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Le Tonkinois varnish

Flexidisc sander


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The heating air impeller levered off using two screwdrivers.

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View of the splines on the motor shaft.

Shaft and bearing. The four motor case tabs which had to be bent outwards later.

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The combustion air impeller is easily damaged and using only one screwdriver often breaks the central boss of the impeller. The impeller has to be kept reasonably straight during removal to avoid damage.

My simple low tech solution used two sturdy kitchen knives. Other methods like using two screwdrivers can also be suitable.

These knife blades were 1.5 mm thick and the gap was only 0.3 mm so the knives had to be carefully worked in. After some levering I finally got them passing right through. I could have levered off the impeller using both knives but here I gently knocked in the handles of both knives and the tapering at the handles forced the impeller up the shaft.

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Three T20 torx screws held the motor.

The second motor  screws were different, requiring a hex key to remove.

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Motor ready for repair.

The motor magnets pulled back as the rotor was extracted. The crinkled washer usually remains inside the case stuck onto the magnets.

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Plenty of carbon debris inside the motor 1 created by brushes wearing away. The dust is messy, dirty black hands! There was very little dust inside motor 2.

Magnets and their retaining clips inside the case. No need to take these apart.

Four clips that locate into holes in the side of the black cap have to be pressed in before it can be removed. These clips try to move back into position which makes separation more difficult.

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First part of disassembly completed on motor 1. The brushes were quite worn. The bearings seemed ok but I replaced them at the same time to find out how to do it.

Airtronic models have a magnet mounted in the impeller for checking the motor rotation speed.

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The black cross moulding removed quite easily.

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Cap removed. Two results are possible, bearing remains on the shaft as shown here or bearing remains in cap.

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When Carl Dalmas disassembled his D4  the bearing must have been looser on the shaft and remained in the cap, a better result than both of my D2 motors.

The cup shaped retaining washer covers the bearing. One is also fitted on the D2 but on motor 2 the washer was the other way round.

If the bearing has to be replaced drive it from the other side, that also forces the washer free.

Eberspacher Blower Motor Unit repairs


Air heater blowers have impellers (fans) mounted on both ends of the motor shaft. The larger black or orange impeller draws in the air to be heated and pumps it over the heat exchanger. The smaller brown impeller draws in air from the combustion air inlet port and pumps it to the burner. Water heater blowers just have a single combustion air impeller. We would rate motor repairs on modern Eberspacher heaters as medium difficulty, not suitable for people without reasonable mechanical expertise. If you decide not to repair the blower please donate it to us for experiments and the autopsy pages.

Bearings are more difficult than brush replacement. Parts can be easily damaged if care is not taken while disassembling and we advise only taking apart blowers that have failed. Please feedback comments on repairs and repair methods, good or bad, we learn a lot from users problems and experience.


There are 4 main causes of motor failure, listed with the most common first.

1) Carbon brushes wear until they no longer make reliable contact with the commutator. Typical symptoms speed variations, open circuit and intermittent faults, sometimes a smell of ozone due to sparking.

2) Bearing failure. Roughness can often be felt while rotating the shaft by hand and the shaft may have excessive play. Typical symptoms noise, vibration, speed variations, seized motor.

3) Rotor failure. The windings on the shaft are arranged in several segments that are switched by the commutator and brushes.  If a segment fails the motor can fail to turn but might do so if the shaft is moved away from that starting position.

4) Commutator damage. Some wear of the commutator is to be expected, very occasionally it could be excessive. Symptoms same as 1 or 3 but far less common.





Airtronic D2  D4  blower motor repair

Eberspacher D2 and D4 blower units. Impellers are fitted on each end of the motor.


Dereks D2 failed several times with fault code 33 Blower speed. Other causes like something touching the impeller were checked. There was no obvious roughness or excessive play when the shaft was rotated by hand so suspicions of a brushes problem. Eberspacher do not sell individual parts. I marked the impellers and shaft angular position before starting so they can be refitted to keep the best balance. That may not be necessary and it may still not balance after repair but we prefer to do it. I marked the position on the end of the shaft by filing a very small notch on the edge. I also recorded how far the shaft protrudes or is recessed for refitting in the same position.

