15 SP850 Rebuild - Polaris ATV Forum
ATV Repair and Maintenance Having problems? Doing a rebuild? All Repair/Maintenance Discussions here.

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post #1 of 7 (permalink) Old 06-27-2018, 11:46 AM Thread Starter
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15 SP850 Rebuild

Picked up a 15 SP850, all stock. Only has 72 hrs on it. Guy says it backfired then quit running, then wouldn't start. Check compression, rear cylinder was good but front cylinder had 0psi, none. So I Pulled motor, started the tear down, The top of the piston above the top ring has broken apart, causing some damage to the cylinder head, not sure if theres somewhere that it caan be repaired or not as its not cracked or has huge gouges in it. The rear cylinder that had good compression has part of the top of piston broken too.

Few questions:

1: how to tell if the cylinders are nickasil? Dont you just stick a magnet to it and if it sticks its iron?

2: Posted pics of combustion chamber of cylinder head with damage, anywhere that could possibly repair this instead of buying new or good used head?

3: Is it completely necessary to pull flywheel to split case? Ill order the special tool if i have to I just dont see why it would hinder the bottom end coming off
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post #2 of 7 (permalink) Old 06-27-2018, 11:51 AM Thread Starter
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Closer pic of head
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post #3 of 7 (permalink) Old 06-27-2018, 11:54 AM
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I'd talk to the guys at Nflow. They are supporting vendors of the forum.

https://www.nflowmotorsports.com/pro...tured-engines/
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post #4 of 7 (permalink) Old 06-27-2018, 12:15 PM
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stompermotorsports, give us a call here at nFLOW Remanufactured Engines at 812-402-8282 and ask for Corey. He can go over the options and details. Thank you for the recommendation polman500. www.nflowmotorsports.com
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post #5 of 7 (permalink) Old 06-27-2018, 12:46 PM
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Quote:
Originally Posted by nFLOW View Post
stompermotorsports, give us a call here at nFLOW Remanufactured Engines at 812-402-8282 and ask for Corey. He can go over the options and details. Thank you for the recommendation polman500. www.nflowmotorsports.com
Be kinda' nice if we could see the options too...

Matthew "MustBeNice"

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post #6 of 7 (permalink) Old 06-27-2018, 01:12 PM Thread Starter
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Well got it apart, cylinder is scarred from the broken piston. Sucks butt. J.E pistons offers a bbk but only for the nickasil cylinders, pretty sure this one is steel. New upper case half is $1500 alone.
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post #7 of 7 (permalink) Old 06-27-2018, 01:46 PM
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So, a buddy of mine just ran into the same problem. He purchased a 2015 850 and his cylinder head, walls and pistons were all messed up. He ended up sending the top out to have the cylinders replated. He put namura pistons in. The shop told him which size to go with since it was oversized a bit. Now he needed a special tool to remove the fly wheel. He was unable to purchase or rent the tool. He ended up purchasing the piece that goes into the water pump housing and welding an adaptor to it so he can remove and install the fly wheel bolt. I will try and get details on who he went through to get the cylinders replated.
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