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post #31 of 35 (permalink) Old 10-06-2011, 04:33 PM
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Cool! I've never worked on a two stroke atv before, totally different world than I'm used to with 4 strokes. I always wondered how a 2 stoke oiled the cylinder wall, thinking the air fuel mix came in through the intake valve like a 4. While cleaning the carb on a junk leaf blower I looked through the intake and saw it sucks it the a/f/o mix under the piston, past the ring(s) (don't know how many it has?). That just blew my mind, lol. I've been trying to learn some more about them, maybe I can get my hands on one next year to learn...
Feel free to come and work on the S.O.A.B. that I'm working on at the moment, a 350 2-stroker with a knackered water pump, it's a very tight machine to work on!!!!!!!!!!!!!! For your info, there are two compressions on a 2-stroke single cylinder, as well as your combustion chamber compression, the crank case also must retain airtightness so as the piston comes down on the power stroke so it compresses the fuel mix until the inlet port is exsposed, the fuel mix is blown under pressure into the cylinder , driving out the exhaust gas's. The fuel mix won't blow back into the carb because the piston skirt close's , on it's downward stroke, the inlet from the carb. Depending on the fitment, the carb can be mounted on the cylinder or on the crankcase. When crankcase mounted, the inlet passage from the carb is sealed on crankcase compression by reed valves. On large Diesel engines the air is compressed by turbochargers and scavenge pumps ( A large supercharger) not into the crank case but into scavenge spaces along the side of the engine and exhausts through a single exhaust valve on top of the head. these engines are can be very big ,developing 7,500 HP per cylinder and up to 14 cylinders. Check them out on u-tube under 'large ship engines'
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post #32 of 35 (permalink) Old 10-06-2011, 04:46 PM
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nice work!!


with the incorrect oil to gas ratio, not enough oil to be specific, think it would more so effect the crank bearings or rings?? if it still turns over freely could that rule out bearings??
I think you'ed find more damage on the thrust side of the piston and cylinder wall, with the bearings seldom affected, with difficult starting and fuel escaping through the mouth of the carb ( Crankcase compression escaping because of the damaged piston).
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post #33 of 35 (permalink) Old 10-06-2011, 07:23 PM
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nice work!!


with the incorrect oil to gas ratio, not enough oil to be specific, think it would more so effect the crank bearings or rings?? if it still turns over freely could that rule out bearings??
I think you'ed find more damage on the thrust side of the piston and cylinder wall, with the bearings seldom affected, with difficult starting and fuel escaping through the mouth of the carb ( Crankcase compression escaping because of the damaged piston).
that seems like how it acts. thanks. sleeve and rings for replacing?

88' 300 fourtrax 2wd
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post #34 of 35 (permalink) Old 10-07-2011, 04:11 AM
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nice work!!


with the incorrect oil to gas ratio, not enough oil to be specific, think it would more so effect the crank bearings or rings?? if it still turns over freely could that rule out bearings??
I think you'ed find more damage on the thrust side of the piston and cylinder wall, with the bearings seldom affected, with difficult starting and fuel escaping through the mouth of the carb ( Crankcase compression escaping because of the damaged piston).
that seems like how it acts. thanks. sleeve and rings for replacing?
Is the sleeve scored in any way? you might have some pick up from the piston stuck to the sleeve but this can usually scrapped off (depending on how long it was run on wrong fuel /oil mix). Is the piston damaged? If it is, a new piston assy. is required (complete with rings and gudgeon pin) also measure the piston diameter against the original spec. To evaluate sleeve wear take a ring of the piston and fit it into the very top of the sleeve ,measure the gap, move the ring down to the firing area at the top of the stroke, measure the gap, and finally repeat at the bottom of the stroke, any difference in the gap would suggest that the sleeve is past it's prime. Is the quad a premix or autolube?

Last edited by toyota; 10-09-2011 at 01:26 PM.
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post #35 of 35 (permalink) Old 10-08-2011, 08:50 AM
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gracious.

primix, i wasent measuring it out in a cup, just guessing on the oil amout (learned my lesson on that one) fubared a dirt bike and a chiansaw. they were both ran to they seemed like they lost compession and died.

i have not tore into either one yet, i have no experice with 2 stokes or even knew how they worked till i saw that picture diagram somewhere on here. think ill tear into the chainsaw first, its a cheap one anyways. ha.

88' 300 fourtrax 2wd
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