Background
My mothers neighbour's lawn mower stopped working recently. She has had it for many years and stored it in an outside shed that was not particularly well weather tight. That did not stop it working year after year. The date code on the rating plate indicates the mower was manufactured in 1981. She asked if i could have a look at it to see if it could be repaired or tell her if it was time to invest in a new one.
To be honest when i examined the mower it was showing the signs of its age. However i had seen it used many times and it operated efficiently and smoothly and did a good job cutting the grass so i thought it was worth considering fixing if the costs were not too high.
I set about finding the fault. I checked the fuse but it was intact. I checked the mains cable and found an area that had been repaired with insulating tape. The insulating tape was removed to check what kind of damage it was covering. Although the copper wire was exposed inside the neutral it was intact. The switch module was dismantled and inspected. It was found to be operating normally.
This left the motor housing and wiring from the control switch to the motor. The motor housing was removed and what was found was quite shocking. How the mower had survived so long was quite incredible. Below is a record of the work performed to repair the mower and get it back into service.
To be honest when i examined the mower it was showing the signs of its age. However i had seen it used many times and it operated efficiently and smoothly and did a good job cutting the grass so i thought it was worth considering fixing if the costs were not too high.
I set about finding the fault. I checked the fuse but it was intact. I checked the mains cable and found an area that had been repaired with insulating tape. The insulating tape was removed to check what kind of damage it was covering. Although the copper wire was exposed inside the neutral it was intact. The switch module was dismantled and inspected. It was found to be operating normally.
This left the motor housing and wiring from the control switch to the motor. The motor housing was removed and what was found was quite shocking. How the mower had survived so long was quite incredible. Below is a record of the work performed to repair the mower and get it back into service.
At some time in the past it looks like the mower blade had struck the mains supply cable damaging it, exposing the copper cable inside.
The cable had been repaired with electrical insulating tape.
I decided to cut out the 1.5 meter length between the damaged area and the mains plug. There is still plenty of cable to allow the mower to be used easily.
When the motor cover was removed this is what was found! The motor had sucked in the grass cuttings over the years creating this matted cover surrounding the entire motor. None of the major parts of the motor structure were visible because of the grass cuttings.
Most of the grass cuttings were easily removed. The more embedded cuttings had to be loosened from the chassis and sucked out with a vacuum cleaner. This picture shows that the carbon motor brush is still in contact with the commutator but the locating wrap spring is at the end of its travel.
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This view shows the motor with one of the carbon brush mountings just visible. The grass cuttings were quite densely packed and very dry. I was surprised that they had not caught fire at some point. I suspect that once the motor housing was packed with cuttings this started to act as a 'filter',replacing the missing foam filter, stopping larger, harder objects from being sucked into the motor.
This picture shows the other motor brush. Here it is clear that it is no longer in contact with the commutator and the locating wrap spring is pressing against the end stop. This would explain why the mower was not working. The carbon brushes have worn away with use and need to be replaced.
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This picture shows the motor cleaned up to allow its major components to be examined.
The bearings were still operating smoothly and the stator and rotor winding were in good condition. All the electrical wires and connections appeared to be in good condition.
The exploded parts diagram was downloaded from the manufacturers website. This revealed what was suspected when the motor cover was removed, that a filter to prevent grass cuttings being sucked into the motor was missing. The filter fits into the outer space surrounding the motor and is held in place by fins on the inside of the motor cover.
Unfortunately the filter is no longer available as a spare part so some other solution will have to be found.
Replacement carbon motor brushes were purchased on-line and took just a few days to be delivered.
This photograph shows just how much wear has occurred over the 36 years(1981-2017) of use.
The upper and lower brushes are the new ones, the middle is one of the original brushes.
Here the brush has been fitted into the holder, connected to the spade terminal and the brush locating spring mounted into the slot on the rear of the brush.
The locating springs were oiled to slow down any further corrosion.
The other spring snapped when it was moved into position at the rear of the brush due to the corrosion. I was able to partially unwrap some of the spring to create sufficient length to reach the brush.
As the foam filter was no longer available as a spare part i had to come up with an alternative solution.
Initially i looked at using small cleaning sponges cut to size and glued together, but testing with a vacuum cleaner showed that they were too dense and restricted the air flow.
I located sheets of automotive air filter foam on-line and ordered these. They were cut to the required size and installed in the slot. An overlap at both sides was provided to ensure that there were no gaps to allow grass cuttings to get in.
The repaired 36 year old mower ready to re-enter service after a short 'holiday'.
The following work was performed:
1. Repair damaged mains cable.
2. Locate, order and install new motor brushes.
3. Locate, order and install replacement air filter foam and shape to fit.
4. Clean out old grass cuttings from motor and housing.
The total cost of replacement parts was just less than GBP12 and cleaning, repairing and ordering parts took about 2.5hours at most.
A job well worth doing to save a fine old mower from the recycling yard for a few years at least....here's to the next 36 years!