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Old 11-04-2007, 08:36 AM   #1
Chris24
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why do 2stroke and 4 stroke lube differently?

ok to you guru's out there: (jetcycles, patrick)

i couldnt sleep the other night and i was thinking over in my head the difference between 2 stroke and 4 stroke (yes i have issues), going over each step in my head and also all the parts of the engine.

ive known the difference for a long time, but i dont know, for some reason it started making alot more sense, and i knew why things were, not just that they were.

at first i couldnt think of a reason why 2stroke uses different oil and does not lube itself like a conventional 4stroke. now the only reason i can think of is excess heat? since a 4s combusts once out of every 4, it has three to cool, whereas a 2s can only cool once every other stroke? not enough? the excess heat would just cause too high rate of failure and wear on components (which they do anyways somewhat)

any other reasons?

i think i want to be an engineer when i grow up
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Old 11-04-2007, 09:25 AM   #2
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Good question.
Maybe part of the answer is simplicity. Since a 2 stroke doesn't need oil up in the head to lube valvetrain components, why bother with a wet sump/ oil pump setup?
Of course newer 2 strokes have an oil injection pump, that may be more for convenience than anything else. (No mixing oil and gas)


other ideas?
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Old 11-04-2007, 09:40 AM   #3
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Quote:
Originally Posted by bumblebee View Post
Good question.
Maybe part of the answer is simplicity. Since a 2 stroke doesn't need oil up in the head to lube valvetrain components, why bother with a wet sump/ oil pump setup?
Of course newer 2 strokes have an oil injection pump, that may be more for convenience than anything else. (No mixing oil and gas)


other ideas?
+1

It's just easier/cheaper to make an engine without all the oil injection . The four stroke would destroy itself quickly if you did this though due to the extra cycles. I would think that the oiling injection system on a two stroke would have a power robbing effect on the motor as well considering those are extra parts to turn. Main reason why most racers ditch the factory installed oil injection system on two stroke race bikes in favor of premix, ie. NSR250.

Last edited by Scorpio; 11-04-2007 at 09:43 AM.
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Old 11-04-2007, 08:43 PM   #4
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a 2 stoke needs the crankcase to move it charge therefore can't have oil in the crank case. The 4 stroke uses oil in the crankcase because it doesn't need to move a charge in there.

exceptions a 2stroke diesel is high pressure FI therefor does not need to move the charge in the crankcase so it has oil in its crankcase.
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Old 11-05-2007, 01:04 AM   #5
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with pre mix lubricating method, as fuel circulates from primary area under the piston to secondary area above pistone oil travels with it, lubricating the cylender. an oil injected method uses an oil pump that squirts oil into the intake manifold as the fuel is entering the cylender, so the difference there is when fuel and oil mix. four strokes dont use either of these methods cause fuel is not moving from primary to secondary fuel and air mixture enters through valves most of the time above the piston, in two strokes the mixture enters through holes in the side of the cylender
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Old 11-06-2007, 08:18 PM   #6
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Quote:
Originally Posted by AZ slide View Post
with pre mix lubricating method, as fuel circulates from primary area under the piston to secondary area above pistone oil travels with it, lubricating the cylender. an oil injected method uses an oil pump that squirts oil into the intake manifold as the fuel is entering the cylender, so the difference there is when fuel and oil mix. four strokes dont use either of these methods cause fuel is not moving from primary to secondary fuel and air mixture enters through valves most of the time above the piston, in two strokes the mixture enters through holes in the side of the cylender
yes in a nut shell if the fuel didn't have oil in it the gas would wash the oil off the cylinder and bang piston seizes.
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