Some 1-cylinder small engines have instructions that before long-term storage you should take off the spark plug, pour few milliliters of oil into the cylinder, and very slowly pull the starter cord (with fuel supply and ignition off) to lubricate the cylinder with oil, and re-install the spark plug.
My inverter generator is one of those where the instructions say that. Unfortunately, the manufacturer has made the spark plug access port so small that I can't with my large hands reasonably change the spark plug without dismantling lots of the covers of the generator, which would take so much time that I have decided instead to not do the "oil in spark plug hole" trick.
I have an alternate plan which might provide some of the benefits (namely, improved lubrication, not improved rust protection), without requiring so small hands that it's possible to reach the spark plug through the small access port.
The plan is to run the engine out of gasoline before long-term storage (which would be advisable in any case, since old gasoline can gum up the carburetor, and also fuel lines can deteriorate if they are constantly full of gas). Also before storing the engine, the starter cord should be pulled until you feel you are in the position where there starts to be a little compression (so the engine is stored valves closed, to give at least little rust protection). Then when re-starting the engine after a long-term storage, the plan is to fill it with gas, move it to the operation area, and do few rapid pull starts with choke valve off, fuel supply valve off, and ignition off:
- The fuel supply valve would be off to avoid recently filled gasoline getting in to the engine.
- The choke valve would be off, in case there still was gasoline in the carburetor, which could flood the cylinder if choke valve was on
- The ignition would be off, in case there still was gasoline in the carburetor, which could start the engine so fast that the few pulls of the start cord wouldn't distribute oil before engine is started
The idea here is that since this is a splash lubricated engine, few rapid pull starts should rotate the engine enough that oil is splashed around, and hopefully oil would coat the cylinder wall due to those splashes.
I have read that typical gasoline engines have about 7-10.5 MPa peak cylinder pressure. On the other hand, a 9:1 compression ratio engine would have
9^1.4 = 21.674 times air pressure without ignition (where 1.4 is the ratio of specific heats), which is about 2.2 MPa, far less than peak cylinder pressure. So theoretically the forces on the piston should be much smaller without ignition but with compression, which should mean the cylinder wall should be coated with oil with less wear than there would be if there was fuel and ignition. Then when the engine is finally started, lubrication would be already assured during the first fractions of a second.
I understand that hybrid vehicles can do something similar. They don't have a conventional starter motor and a small battery but rather a more powerful motor/generator and a big battery that could rotate the engine for tens of minutes at least at any speed. So they can rotate the engine at idling speed, wait for oil pressure to stabilize and for oil to coat all parts of the engine, and only then inject fuel and start ignition.
Does this idea make sense? Or is the rotation of crankshaft during pull starts so slow that oil doesn't splash efficiently enough?