Polaris Trail boss defies logic
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Polaris Trail boss defies logic
Hey All, Maybe you can help me, I run a small engine repair business in western mass, and recently took in an 89 polaris trail boss 250 in trade for a compound bow. The machine hadn’t run in what id guess was a year or 2, and was in bad need of a top end I proceeded to dismantle the engine purchased a top end kit .40 over and took the jug to a very reputable auto machine shop to be bored and honed, put the engine back together did a thorough carb cleaning, and tried to fire it up, nothing, ok so I took the spark out, perfect spark, strong, spanning almost a half inch, so I thought it might be a timing problem, removed the flywheel and adjusted the timing plate to factory specs, put it back together tried to fire it up again, and again nothing, not even so much as a sputter. I took the fly wheel off several other times ,trying the timing in multiple positions, and every time i turned the motor over the machine wouldn’t even so much as burp, so i began to test the other components of the ignition system. The exciter coil measured in at right around 120.2 ohms of resistance, which according to factory specs is good, the stator measured at 1.2 ohms, and the ignition coil also at about 1.2 ohms, which I believe is high for these coils but I would still think the engine would do something. The only other thing is the CDI unit, but I have good spark and it’s not often that a CDI unit can go bad and still give spark tell me what you think.
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Crank seals are what most people overlook when doing just a top end. If it's been sitting with gas in the crank case for up to two years, seals can distort and wont hold bottom end crank pressure for the fuel mixture.The seals usually will show signs of leaking when this happens.You have to have a good top end and bottom end compression for the air/fuel/oil mixture to shoot up the transfer ports to fire.. If you're sure the top end is done correctly,spark is good as you say,stator plate timing is correct,plus it won't even try to kick off with starting fluid,then I would suspect the seals.
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Only about 60 psi on both wet and dry test, A bit low Although I am quite confident in the machine shops allowed tolerance, and the cross hatching on the hone looked good. The machine shop I used has been in business for 30+ years building motors for various racing vehicles, they Have high end cnc boring and honing machines.
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Only about 60 psi on both wet and dry test, A bit low Although I am quite confident in the machine shops allowed tolerance, and the cross hatching on the hone looked good. The machine shop I used has been in business for 30+ years building motors for various racing vehicles, they Have high end cnc boring and honing machines.