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I have a small engine inverter generator. This generator is to be used during power outages which happen rarely where I live, and also tested shortly every 2 years (the testing is also to keep the electrolytic capacitors in the inverter healthy, as a non-used electrolytic capacitor can degrade).

The user's manual says these about storing the generator:

  • It should have no fuel inside the tank or carburetor (which I do by letting it starve of fuel, and there's also a fuel drain tube with screw in the carburetor)
  • I should remove spark plug, put a tablespoon of oil into the cylinder and, slowly pull the recoil cord to lubricate the cylinder with ignition off to prevent electric shocks from the loose spark plug wire, and reinstall the spark plug

I will also be doing this, which this generator's manual does not have but many other brands of generators to have this in the manual:

  • I change the oil before storage (which I obviously do since this is the single most important maintenance of an engine)
  • I pull the recoil starter until I feel little bit of resistance (which should ensure the valves are closed)

The main problem I'm having is that the spark plug access cover is way too small. It seems very awkward to even remove the spark plug wire, not to mention fully removing the spark plug. Perhaps the generator was designed by someone with really small hands. So I thought that I might want to skip this step.

How harmful is it if I don't put oil in spark plug hole of a stored engine?

I can imagine at least two problems that might occur:

  • If the generator is stored outdoors, humidity could condense inside the cylinder and cause rust, destroying the engine. However, I won't be storing the engine outdoors, I store it indoors in a heated space, and besides, if I ensure the engine is stopped with valves closed (by pulling the recoil cord until I feel resistance), that should also make it harder for water to condense inside the engine. So rust shouldn't be an issue.
  • When starting the engine, a layer of oil in the cylinder walls could help avoid wear. However, if I expect the generator to work for 30 years, I will have maybe only 15 starts without oiled cylinder walls. Can 15 such starts really damage an engine?

What is the primary reason for the advice about oiling the cylinder walls? Is it to prevent rust, or is it to ensure good lubrication when the engine is started after long storage?

The engine has splash lubrication (no oil pump, no oil filter).

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  • Is it a 2 or 4 stroke engine? 2 stroke could require oil in the fuel either premixed or metered in, which will lubricate the bores nicely.
    – Criggie
    May 19, 2022 at 11:53
  • You could use fogging oil instead. I don’t think any of us can answer the question if wear other than anecdotally.
    – Tim B
    Jun 18, 2022 at 15:11

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It would be best to follow the instructions in the manual. Adding oil does protect the cylinder from rust and also ensure lubrication on first start after a long period of storage. My John Deere lawn tractor manual says the same thing for storing over the winter (5-6 months). There would be some wear on the cylinder wall and piston rings if you did not add oil to the cylinder and the amount of wear would be relative to how long the generator was stored between starts so it would be difficult to determine.

Since the space to access the spark plug hole is tight you might want to use a flexible tube and syringe see below.

enter image description here

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  • I don't think the main issue is getting oil into the cylinder, it's accessing the spark plug wire and spark plug.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 18, 2022 at 15:01
  • Yes, the main issue is getting the spark plug out and reinstalling it. However, the syringe could be helpful in injecting the oil.
    – juhist
    May 19, 2022 at 9:27

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