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Need Some Top End Advise

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     I plan on doing a top end job on my 05 yz250 with the wiseco piston kit. It is not blown up or anything but I bought it used and I'm pretty damn sure its the stock piston lol. Y'all tell me what I need to know in order to get his done correctly because I have never done this and I don't plan on screwing it up. Any advise helps, thanks. 

p.s. what does it mean to measure the clearance? and how do you do it?

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I was in the same boat. I bought a standard wiseco piston from RMATV, and sent the piston along with the cylinder to powerseal to have it matched. 

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Alright and what do you do with that once you have the numbers?

 

I have several piston kits in my box, so I can use them. Last year I got a brand new cylinder and had to use a "D" Size OEM piston to get the piston clearance between 0.045 - 0.05 to 0.1mm

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sand paper is a bad idea, 

 

use a scotch brite scuffing pad (red one) from a autobody section at the store. And wd40, you are trying to clean out the honing grooves, not sand them down.  Rinse with hot water/dishsoap  than assemble.

 

If the piston is stock and its 2005, order a slight oversize piston

 

wossner (forged)

oem (cast)

pro x (cast)

 

all make slight oversizes.  The wiseco is a one size only, and by now with the bore wear on a bike that is 8yrs old, it would be a sloppy fit.

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Ok thanks guys, idk if it matters or not but I heard forged is better than oem that's why I thought about getting a wiseco, which piston would best suite an 8 year old bike? Possibly just the D size oem?

lots if people dislike Wiesco but at my shop I run Wiesco in ever bike I rebuild unless there on budget then I go to cheaper stuff

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lots if people dislike Wiesco but at my shop I run Wiesco in ever bike I rebuild unless there on budget then I go to cheaper stuff

Alright, how do you think the wiseco will fit in an 8 year old bike? Will it be a sloppy fit like what adam8781 said? And if it is a sloppy fit, what will happen? 

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This is a link to yamaha-australia's main site. They have PDF versions of the service manual for all 1900's and newer yamaha motorcycles. Look up your bike, download the service manual and then go to the "topend". You will find everything you would ever need to know about doing the rebuild.

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Just order a wossner forged piston, the biggest one or size D. its the same price as the wiseco give or take a few bux

Too small a piston will rock back and fourth in the cylinder bore egging out the cylinder abd wearing out the piston very quickly. With a cast that means shatterd piston skirt and a big pricey rebuild. With a loose forged it just wears out the cylinder quickly

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The OEM ''D'' sized piston is the same size as all the aftermarket pistons. After you have run one piston through the stock cylinder it will need the D sized or stock sized Pro-x, wiseco, woessner piston. The reason you want to measure the cylinder bore is to make sure it doesnt need to be replated. 

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Take your cylinder to a local machine shop and have them check out the bore if you are not sure.  Most shops only charge $20 to hone the cylinder if it needs to be cleaned up.  They will also check size and let you know what size piston to order and make sure your plating is still in good shape.  Most shops can also get pretty good deals on most top end kits if you want to get it from them.  Good luck. 

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Ok so if I were to check the clearance with feeler gauges, would I then take half of the measurement of which feeler gauge I used since it is only measuring one side?

You cant measure actual distance between the piston and cylinder with a feeler gauge, that would F-up your cylinder and probably not give you an accurate reading. The only way to measure your clearance is measure the cylinder diameter with a cylinder bore gauge. Then measure your new piston diameter with a dial caliper. Your clearance is found by subtracting your piston diameter from your cylinder diameter.

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Surely not as accurate as using a cylinder bore gauge and a dial caliber but it won't F-up your cylinder neither IMO. I use feeler gauges and with its rings in place you get a better reading than having just to take a guess. Would be nice to see how much difference in accuracy there is between bore gauge and dial caliper vs feeler gauges :)

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