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New here..Couple of questions.


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Just picked up a cherry 2005 YZ250 yesterday with what the owner says has about 50 hours on it..

He said hes done 2 sets of rings and thats it as far as the engine goes.

1.) should i do a piston/ring set just to be safe? $80ish seems alot cheaper than having it go boom..

2.) is there any reason to measure the cyl. ID? seems like jug A is only slightly smaller than Jug D..

3.) If i have jug B i should run piston B right?

4.) This is my first Yamaha.. Honda has gasket "sets" for a top end and bottom end, i looked around briefly at the microfiches and couldnt find a top end gasket set, is this something that needs to be pieced together individually? If there is a kit, does someone have the part number?

Thanks alot!!

-Brandon:ride:

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1.) should i do a piston/ring set just to be safe? $80ish seems alot cheaper than having it go boom..

Yes!

2.) is there any reason to measure the cyl. ID? seems like jug A is only slightly smaller than Jug D..

Just make sure its stock nikasil with no flaking and get a 66.4mm wiseco piston.

3.) If i have jug B i should run piston B right?

No, you should run a wiseco. There is no reason to run stock.

4.) This is my first Yamaha.. Honda has gasket "sets" for a top end and bottom end, i looked around briefly at the microfiches and couldnt find a top end gasket set, is this something that needs to be pieced together individually? If there is a kit, does someone have the part number?

The right piston kit will come with all the gaskets.

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I have a Wiseco now and am going back to a stock next month. Personal preference, I think.

To answer your question on the gasket kit, look up Cometic. The kit ($45 or so) has every gasket you will need to do a top end, and then some. It is really ingenius, and a shame that Yamaha doesn't offer a similiar kit. If you go to North County Yamaha on ebay, you can get a top end "kit" for around $130 and it has the important gaskets included.

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totally forgot about cometic... good point.

why are u switching back to stock if you mind?

its nice to finally own something that i can pretty much do anything in under 2 hours.

anyone know what size the tranny drain washer is?

the guy before me crushed the hell out of it so it weeps a little.

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gonna order the wiseco kit at work today.

dealer cost ftw ­čśĆ

Good! ­čśĆ Can anyone on here explain why someone would want the stock piston over wiseco? The forged piston is lighter, stronger, and pretty much lets you know when to rebuild it, while the cast piston holds all of its compression until one day it just blows. Its like a 2 stroke vs 4 stroke debate, the 2 stroke is obviously the better choice.

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Cast pistons have a higher silicon content. There for cast pistons are inherently more "slippery". Forged are harder on your cylinder. Cast pistons don't just blow. If you take care of your bike and change pistons every year at minimum a cast piston will be fine. In my mind a cast piston is higher performance.

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Cast is usually a heavier piston so you will get more torque (more linear power curve in most cases). But they also tend to crack skirts and even shatter if you're not careful. I've never had this problem though (ran a cast piston in my 125 for two years). It's cheaper as well. You can either match the piston to the cylinder to make yourself comfortable or just buy a D piston after the initial bike break-in. It shouldn't cause any problems.

Forged is lighter and can even prove to be a bit tough to handle if you go the single ring route (GOBS of ton end). Bottom end is about the same or maybe a tiny bit less (single ring has better bottom end as well). Forged costs more but will last longer if you're the type that doesn't like to dig into your motor very often. You HAVE to make sure to properly warm up your bike before riding it if you run forged though, otherwise you may cold seize your motor. If you dont cold seize it (seizures doesnt happen very often at all) you will increase wear on your cylinder. The reason why forged pistons don't come in 4 different sizes like the OEM pistons do is because they are made to tighter tolerances and expand at different rates.

So to sum it up. Both pistons are great for their application but you still have take care of your bike properly depending on the piston that you run.

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+1 on Rusky's explanantion. well said and well thought out. Answered a very common question with a definative and fact based answer backed up with proper disclaimer and all. Thats about the best answer for that question I have seen in a long time.

Bob

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The manual says to replace EVERYTHING. IMHO, just another way for them to make money. Unless someone has overtightened them and crushed the snot out of them somewhere in the past, they should be fine.

You only have to drill holes if the exhaust port has a divider/bridge in it. If I'm not mistaken, you shouldn't have one.

It will look like this is you have one. http://www.pilotodyssey.com/ExhaustBridgeRelief.htm

Edited by LemonDrizzle
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If you go by the book everytime you take a 10mm t-handle to your bike there's a washer or seal,nut,bolt,clip or gasket that "needs" to be replaced. I do replace somethings overtime but not all parts that the book requires. I have the Wiseco and i'm pretty sure I didn't drill any holes either.

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