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
IT sounds like you're looking at YPVS/Banshee pistons, which need a reed valve.
You want piston port pistons.
Not sure if you will find any 64.25mm cast pistons so you may need to run Wossner or Wiseco forged pistons.
There are some .25 oem Yamaha pistons on Ebay
And forged are available from Economy Wossner R5 pistons (https://www.economycycle.com/shop/yamaha-rd250350400r5ds6ds7-parts/engine-related/pistons-yamaha-rd250350400r5ds6ds7-parts/wossner-piston-kits-yamaha-r5-all-years-sold-each/)
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.
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. :twocents:
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. :twocents:
measure once, buy once.
Quote from: m in sc on December 07, 2022, 10:42:53 AM
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. :twocents:
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.