Piston ace 100

[mycall]

I need to have my cylinder bored. Right now it has a .02 over piston in it but it's quite abit out of tolerance. I messurred it with a Sterrett inside mic and it messurred 50.57 mm at the top and 51.04 at the very bottom of the sleeve. Can I go .04 over or should I go .05?

[---]

That's a close call. Assuming the skirt is now 51.04mm, that is right at about 0.040" over. That doesn't leave any wiggle room, and it might depend on the actual dimension of the piston chosen, since they rarely run true. A machinist generally bores a cylinder to match a given piston for that reason, but it almost demands that you have the piston first. If you can't insert the skirt of a 0.040" over piston into the skirt of the cylinder as it is now, you could probably bore it 0.040" over. If it fits correctly, it probably won't work just because there is nowhere to go for the machinist at the bottom of your cylinder.

I am going to guess that it is too close to call without the oversize piston in hand, and that pretty much suggests the next size up just to be sure.

[mycall]

Thanks. If it did'nt quite clean up at the very bottom would that be a problem?

[---]

Not for me, but you have to work with the machinist. Unless you have a boring bar setup of your own. Then you can do what you are comfortable with.

Perhaps you could write to either Paul or Bruce and ask if they have a piston in stock that they could mic for you, so you have a feel for whether you can get by without going to a larger than 0.040" over piston. I know Paul is busy this weekend with MX at a track in NY, but you can always ask.