I have recently had new rods made for my Aprilia engine via Reg and very nice they are too BUT they are each 200g heavier than the originals. This makes a huge difference to the balance of the engine which, in a narrow V4, is very difficult to calculate (I think there is something on the Lambda thread from Oz about the vector mathematics of this). I took the assembled engine (without the rings fitted but included with the engine for weighing) to Vibration Free who put it on their rig and balanced it. This entailed making a number of big holes in the flywheel and the addition of a substantial weight on the crank pulley. It took them some 40 hours (of which they only charged me 20!!!) but now they know what to do so in future it should be a lot easier for them. They said when they first put it on the rig and ran it up to 200 rpm it nearly jumped off so it would have been unusable if I had simply slung it together and bunged it in!