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2 Stroke Lubrication. How does it work?
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Posted by: SndyRds
Hi, all.
I've heard two theories on how a 2 stroke bottom end gets lubricated.
1. Oil stays in suspension in the fuel, and "mist" lubricates the crank, and rod.
2. The oil comes out of suspension from the fuel, and pools in the bottom of the crankcase, and uses, the "splash" method which seems counter intuitive, as centrifugal force would fling the oil outward.
I ask for a couple of reasons. First I've never torn down a 2 stroke engine and found oil pooled in the crankcase.
I've also seen enough spooge (oil separated?), that it comes all the way to the silencer, (obviously bad jetting, not my bike).
And an unusual occurrence with my own bike: A 1999 KX250 jetted spot on no spooge, almost no smoking on start-up. Using Mobil syn 2 stroke oil 40:1. I had been doing a lot of tight slow single track riding for a couple of weeks, and on the next ride, after about 30-40 mins. into the ride I had the bike wound out in top gear fairly hard in a fast sand wash. The exhaust belched out white smoke for about 50 yards. No evil sounds, or loss of performance. Then as mysteriously as it started it stopped.
The bike ran fine the rest of the day, and it never happened again.
Also if the oil stays in suspension, it lubes the top of the rod, and piston, through the ports.
It throughly amazes me that a oil/fuel lubrication mixture (such a low viscosity) holds up to the shear forces,at the crank, obviously nothing like those, at a cam or trans gear.
I guess those needle bearings are pretty magical.
Your thoughts/data?
Thanks, Sandman
Posted by: cujet
There used to be quite a bit of discussion about 2 stroke oil coming out of suspension and migrating around inside the crankcase.
In particular it was noted that it would remain on the con rod intact (not wash off). Certainly it comes out of suspension where the fuel can evaporate quickly.
I truly have no idea what really happens, but I have seen plenty "O" oil in the crankcase bottom at the end of a ride. Sometimes, so much so that turning the crank over bathed it in oil!
The smoke you noticed occurs in the pipe. Generally, 2 strokes can get the pipe up to a temperature high enough to vaporize the remaining oil. Sometimes, it can continue forever at high loads, a 2t streetbike might do this when run flat out for miles. This can be tuned out in most cases. I suspect that the formation of thick acrid smoke is not detrimental to the engine.
Chris
Posted by: Isobareng
1. Oil stays in suspension in the fuel, and "mist" lubricates the crank, and rod, piston skirt, rings,
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