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Discussion Starter #1
So a while back I let a "friend" use my 400. Well recently it was returned not running. Upon tearing it down found out the piston has a chunk out of it. In all of my past 2 strokes I've always just sleeved and tossed in an over bore piston in and was good to go. but with these its a bit more pricey. called around to a bunch of local shops today and they said they don't do sleeves they just bore the original jug. has anyone just went this route and does it work/ reliable? or does anyone have a good jug to sell?
 

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Re-boring and installing an oversize piston can be done, and when done properly, is just as reliable as stock bore....but it all depends on how deep the damage is. You can only over-bore so much. These limits are listed in the Factory Service Manual. If you do not have one, I susgest you get one. Tradebit.com has them for about $10.

If the damage is deeper than allowable limits, then you will need a new cylinder. A good used cylinder is always a good option as well.
 

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Discussion Starter #3
Thanks, I am aware of the boring process and strength on a normal automotive engine. The limits are attached below. I can only find pistons .5mm or 1mm over which would be past the limit and I guess require sleeving. Jugs for this thing are more pricey (about $350+) way more then any 2 stroke i've worked on. would you still be able to use a STD piston as long as under that "limit" or someone know where I can get different oversized trust worthy pistons?
Thanks again
 

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Those limits in the book are for a stock bore. You can still bore that cylinder for a bigger piston.
Check the depth of the damage. If it's less than 0.5 or 1.0 mm, then get whatever piston works. If the depth of the damage is deeper than 1.0mm, only then will you need a new cylinder.

If you can do a re-bore, buy the piston first. Bring the piston and cylinder with you to the machine shop. Use the same piston to cylinder clearances as stock bore listed in the manual. I always print off this sheet and give it to the machinist.....He'll take care of the rest.
 

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Discussion Starter #5
Yeah upon further tear down it's going to need a lot more, cylinder is cracked, rod is twisted, bottom of piston completely demolished and inside the crank case
 

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That gives am indication that is was hydrolic locked at high rpm. It was definitely mal-used.

I hope your "friend" is footing the bill for this as he obviously caused this damage. It wasn't just from normal wear and tear.
 
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