Re: Unburned Fuel collection

[Pete]

quote ryanjames170:

So if I might ask a dumb one how dose the oil gas mix get into these drains? Ie with out creating a rather large pressure leak in the crank case?

The excess mostly oil mix collects at the bottom of the crankcase and with the gravity and positive crankcase pressure pulses the oil mix is forced thru a small orifice and into the lower unit housing. The orifice is small enough to cause little operation effect. On 2 cycle engines the higher the revs the less residual to be collected since most of the oil fuel mix gets to the cylinders especially at full throttle. On my 2 cylinder 70’s era Merc engines the design included an oil residual collection system that crankcase positive pressure pulses pumps the extra residual oil mix to the top bearings where extra lube is always needed, there is a check valve in the system to prevent reverse flow during the crankcase suction pulse phase. Earlier Merc and probably other brand ( :?:) engines had a small hole drilled in the lower crankshaft seal and the positive pressure pulse forced the residual out the lower unit.