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Rebuild piston size 99 kx250

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What is the shop that will be doing the work telling you?

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And please tell me that your cylinder is sleeved and not plated.

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How do you tell witch is witch

Easy, a witch flies around on a broom at Halloween - sorry cohldnt help it.

You would be able to see the sleeve with the head off looking down into the barrel, kinda like looking at the rings of a tree trunk. A magnet would definitely stick to a sleeve. I am not 100% on this, but I dont think a magnet will stick to a plated cylinder.

If the shop doesnt know how much to bore a sleeved cylinder and is looking to you for that info, you need to find another shop. If that shop is going to bore a plated cylinder then you need to get your cylinder back and run away very fast.

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Idk the shop measured it

 

 

 

I haven't taken it to the shop yet but it is a plated cylinder I'm going to have it bored and plated

 

 

You are confusing me here.

 

Either send a piston in with your cylinder or buy one from the company you will be using and they will take care of it.

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Why bore it out?  Just replate to the stock size so you can use stock size pistons and rings.

 

I'd really be surprised if it was out of spec.  They're probably measuring it incorrectly.  You don't really need to measure anyway.  As long as the plating is intact and the crosshatching is present its fine.  If its worn enough to measure out of spec it'll be through the plating and quite obviously in need of repair.

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Keeping the stock bore size makes it much easier and cheaper to find replacement parts.  Boring and replating offers no advantage unless you bore it way out and increase displacement.  Installing a sleeve will require more labor including porting the sleeve which isn't always done very well.  The steel sleeve is also less resistant to wear than plating so you will have to send the cylinder off for a next oversize bore job with every rebuild.  Sleeved cylinders also tend to have problems with heat transfer which can result in piston seizure.

 

If the cylinder has damage such as cracks or deep gouging it can be welded and then plated.  Thats the way to go.

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Okay I took my cylinder into the shop. And they said it was nearly perfect and had no damage and that in should buy a standard size piston and leave the cylinder alone this said I now need to know what size piston to buy its eaither 66.40mm or 66.35mm and idk witch it is my piston and cylinder both are stamped B if that helps also it's a 99 kx250

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Just buy a stock size replacement piston.  The bore was 66.4mm on the KX250 for over ten years.  Any piston for a 93 to 99 kx250 will work.  Some time between 00 and 03 they lengthened the exhaust skirt, and I don't know if one of those will fit the earlier motors.

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