As Vince says, welding up the pin and offset grinding is one choice. Just offset grinding could give us a 4mm~4.5mm stroke, but we'd be compromising strength by going down to a 22mm big end pin. Not a total disaster as this give us a good selection of MX rods to choose from, but whether they're up to handling the extra mojo is of course open to debate. Why did Honda see fit to use 25mm pin if a 22mm would have done the job.

Reducing the hole in the mating crankwheel is not too tricky. My mate has stroked many singles by welding and offset boring the big end pin hole. He makes a good job of it and has won many races.

So many things to do.....