Hi, I have had a full engine rebuild on my 1200cc sporty, I have had the cylinders rebored and had a 1.0 oversize on the piston. Can someone please tell me what cc the bike will be now,and is there a simple method to work this figure out. Thanks in advance, I know someone here will have an answer.

Think this may be close (?) I believe your factory stock bore is 88.8mm with a stroke of 96.8mm. Your bore was increased by 1mm so you now have a bore of 89.8mm with a stroke of 96.8 The volume of each cylinder is [3.14159 X Radius squared] X height. I don't have a calculator handy so I will let you work out the details.

To get the most accurate answer,you NEED to know your bore size.And obviously,yours is now slightly larger than stock. Basically the formula isi x radius squared x your stroke(this gives the SWEPT volume of EACH cylinder)x the number of cylinders in your motor. Let's have an example:my Triumph Daytona has a capacity of 955cc and is a 3 cylinder motor with a Bore of 79mm and a Stroke of 65mm.So ,with my trusty and oh-so-necessary calculator i work it out like this: Pi(3.142) x radius squared(radius of 79mm bore is 39.5mm; so 39.5 x 39.5) x stroke(65mm). This gives the volume of EACH cylinder;then x 3 for total motor capacity. 3.142 x 39.5(squared) x 65 =3.142 x 1,560.25 x 65 =318.649.85cc per cylinder.3 X 318.649 = 955.947cc Substitute your Harley bore and stroke and number of cylinders and Voila! Can't help with your exact capacity,but that's how you do it. Numbers are so magical.

Thanks for all the usefull and helful imformation, I just need to sit down and get my head round it. Does anyone know how big you can go on a sporty without having to think about a stronger crank.

If your bike is the bike as your avatar shows,,,, Just go to Scream'n Eagle catalog to look for New barrels and piston sizes that will fit yours and that will tell you a lot.. signed....BUBBIE OOOOPsy ,,I reread and you have a 1200 sporty,,,, ??? go look anyway ????1250 CC??