This is our first repair of an Airtronic motor and changes will be made when we do the next.  I am an electronics engineer not a mechanic so my mechanical methods may be a little non conventional.

Other methods may be as good or better but it worked for me and is a very good starting point. I did try a lot of experiential alternative methods during the repair especially with the brushes.

Update July 2018. Thanks to Jon Kutassy for donating another D2 blower with open circuit symptoms. It already had both impellers removed but had not been opened, allowing me to try alternatives.

Design changes during the manufacturing life of a heater model are not uncommon. The bearing retaining cup on motor 2 was different. I advise checking all measurements and to photograph while taking apart.

The photos are a mixture of repairs to both motors, click on them for larger images.

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Page 2 continues with replacing the brushes and bearings

The 4 retaining tabs on the case, shown earlier, had to be bent out. This was not easy, the tabs are fairly soft metal but quite thick and fit in a deep recess. For motor  2 I experimented using a centre punch but this was not very successful. It managed to bend 2 of the 4 tabs partially out but the other 2 it just flattened. The strong screwdrivers I had were too wide for the recess slot, the narrower ones were not strong enough. My practical solution was to grind a couple of very old punches that I never use. One punch converted into a very strong levering tool and the other to a strong screwdriver / chisel that could be hammered. Both of these worked well. For a future disassembly I will see if either tool will do the complete task for untouched tabs.

New punches are £1.99 for set of 3 post free on ebay 2018.

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My modified pin punch tool. Probably needs to be ground more pointed for tabs that had not already been bent.

Levering out the tab was easy with this tool. Chisel tool worked better on the burred tabs.

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Screwdriver / chisel tool. Width ground to fit recess. It can be hammered and square end can be gripped for twisting.

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Tabs right and bottom nearly clear,

Motor 2 tabs top and left burred by original center punch causing problems.

On the first motor I omitted to measure the position of the bearings on the shaft, I made sure I did that with the second before removing the cap. At the cap end of the shaft it was 18.6mm from the bearing to the end of the shaft, 16.6mm from the black plastic to the end of the shaft. The other end of the shaft measured 21.2mm from its bearing to the shaft end. Always check in case manufacturing changes have been made.

I have tried 2 methods of removing the black cap. The first motor I pressed in the catches before tapping the end of shaft with a hammer. This took several attempts, the catches often re-latched but the cap did finally come free. A potential problem here is the rotor assembly can be jarred from its position along the shaft as Thomas Nilsson found out with his D4 motor. The assembly can be glued back if this happens. He also found his bearing remained in the cap, it had pulled off the shaft during removal.

For the second motor I used a vice to separate the parts.

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Method 1. Catches pressed in, cap edge resting on vice jaws before tapping end of shaft with a hammer.

Method 2.   I did not have a puller so drilled a 28 mm hole through a scrap piece of wood 75 x 50 mm. The hole is larger than the metal rotor but smaller than the edges of the plastic cap.

The vice jaws need to open 120 mm, nearly 6”, with this method. Here I used my JML vice.

The shaft does not reach the right hand vice jaw. Clips were released and then the vice tightened. It took a lot of pressure to separate the cap.

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One of the plastic brush housings on motor 2 had melted allowing the brush to rotate.

I decided it would be interesting to try to repair the motor. Subsequently I found the rotor was faulty.  It was still useful to try alternative repair methods on this motor even though the rotor could not be repaired. Some parts may be useful for future repairs.

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Left  Motor 2 damaged brush plate.  

Brush had twisted and fused with the melted plastic, it could not be pulled out.

Right  Housing after restoration.

Most of the brush was chipped away before filling with JB Weld two part epoxy which it is rated to 260 deg c.    

Standard Araldite is only rated to 65 deg C, not suitable for this job.

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Rubbing damaged this impeller and the magnet was lost. Replace it with a neodymium magnet the same diameter glued into place. Standard Araldite is only rated to 65 deg C. I would use JB Weld two part epoxy, 260 deg C, or similar.