Top End Rebuild Help

[R5HiFive]

Hi,

First off, thanks for taking the time to read this! 
Straight to the point, and backstory after;

I need new pistons for my R5 top end rebuild & I have a few questions. 
1) In regards to pistons, which piston would be best for a simple straight out of the box rebuild with a 64.25mm oversized bore?  I ask this because I've seen forums of people mentioning filing and grinding down piston skirts/ports for cast vs forged pistons and my head is spinning! I just want a piston that'll work out of the box with a simple R5 cylinder jug rebore to 64.25mm.  Is this possible?

2) Forged pistons, Wiseco, I like the sound of them - are they fitting for a street bike, every day rider?  The price is no issue.  I want something reliable and forgiving. 

Thanks again!
Finally, after much creativity and heat and time and leverage and heat and elbow grease, I managed to get the original cylinder jugs off the motorcycle.  Over 50 years of crud on this crank studs! A local machine shop in town helped me.  Jacking power off the crank to exhaust port with rounded off hardware against the exhaust gasket - this is the way folks.
Before beginning with this rebuild, I purchased and got running again this motorcycle and managed to put 50 miles on it.  I could tell the rings were worn out pretty bad so here we are.  New top end! First time for everything

I appreciate the help.

-Thomas

[bitzz]

IT sounds like you're looking at YPVS/Banshee pistons, which need a reed valve.
You want piston port  pistons.

[rodneya]

Not sure if you will find any 64.25mm cast pistons so you may need to run Wossner or Wiseco forged pistons.

[1976RD400C]

There are some .25 oem Yamaha pistons on Ebay

[SoCal250]

And forged are available from Economy   Wossner R5 pistons

A little general info to answer some of your other questions:
- OEM Yamaha pistons are cast, as are Pro-X, TKRJ, Vertex, Mitaka, etc.
- Wossner & Wiseco are forged. Forged pistons require a little larger clearance than cast. (Follow manufacturer specs for required clearance.)
- As mentioned above by bitzz, your R5 is a piston port engine, while the RD models utilize a reed valve on the intake tract. As a result, R5 pistons do not have the windows in the piston skirt.
- See attached for skirt tang trimming. With R5 pistons you will not have to deal with this.

[dgorms]

Some bores won't clean up entirely at .25 you might want to consider .50. Have a competent machinist measure and evaluate the cylinders and proceed from there. Always acquire new pistons prior to boring.

[m in sc]

get your guy to measure the cyls 1st, then order what he recommends. I got bit by this 1 time, and sat on some 1.0mm over pistons for a while because it tapered enough where i needed to go 1.25 over on a set. 

measure once, buy once. 

[Striker1423]

get your guy to measure the cyls 1st, then order what he recommends. I got bit by this 1 time, and sat on some 1.0mm over pistons for a while because it tapered enough where i needed to go 1.25 over on a set. 

measure once, buy once.

^This.

The pain of waiting to ship and have your cylinders inspected might suck, but it's better to be sure than not.