Questions about oil systems in small inverter generator engines

[Indestro]

I know most/all small engines used in the common portable inverter generators are splash lubricated, not pressure lubricated like a car engine. So when the engine is running, the connecting rod will dip down into the oil and splash oil around the crankcase. Eventually oil will get onto the crankshaft, cylinder walls, piston, piston rings, etc. When the engine gets up to operating temperature and the oil thins out, it might even create a fine mist of oil (supposedly).

However, I have never been clear on how good typical splash lubricated oil systems are at fighting gravity and getting oil up into the valve train area. I have heard different ideas, but I came across a video that makes it seem like very little oil, if any, actually makes it up into the valve train area.

This video shows a typical 79cc splash lubricated engine (in a popular Harbor Freight Predator 2000 watt inverter generator) running *without a valve cover* for about 20 seconds. I would have guessed some oil on the valve train would have been sprayed or thrown somewhere. But, not one drop of oil is seen. What am I missing?

Here is the video and the engine runs from about 11:18 to 11:40:



For those who don’t know, the Harbor Freight Predator 2000 watt inverter generator in this video is a clone of a Yamaha inverter generator, and there are at least 5 or 10 companies (including Champion, Generac, Wen, and Westinghouse) that sell an inverter generator that is almost identical mechanically.

I think some of the common 79cc small engines (like the one in this video) occasionally have a small breather tube connecting the valve cover and air intake. I think this might help to pull up some oil “mist” from the lower end of the engine. However, I think a large number of similar small engines do not have a valve cover breather tube. So they are relying on something else to get the oil up to the valve train. What would that be? Does this area actually run relatively dry?

Also, I have noticed that small engines in these Yamaha clones never get hot enough to create a “mist” of oil in my opinion. I have randomly checked engine temperatures of 79cc engines (similar to the one in the above linked video) using a handheld infrared thermometer. The operating temperatures are not high at all (reaching only about 100 degrees F when the outside (ambient) temperature is about 70 degrees F). So the engine oil will stay relatively thick and it will be difficult to get up to the valve train on a normal temperature day. Am I wrong?

I appreciate any thoughts and comments.

Indestro

 

[SC Maintenance]

The “mist” is from mechanical agitation not temperature.

My 196 Chonda generator is horizontal shaft so the OHV is on the side. Maybe that’s better?

 

[Indestro]

The “mist” is from mechanical agitation not temperature.

I agree with you. But the fact that the oil rarely or never gets hot (in these engines) seems like a big problem. It would be like trying to create a mist by agitating maple syrup instead of water.

Indestro

 

[martinq]

I agree with you. But the fact that the oil rarely or never gets hot (in these engines) seems like a big problem. It would be like trying to create a mist by agitating maple syrup instead of water.

Indestro

You need to run the generator, under load, for at least 15 mins before checking oil temperature. You should use a probe in the crankcase to check, use a cooking thermometer or a multimeter probe to check the oil directly. Same with the valve train, check the valve train after the engine & oil is warm for signs of circulation.

 

[SC Maintenance]

You need to run the generator, under load, for at least 15 mins before checking oil temperature. You should use a probe in the crankcase to check, use a cooking thermometer or a multimeter probe to check the oil directly. Same with the valve train, check the valve train after the engine & oil is warm for signs of circulation.

Yes, I agree. I have drained my generator hot and there was no way it was only 100F.

 

[repairman54]

Valve cover off will disrupt the internal ''air flow'' of the oil mist in the engine. Most likely the design engineers made a cover with a window to observe oil flow. Back side of the piston acts as an internal air pump. Ever run one without the oil cap / dipstick on and watch oil get pumped out like on a Tecumseh or Briggs. Cold or hot oil it will blow some out.
Lower oil temp is good IMO, less thermal breakdown and the reason multi viscosity is specified to cover all possible oil temps in varying conditions.

 

[Indestro]

You need to run the generator, under load, for at least 15 mins before checking oil temperature. You should use a probe in the crankcase to check, use a cooking thermometer or a multimeter probe to check the oil directly. Same with the valve train, check the valve train after the engine & oil is warm for signs of circulation.

I forgot I had done some of this before. My notes say on a day when ambient temp was about 55 deg F, the probe said oil temp was about 135 deg F. That's a food temp probe in the oil fill/drain hole right after turning off the generator (after it warmed up completely).

I never checked the valve train because it's harder to access the valve cover and remove it, compared to just sticking a temperature probe in the hot oil.

I appreciate all the thoughts and comments.

Indestro