The International CBX Owners Association

Hi all, getting prepared to call the machine shop that did my boring for the 2nd over pistons on Monday.
It said on the box that they were 65mm, my boring measures 65mm but my ring gap is .014, factory specs is .006 to .012 now I measured my piston skirts and they are .2mm or .007 smaller that the bore.

What is the 65mm is piston size ? how to determine proper boring measurement, do you measure the piston skirt and add .002 for the clearance needed. I'd like to have answers on how is determined to arrive to proper boring size, what should the pistons themselve measure being 2nd oversize, could I have defective pistons sizes.
Thanks for the help.
Marc

This may help Marc....

http://wiseco.com/PDFs/Manuals/RingEndGap.pdf

Piston size is measured at the skirt ( a little way up,) normally across the thrust faces ( front to back) on used pistons....

Give the pistons & block to a reputable motorcycle machine shop, used to air cooled motors & they should do all the calculations ( hence the risk) for you....

However, Just to make sure, call Wiseco to get the correct info, as different piston manufacturers/types have different requirements....

Maybe I am looking at this all wrong, but....
Let's start with the stock bore of 64mm. Honda specified the oversized steps as 1st 0.25mm, 2nd 0.0mm, 3rd 0.75mm and 4th 1.0mm.
Shouldn't a 2nd over then be 64.5mm and not 65mm???

Let's start with the stock bore of 64.5mm-----------wake up Mike

Oh, well What's half a milimeter among friends In my mind, I am still in the Conch Republic.......

Quite a change from The Bull and Whistle to all that snow removal equip in Ohio, isn't it? Did you make it to 7 fish?

Hi again, I called the machine shop today explaining my clearance issues with the piston to wall and ring end gap at .015

They tell me that if the manufacture produces 65mm like my 2nd over it's up to them to calculate the clearance within the pistons to wall. So if you buy 65mm that's the hole size you get, the pistons are what determines the clearance. If I am deviating from Manufacture specs, where do you take reference to measure piston to wall, I replied .040 above the bottom of the skirt, just as the manual indicates.

Not impressed, even though I brought them specs from forums to have piston to wall at .015 to .002, I am now going to look for another machine shop. These sleeves can serve bigger pistons at a later time.

This project is on hold, thanks to everyone that listened and contributed, much appreciated.

Marc

Thanks for the feedback Marc, I would have asked them to what tolerance they bore ? That's by the by hope you get better luck in your new project.
However, It would be good ( for the benefit of the forum) to name the shop & possibly prevent the same happening to another member who may be local...

cbxtacy wrote:Quite a change from The Bull and Whistle to all that snow removal equip in Ohio, isn't it? Did you make it to 7 fish?

No, George, we skipped Seven Fish this time. We didn't really eat that much. Only nice dinner we had was at the Grand Cafe and that consisted of three appetizers split between the two of us.

Defintely, the best advice is to talk with Wiseco. Among other things to put into the equation is what type pistons are they: cast or forged? Forged pistons are fit looser than cast. Wiseco will be able to give you, or your machinist, the proper clearance to cut.