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questions about yz250f

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ok im looking at pistons and was wondering which one to go with. im leaning towards a vertex. i was also wondering what you guys thought about resleeveing cylinders. we have a really good machine shop where i live. I was also planing and trying to get my cases clean when i do this but dont really have an idea what to use to do it with was just wondering what some of you guys use and if it works good?

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Vertx, Wiseco, JE, and CP all make good pistons. Any one would be a good choice. There is really no need to sleeve your cylinder. you can replate your old cylinder or buy a new aftermarket cylinder for the same cost as installing a sleeve. A sleeved cylinder will also require special piston rings. The rings that are supplied with piston kits are not compatable with an Iron sleeve.

A plated cylinder is superior in every way to a sleeved cylinder. Sleeving really is only for cylinders that were originally equipped with a sleeve and an obsolete technology.

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I stick with OEM pistons of Motosport I don't wanna mess around with like after market ones but thats just me and they are a lot cheaper

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Contrary to what grimjim said above, the rings that are supplied with piston kits are compatible with a cast iron sleeve; however, they are not compatible with a chrome plated bore.

When it comes to plating vs sleeving, plating is a better option. Plating allows for heat to be more efficiently transferred between the cylinder and the cooling jackets when compared to sleeving.

And thats where my knowledge gets hazy...dont quote me on the following. I'm sure I asked the same question a while ago and was answered with a response that the plating was thinner than the cast iron and allowed heat to be transferred quicker because of less material and a higher thermal conductivity. The improved heat conduction allows for the engine to stay cool even when run lean or hot, and thus manufacturers were able to get more power out of it.

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Contrary to what grimjim said above, the rings that are supplied with piston kits are compatible with a cast iron sleeve; however, they are not compatible with a chrome plated bore.

When it comes to plating vs sleeving, plating is a better option. Plating allows for heat to be more efficiently transferred between the cylinder and the cooling jackets when compared to sleeving.

And thats where my knowledge gets hazy...dont quote me on the following. I'm sure I asked the same question a while ago and was answered with a response that the plating was thinner than the cast iron and allowed heat to be transferred quicker because of less material and a higher thermal conductivity. The improved heat conduction allows for the engine to stay cool even when run lean or hot, and thus manufacturers were able to get more power out of it.

Yes, correct. Rings and bores must be dis-similar materials. Chrome plated rings are fine in an iron bore.

The big advantage is the plated bore cylinder expands at the same rate as the piston. In an Iron bore cylinder, the bore expands at a different rate. the coefficient of expansion for Aluminum is about 10 times greater than for Iron. Plated bores are why you seldom see 'cold siezures' anymore. Because the rate of expansion on a plated cylinder closely matches the expansion rate for the piston, the clearance between the two remains more consistant and clearances can be reduced. This helps keep the rings square to the bore and provides better sealing.

Edited by 2grimjim

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Does anyone even chrome plate cylinders anymore? Maybe on a Harley, they like chrome on those things :smirk:

I'll echo what swede said and say go BIG bore it! Because more = better! The only thing better than cubic inches is cubic feet! No replacement for displacement!

Otherwise, you could just buy a new jug, or have yours replated at a place like Millenium Technologies or US Chrome (for nikasil, or "NiCom" plating). It will run you around $200 for a replate, pretty close to the price for a new cylinder... If you count the cost of a new piston assembly and a top end gasket kit, you're getting close to the price for a BB kit.

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