I have an extra cylinder I want to send out for boring.  Are the bores supposed to be the same size at the recommended measure point of the skirt as
near the top ring?  I will be using a stock material type Yamaha piston. The book says 0.040-0.045mm clearance from most narrow part of cylinder to widest part of piston if I'm not mistaken.  W

After reading his name in a positive light on this forum a few times, I called Bill Bune Enterprises and he seemed receptive to do the work,
but told me to include the clearances I wanted.

I'm thinking same bore all the way down w/recommended Yamaha clearances.       

What do you think?  Any bad experiences with boring? 



 

  

 

Can't go wrong with BB.

shoot for book specs 40-50 microns 10 mm above skirt bottom perpendicular to pin axis

problem is how much is needed to bore?
They will bore/hone to the size that will clean-up

Don't overthink.  Bill Bune has been around for decades and knows what they are doing.  Yamaha dealers send them work.  They know where to measure the piston skirt and how to machine so that you end up with basically a "factory new" bore that's a little oversized to clean up the wear and imperfections.

Just tell them you want to use the Factory Yamaha piston clearance specifications and they will do the rest.  If they don't have the factory clearance spec, give them the specs from the manual and be sure to clearly state if they are in mm or inches.  

Ok, so, "Factory Yamaha piston clearance specifications and 0.040-0.045 MILLIMETERS clearance". Roger.

You might want to consider sending them just the cylinder and asking them what oversize will be required to clean up the damage. Then buy and send them the recommended oversize. Takes longer but you would be sure you have a like new assembly without buying multiple oversize pistons. (unless you are 100% sure what size will fix the damage)