General 2stroke oil system questions

[skrillac]

I searched around this forum searching for a couple questions I have regarding the engine oil cavity and the oil system in general for older 2 stroke skis.

I've seen videos on youtube of people who pressurize the cavity in order to suck oil through lines to fill the cavity. I previously hooked up a drill pump to the oil line I have marked green here and pulled oil through the line I have marked blue.

I am aware there is a check-valve attached to the oil tank to allow air in. But what stumps me is how oil flows in this system without a pump. Or rather, how oil leaves/enters the engine cavity. It is true air is entering the tank to account for oil displaced into the chambers, but this force isn't significant and presumably leaves the engine cavity drawing oil purely through gravity.

1. Will crankcase pressure internally push/pull oil through the cavity and out through the oil line marked green?

I would like to think it would, because crankcase pressure is also used to operate the fuel pump.


2. I just recently replaced all the oil and oil lines on this ski. Should I expect oil in the line marked green to move upwards and spill over into the tank?

 

[mikidymac]

It is just a flooded chamber filled by gravity. There is no pump or actual oil flow.
The engine is lower than the tank so it is kept full.

 

[skrillac]

@mikidymac

So oil just sits in the cavity lubricating the gears and crank, slowly burning and drawing new oil in from gravity, through the line in blue? Why need an oil return line (line in green) at all? Is it just a breather line?

Also, should I be worried about pulling oil through the line in green (return line) completely, or just through the engine cavity? I'm thinking of a case where I'd need to replace oil if I have an oil leak or need to rebuild the engine again.

 

[mikidymac]

Yes, the oil just sits in the cavity. If your inner crank seals are good and not leaking then no oil would ever be used.

There is no reason to "pull oil through" the line. It is just a vent that lets out any trapped air or pressure as the engine heats and cools. The oil flows from the tank by gravity and any air is expelled out the vent hose so unless gravity stops working the chamber will always be full and self level with the tank.

As long as you have oil in the tank the rotary cavity will be full of oil.

 

[Poormanracing]

The oil is gravity fed the return line is a vent.if it was sealed it would air lock it and not let it feed the cavity

 

[skrillac]

@mikidymac
@Poormanracing

Is it okay to have oil in the return line (green) like I do in the pic above?

 

[Poormanracing]

Yes should have oil level with the oil level in the tank on the hose that runs to the top of tank that's the return