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Best Piston//oem Or Aftermarket?

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OEM seems to make tighter tolerance pistons, i.e. 4 different sizes to choose from according to factory stamp on cylinder. Wiseco offers one size fits all cylinders. :thumbsup:

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OEM seems to make tighter tolerance pistons, i.e. 4 different sizes to choose from according to factory stamp on cylinder. Wiseco offers one size fits all cylinders. :thumbsup:

I don't have anything against Wiseco (and have used them in the past) but now I use OEM Yamaha. As you mentioned a bit better tolerance range. They are a bit more expensive but I am OK with that.

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I was wondering the same thing. How do you tell what piston you buy with all the different sizes that Yamaha offers? I was :thumbsup: the last time I changed the piston and just went ahead and bought a Wiesco piston kit. I didn't see any difference in power but still have the old one to look at so I can compare when I do the next top end. I have two more races before I change it out.

I would like to stick to a Yamaha piston if I could figure out which one to order.

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I was wondering the same thing. How do you tell what piston you buy with all the different sizes that Yamaha offers? I was :thumbsup: the last time I changed the piston and just went ahead and bought a Wiesco piston kit. I didn't see any difference in power but still have the old one to look at so I can compare when I do the next top end. I have two more races before I change it out.

I would like to stick to a Yamaha piston if I could figure out which one to order.

A letter comes stamped on the cylinder (usually on the back, facing the carb). Match this letter up with the piston letter.

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I was wondering the same thing. How do you tell what piston you buy with all the different sizes that Yamaha offers? I was :thumbsup: the last time I changed the piston and just went ahead and bought a Wiesco piston kit. I didn't see any difference in power but still have the old one to look at so I can compare when I do the next top end. I have two more races before I change it out.

I would like to stick to a Yamaha piston if I could figure out which one to order.

As Motocross26 said, on the 250's its on the back side of the cylinder above the reed block. Should be pretty easy to spot.

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A letter comes stamped on the cylinder (usually on the back, facing the carb). Match this letter up with the piston letter.

This letter matching will apply more to a new bike than one that has some cylinder wear. As the cylinder wears you need to Measure your piston to cylinder wall clearance. This clearance can be tightened up by installing the apropriate size (larger) or letter piston. increments run in .01mm

A new bike may start out with a "A" cylinder and a "A" piston but after some wear will be a "A" cylinder with a "C" piston to gain the proper piston to wall clearance.

The "W" company hasn't found the OE cylinder sizes vary enough to warrant manufacturing A-D sizes.

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Pro-X do the A - D size for the yz. I have been running one for some time , seems to be as good as the OEM. Too bad I have a "D" barrel as there is no "E" size.

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Little know fact, The makers of the pro-x piston are also the the makers of most of the oem pistons for honda, yam, suzuki, and kawi.

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Little know fact, The makers of the pro-x piston are also the the makers of most of the oem pistons for honda, yam, suzuki, and kawi.

Thats true. It stands to reason that their A, B, C and D's are just stuff out of tolerance that they could not sell to the manufacturers.

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Little know fact, The makers of the pro-x piston are also the the makers of most of the oem pistons for honda, yam, suzuki, and kawi.

Once bought a Pro-X for a RM125 I owned and I was not happy with how much heavier it was compared to the stock piston. Also the crown height was slightly lower than the stock piston (not good). Needless to say that piston did not go into my engine.

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I just put in Athena piston not to long ago (10 hrs) everything good so far...can beat 35 bucks for a psiton/rings ect.. on ebay

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Thats true. It stands to reason that their A, B, C and D's are just stuff out of tolerance that they could not sell to the manufacturers.

That's a load of old cobblers RCannon. An irrational statement with no backup.

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Why???? The statement was more like a thought. No, I dont work fo rthe company. I have no interest in whatever piston a person wants to choose.

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NCY recommends (or at least recommended to me) always running the D piston for best power & sealing. I've installed a D piston twice now with no problems or issues.

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We buy Wiseco and ProX but be careful for the first minute when u warm up the bike with the wiseco because they heat up and extend very fast. :thumbsup:

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Wiseco pistons seem to wear the nickle coating faster then a OEM even if warmed up every run.
Cylinder wear is inevitable, no matter the piston type. I for one have found no evidence that Wisecos accelerate wear to the plating. And most of the wear on the plating comes from the rings, not the piston.

There is nothing wrong with using OEM cast pistons (and Pro-X falls in this catagory, as they are made by ART). In fact, they are the better choice for riders that won't take the time to do a proper break-in required by a forged piston, or warm the bike completely before riding.

For riders that will take the time to do a proper break-in, and will discipline themselves enough to fully warm their engines before each and every ride, Wiseco pistons are a superior product to OEM. They are more durable under high-heat high-load conditions, less prone to skirt breakage from piston slap if the bore has a bit too much wear on it, and longer wearing than any cast piston will ever be.

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