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Old 07-31-2009, 03:04 AM
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Piston direction on 2-stroke

Picked up a disassembled Polaris Xplorer 300, engine was completely torn down by the PO and I'm going to start on it today after work. Its a 2-stroke engine with oil injection. Since it doesn't have a cam or any valves, I'd imagine the piston is directional to allow the piston skirts to line up properly with the intake and exhaust, correct? Any tips on what to look for? I bought a service manual; but it does not specify. TIA
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Old 07-31-2009, 06:49 AM
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The ring pin that centers the ring on the piston will face to the intake side of the motor. Good Luck!
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Old 07-31-2009, 07:33 AM
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Sounds like FUN!
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Old 07-31-2009, 07:44 AM
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Two strokes are always fun!
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Old 07-31-2009, 09:48 AM
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Alright, that makes it easy enough.

Now a question I'm ashamed to ask; but be easy on me as I've only ever rebuilt car/truck engines. This is my first 2-stroke project. What kind of lubrication does the crank case take? The manual lists engine oil for the 4 stroke engines; but says nothing about lube for the 2 stroke crankcase. There's bearings down there... that tells me there must be fluid! Funny how an engine way less complex than what I'm used to dealing with is making me feel like a complete novice.
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Old 07-31-2009, 10:51 AM
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The oil from the injection pump will lube the bottom end. use a good synthetic oil not the Polaris stuff. Make sure you lube all bearings lightly on reassembly and use 1104 Three Bond to seal the crankcase. Make sure to break loose the bleeder screw on the oil pump and bleed out any air in the system. Good luck!
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Old 07-31-2009, 07:58 PM
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2 stroke pistons have an arrow on the top of the piston, the arrow always points to the exhaust side, or forward, the oil pump provides the mix for the 2 stroke, if the pump is being bypassed, mix the gas at a 32:1 ratio, i had to do this with my old 87 cyclone
hth
Rick, Ore
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Old 08-01-2009, 07:22 AM
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Yes what you say is true to some point but it depends on the manufacture what way the arrow points so do not use that as a guide. The 32.1 mix will work on the first tank then switch to 40.1 or just run Amsoil 100.1 premix this is real good stuff. Yes you can mix it at 100.1 as we have mixed at 180.1 in drag sleds with over 300 hp with no failures.
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Old 08-10-2009, 11:27 AM
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Finally got a start on this over the weekend. With the arrow on the piston pointing toward the exhaust side, the "pins" for the piston rings are facing towards the intake side; so I assume that's a good sign. Got old bearings and seals replaced with new, put the new crank in, and mated the two halves of the crankcase. Couldn't get any further than that as one of the piston wrist pin retaining clips is missing.

I guess I still don't completely understand (or maybe trust) how the bottom-end stays lubed if the crankcase isn't filled up with 2cycle by the oil pump. It makes sense for the bearing on the flywheel end near the pump; but the bearings on the other end of the crank and the little needle bearings on the piston wrist pin are a good distance away from there. I did put a light coat of oil on everything while assembling.

Oh, and BTW, when I cleaned up the crank case, it had 241cc and the mfgr name machined into it. I could justify calling a 241cc motor a 250... but Polaris is pretty ambitious passing it off as a 300. LOL
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Old 08-10-2009, 12:22 PM
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The bottom end will be fine. The crank and case for the 250 and 300 are the same that is why they have the 241cc stamped on it. The top end is what is different.
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