Need help-polaris 850 engine won't spin once crankcase half torqued down - Polaris ATV Forum
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post #1 of 8 (permalink) Old 04-29-2019, 03:01 PM Thread Starter
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Need help-polaris 850 engine won't spin once crankcase half torqued down

So I'm in the middle of rebuilding my buddies 2017 850 sportsman engine. It ingested water, he thought he got all of out but didn't, engine didn't sound right, so he shut it off and pulled it out. I took the engine apart, had some scuffing on the pistons, and the main bearings looked bad, and crank was scored. So I got a new crank, and bearings. Reassembled the engine, spins freely. As soon as you torque down the bottom crankcase cover it doesn't spin, and feels locked up. It didn't spin a main bearing or anything like that when he had the issues. So what am I missing?? Thanks!!
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post #2 of 8 (permalink) Old 04-29-2019, 07:06 PM
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So, I'm not sure if this can cause the problem, what color crank bearings did you put in? I'm not entirely sure how to judge which bearings to order? I'm guessing it's based off of the crank diameter? Is it possible the color bearings you ordered are to small? I'm just throwing out ideas. Not sure if it can cause the problem.
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post #3 of 8 (permalink) Old 04-30-2019, 03:05 AM Thread Starter
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Bearings Came with the crank for the mains.
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post #4 of 8 (permalink) Old 04-30-2019, 08:31 AM
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The bearing shells are different for the center than the ends - maybe you got them mixed up?

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post #5 of 8 (permalink) Old 04-30-2019, 10:35 AM Thread Starter
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Center bearings have full grooves in them, outers don't, and the bearing tangs are in different spots so they don't swap around. As soon as I snug the case cover down it binds. I even disassembled the whole short block again, and am just testing it with just the crank
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post #6 of 8 (permalink) Old 04-30-2019, 01:43 PM
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Makes you wonder if the case main bearing bores are not concentric with each other. Have you tried just 2 bearings at a time, maybe remove the center main and see if rotates or changes at all, or the center main and one outer. I'm sure you looked at all the obvious things , dirt, burrs ect.

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post #7 of 8 (permalink) Old 04-30-2019, 06:39 PM
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Plastigage the bearings on various axis

2006 Trailboss 330
2002 Sportsman 90
2005 TRX400EX (FOR SALE)
2003 LT-Z400 (needs engine work & is for sale)
2004 CRF250X
1971 Triumph 650 Bonneville (has 5 original miles)
1972 Triumph 650 Bonneville (undergoing restoration)
1979 Honda CBX (6 cylinder)
1970 Kawasaki G3SS 90cc Bushmaster
1976 Suzuki RE5 Rotary (not running & FOR SALE)
1981 Kawasaki KZ305-A
1981 Suzuki GS450T (undergoing repair & will be for sale when done)
1982 Kawasaki KZ750-H (FOR SALE)
1989 Honda VT1100C
2007 Vectrix VCTX Electric Scooter
1965 Montgomery Ward 3 1/2 HP Tecumseh Mini Bike
1970 Triumph T25 250cc Trailblazer
1968 Triumph 250cc Flat Tracker

Shop Owner and Mechanic with over 50 years experience
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post #8 of 8 (permalink) Old 05-01-2019, 04:09 AM Thread Starter
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I put the bearings in last night again, scotchbrited the bearing bores before install, torqued down the case halves and used a telescoping guage and measured the inside bore with the bearings installed, it comes out that the bore size is .001 under on the stator side bearing??? I don't get it, this engine never spun a bearing. One thing I do notice, with the bearing shells installed they stick up slightly from the case halves, when fully pushed down?
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