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Discussion Starter · #1 ·
I'm working on a project sled and need to rebuild the engine. A bottom rod bearing blew apart and seized, and some junk got on top of one cylinder and put a scrape inside the cylinder. I tried honing, but it's too deep to and will need to be bored out.

This is my first time having cylinders bored...I know it's idea to have your new pistons available for the shop who is boring the cylinders, but how would I know what size pistons to get if I don't know what size it should be bored out to? I'm assuming the best way to go is to bore as little as possible just to get the scratch out. Stock pistons are 81 mm, so should I just buy 82mm pistons and hope it's enough?
 

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Discussion Starter · #3 ·
Thanks, but what if that isn't enough? I've read that I should have the pistons available for the shop that is doing the bore to reference, but how can I buy them ahead of time when I don't know how much they'll need to take out to remove the scratch?
 

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Thanks, but what if that isn't enough? I've read that I should have the pistons available for the shop that is doing the bore to reference, but how can I buy them ahead of time when I don't know how much they'll need to take out to remove the scratch?
The short answer is that you can't. If the gouges are deep enough the cyl will have to be scrapped. All you can do is either find good cyls or have the shop bore until the gouge is gone and then tell you what they have as far as bore diameter goes. A slow back and forth process, but what can you do? Keep in mind that they will have be re NicaSilled. Not cheap from what I hear.
 

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I scratched up my PTO side Cylinder when I blew a hold in the top side of the PTO piston. Sent out my Cylinder to U.S Crome with the spec's for a new Polaris Piston. Came back looking like a new Cylinder.

The cylinder on the right is the re-built cylinder.

 

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US Chrome or Millenium Technologies will weld the gouge and replate and make 'em look like new. Stegus is right on, it's amazing the damage they can repair. I had really deep gouges in two cylinders, sent them to Millenium with two new pistons, they even fit the pistons to the cylinders for me.
 

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Discussion Starter · #7 ·
Thanks for the help everyone. So the re-plating actually brings the cylinder back to the original size, meaning I could get away with use the stock 81 mm piston and just replace rings on the other good cylinder/piston?
 

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That's what I did. I actually brought the other cylinder to a dealer to confirm it was still ok to use seeing my PTO side was damaged. He said it was in tolerance for a stock piston and new rings.
 

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Piston

I am reassembling my Polaris 700 after a main bearing going bad. I'm honing the nicasil cyliners and installing new pistons. Anyone have any recommendations on pistons? I'd go OEM but they are $120 per piston. SPI are $75. I've heard bad things about Wiseco so I won't consider them. I'm not looking to go cheap, I'd actually like to have the very best piston available. Thanks!
 

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OEM work pretty well in Polaris sleds, the SPI's are a close second. Some guys like Wisecos, but setup is more critical with a forged piston. Proper warm-up also helps. I have used all three and have not had a piston related problem with any of 'em.
 
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