Putting in new top end and reeds, opinions.

[Twostrokepower!!!]

Hello, i am going to replace the top end in my Kx85. I have already done alot of mods but i would like a new piston in it. Has approx. 70hrs on that piston(wiseco standard 48.5mm) I wanna look into options that are of a better durability and performance.
My choices are;
Vertex
Pro X
Wiseco
Oem
Out of all these which one will give me the longest life and engine performance? Also my cylinderr is brand new, do i neeed to increase from the standard bore? Or will it be fine as the same size?

And for the reeds, i am thinking of getting the boysen pro series reeds. They are supposedly the best... Any opinions on these parts for a nasty small bore 2stoker?

[arnego2]

With 70 hours on that little 85 cc piston Wiseco is your only option IMO.
I do 40 hours on my YZ250. 

[MetalMike1982]

I have to agree. Wiseco is the only brand out of the above mentioned that is forged instead of cast . From my understanding the forged is much more durable .

[cnrcpla]

I run wiseco in my 250, I know it isn't an 85, but they are pretty good pistons.

[scotty dog]

never had a wiseco fail, been using em for years

[Twostrokepower!!!]

Bike still runs perfect too, what about the oversize? do i  need another size? And any opinions on the reeds?

[arnego2]

Wiseco comes only in one size if STD, Woessner Pistons are forged too those come in 3 sizes. Not sure if they do pistons for the KX85 though.

Have a look http://wossneronline.com/forged_pistons/index.php?main_page=product_info&cPath=50_64_97&products_id=835

[Twostrokepower!!!]

There is 48.5 which is standard, and then 49.0mm, 49.50mm,50mm,and 50.50mm. Should i keep the stock bore or go alittle over because of the used cylinder?

[riffraff]

measure the bore in a few places, the manual should show you where to measure it, and decide from there.

[arnego2]

+1 any company putting in sleeves should be able to measure your bore.

[juliend]

There is 48.5 which is standard, and then 49.0mm, 49.50mm,50mm,and 50.50mm. Should i keep the stock bore or go alittle over because of the used cylinder?

You would not go to a larger size piston just because it's a used cylinder. If you do have to go up a size, you would do so because the cylinder is damaged and has to be bored and re-plated or sleeved. If the plating is in good condition, a stock cylinder is your best option. If the cylinder is out of spec, a simple strip and re-plate and again the STD piston would be the next option. If there is actual damage to the cylinder that requires welding or boring, then you would be looking for a larger piston.

Of course, this assumes the kx85 is plated? I believe it is.... 

[teampryor]

If you compete in motocross running a bored out mini is cheating in the 85 classes. Also ask anyone who has gone through the supermini phase of youth racing. Supers are high dollar, high maintenance, and are the hardest bike in the world to sell.
Keeping it stock also helps with resale.
You can strip and replate at stock bore size with better plating for around $200 but if you bore you can add a $100 to the price. Big bore pistons are more expensive too.
In small bore applications cast pistons work quite well cast pistons retain there size under heat better than forged pistons.
Wiseco makes forged pistons
Wossner makes forged pistons
Pro X makes cast and forged pistons
Vertex makes cast and forged pistons
OEM is cast.
I would reccomend the cast vertex piston. In motocross application by an aggressive rider ring at 10hrs and replace top end including wrist pin bearing at 20hrs. And yes get an Hour meter.
Thats our schedule on our yz 125s For trail riding play riding intervals are much longer.

[VintageBlueSmoke]

+1 to teampryor.

OEM pistons are more durable (last longer) than forged and are usually cheaper but don't usually have the wide range of sizes and performance improvements often required for modified cylinders and heads.

If you are not racing, don't bother with a bore unless the cylinger is damaged. If you are not racing, you'll probably out grow the bike and get on a 125 before you'll need (or afford) the miniscule addition of power.

If you are racing, check your rules very carefully. As stated, Supermini is a misnomer for the class. It should be called the SUPEREXPENSIVE class. I know guys that have over $10k in there Cobras! Just think how crazy they'll get on shifter bikes!

[ACMX]

I would go OEM. Wiseco is inconsistent.