Re: OMC Big Twin Cylinder Bores

[Mumbles]

While measuring the bore, turn your bore gauge 90 degrees and measure at both top and bottom of the cylinder where the rings travel. The rings, not the pistons, are what wears the bore and comparing the measurements at 90 degrees to each other will tell you how much the cylinder is out of round plus give you the amount of taper. New rings in a used cylinder must be fitted at the tightest place, which is usually at the bottom of their travel. It is generally agreed that you can use +0.010 oversize rings in a given bore if fitted properly. In other words, you can use +0.030 OS rings in a cylinder which has been bored 0.020 OS. It might take a bit longer for them to seat in but it can be done.