Generator servicing decoded

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What is involved in a generator service?
The Oxford online dictionary offers the following:

“A periodic routine inspection and maintenance of a vehicle or other machine”

For most folk the idea of a service conjures up images of wise old technicians in half-framed glasses making meticulous measurements and adjustments. Often the reality is an oil change and new spark plug fitted by the runner-up of Britain’s Got Acne.

Listed below are things that ought to be considered as part of a service. Not all will be relevant for every machine and some items will not require attention at every service. Service intervals vary from machine to machine but typically are 100 to 200 hours.

1) Check the oil

Always the first operation before even starting the machine.

2) Load test

You can’t tell much about a generator until you have tested it under load, this should be done at the beginning and end of every service. Load testing gives an understanding of how the generator engine is performing and the output it is achieving in terms of voltage and frequency. Shock loading reveals how well the engine and governor mechanism are interacting to minimize voltage fluctuations. An oscilloscope gives an indication of how the electrical elements compare to other machines of the same type. An oscilloscope also helps assess how well inverter type generators are responding. They are difficult to assess by simply monitoring engine speed and voltage but will reveal a slightly struggling engine through raggedness in the tips of the sine wave and slight voltage fluctuations.

3) Clean and inspect

The physical contact of wiping and polishing will reveal loose or broken parts that might otherwise go undetected. Generators are dependent on an uninterrupted flow of air through the engine and alternator. Dirt, dust, mouse nests, gremlins and debris conspire to impede the flow of air.

4) Oil change

Involves running the machine under load and then immediately afterwards, draining the oil whilst it’s still hot and agitated. A cold oil change distills dirt in the bottom of the engine. The oil must be of the correct grade. For most Honda portable generators this is SAE30 high detergent mineral oil. The most common version of SAE30 oil is that used in lawnmowers and is specifically low detergent. SAE30 HD is less widely available and so 10w40 semi synthetic oil is commonly used as a more available alternative. Synthetics tend to contain more effective detergents than mineral oils. If the machine has been run on mineral oil you may want to run a few flushing cycles to clear the muck that was previously stuck to the sides the engine and will be released by the more effective detergents in semi synthetic oils. Most Honda generators don’t have oil filters so any muck in the oil is constantly re-circulated. For those that do have filters, like the Honda EX5500, EX10D etc then the oil filter will need to be changed.

5) Spark plug

An inspection of the spark plug offers insight into the overall condition of the engine and, while it’s out, one may as well renew it. A spot of copper grease on the threads of the plug will make it easier to remove at the next service. Some machines have difficult access to the spark plug and care must be taken to avoid cross threading. Particular care must be taken with the Honda EU26i and EU30is. Other machines like the Honda EU10i offer ample opportunity for disaster by dropping the plug inside the engine shroud, at which point it becomes a potential destroyer of the flywheel.

6) Cleaning the air filter

Foam air filters on most Honda generators are washable and simply require washing, drying and impregnating with a thin smear of oil. Paper type air filters will need to be replaced. Honda foam air filters are made of an ingenious fire retarding material and so saving thruppence by using a bit of bath sponge is not such a great idea.

7) Clean and inspect slip rings and brushes on AVR controlled machines

The alternator brushes gradually wear away over time. Inspection will reveal their condition so they can be replaced before they become too worn. Brushes at the end of their travel cause arcing between the brush and the slip ring resulting in damage to the slip ring surface. If the slip ring is oxidized or dirty then it can be cleaned with crocus paper or Brasso.

8) Clean petrol tank, sediment traps and fuel filters

The process varies from machine to machine. On some it’s a very simple matter to unscrew the sediment trap on the petrol tap and wash it out. On a machine like the Honda EU30is cleaning the sediment trap requires removal of the air filter housing to gain access. Flushing the petrol tank removes the detritus filtered out by the petrol tank filter and clears the tank of water that accumulates in the lowest parts of the tank.

9) Check the valve clearances

An experienced ear can often spot an excessive valve clearance from 20 feet away by the ticking sound it causes. The same cannot be said for a valve clearance that is too tight so it’s important to get in there and check the clearances while the engine is cold.

10) Carburetor clean?

Not strictly a service activity but well worth doing. If a carburetor is particularly dirty then it will probably reveal itself at the load test stage through hunting or low power. Even if there are no indications, its good form to remove the float bowl and inspect its contents. If it’s dirty or has any yellow-brown staining, then off with the carburetor for a full ultrasonic in Pete’s carburetor jacuzzi.

11) De-coke

This can usually be achieved as part of the final load test by applying the maximum rated load to the machine for at least 30 minutes. This gets the engine and exhaust really hot. After a while bits of carbon start to be ejected from the exhaust as they are burned out of the engine and muffler. You usually end up with a pile of soot on the floor behind the machine. When the particles cease being ejected from the exhaust the engine will be as de-coked as it’s possible to get without removing the cylinder head. This must be done whilst closely monitoring the performance of the engine. Applying full load to a generator that is under-performing can do more harm than good.

12) Check the security of the electrical connections and the integrity of the earth connection

The main power connections experience both the physical stress as appliances are plugged and unplugged and stresses resulting from expansion and contraction as they heat up and cool down so it’s very common for them to get a bit loose. Checking for a good earth connection and good isolation of the earth from the outputs is essential for electrical safety. Any machines that have been referenced to earth (i.e. earth and neutral connected together) should be clearly marked as such. On inverter type generators it’s a good idea to unplug the main blue plug to the inverter pack and ensure all the pins are clean and the spade terminals are a tight fit.

13) General overview

It’s time to just look and listen and think about the whole machine without being constrained by a check list. Like the one above.

14) Tea and biscuits

Without tea and biscuits what’s it all about?

Carb cleaning

Probably the most common Honda generator and Honda engine fault is hunting, low power or poor starting due to a dirty or contaminated carburetor. Even if the engine appears to run smoothly, narrowing of the jets can result in reduced engine power, putting strain on the generator’s electrical elements. Contamination is usually the result of fuel degradation during storage, leaving a smooth coating of fuel residue within the carburetor. This residue is not soluble in petrol and will never just go away. Carburetor cleaner aerosols are no better than snake oil. Air blown through the jets with an airline would be best saved for cooling porridge. The only way to properly clean a contaminated carburetor is to strip it and immerse it in an ultrasonic bath filled with an appropriate cleaning agent. Even some ultrasonic baths will be ineffective at cleaning very small Honda carburetors. The limit of hole size that the cleaner can effectively penetrate is a function of the cleaner’s operating frequency. Cheap ultrasonic cleaners which work well on jewelry will be entirely useless for penetrating the tiny holes within a small carburetor.

I offer a postal carburetor cleaning service using a top specification ultrasonic bath designed specifically for small engine carburetors. This service costs £35 including return post for most Honda carburetors. If you need advice on how to remove your carburetor for cleaning then please call me first.


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by Peter Noble