What is the difference between over bore and big bore?

 

bigbore is a term for making the cylinder larger around for more overall power. for instance a z400 turned into a 450.
overbore is lets say you blow up your top end, scratch up the inside of your cylinder, you bore it out very small amounts (.020, .040 ect) to fix the scratch, not for more power.

 

Big bore is also the term used for the larger sized available engines. Nowadays all the 800's, 700's and 650's are considered big bores. A few years ago, a 400 was 'big bore'.

Jaybee

 

So if I bore my cylinder .80 over is that a big bore or an over bore?

 

that would be considered big bore. over bore is in 3 decimals, like .080, .80 is almost 1 mm.

 

A big bore requires a welder. [img]i/expressions/face-icon-small-happy.gif[/img]

No, really, .080" over is just over 2 millimeters. That is considered a big bore to some. In fact I think the Raptors big bore is 2mm.

 

any machine work done to a stock sleeve and cylinder without altering anything but the actual bore is just an over bore. big bore would mean you change your bore to the extent you need additional work done to reinforce your cylinder and possibly even a bigger jug for cooling purposes. that's why people purchase big bore kits because they come with already reinforced cylinders and what not. there are what people will refer to as big bore engines which are just that, an engine with a large stock bore, but that's talkin like big block small block with cars. you can have a small block engine with a big bore and long stroke that may equal the same cubic inches as a big block, however, it's still a small block just with a big bore and in some cases a longer stroke. you can have any size engine though with a big bore. hope that all makes sense.

 

Terminology eh....LOL
IMO, over bore is when the stock sleeve is bored. ie: my 250R with the stock cylinder bored a cpl times.
Big bore is when a aftermarket sleeve or cylinder is used. ie: my 250R with my 310 cylinder on it.

.80 over (2mm) is an overbore. [img]i/expressions/face-icon-small-smile.gif[/img]