. This produced a much stiffer vane which seemed to stiffen even further once it had been removed from the mould and left on the radiator overnight. I now had two operational heater vents!!