just wondering...

[tecatecrazy]

whats the difference btween an overbore and a bigbore if anything?---Joe 8)

[ATCRYDER]

Big Bores have seriously noticable Performance Gains, whereas overbores are minor to none. Big Bores also usally require case modification.

[TimSr]

Overbore is when you take a stock bore, and take a small mount off to make it square again, and to remove irregularities such as small scratches, and use a slightly oversize piston and rings. With most cylinders this can be done a few times, until its too thin to bore anymore. This is normally done as an answer to ordinary wear, or srcatches form a broken ring, or piston seizure or something like that. This is not a performance modification. When your cylinder hits maximum bore (minimum thinness) it must be resleeved, and you start over again. This is after about .080" on most. Resleeving can get pretty expensive, which is why do dont "bore to the max" but rather only bore what is necessary.

A big bore kit is when somebody removes the sleeve completely, and replaces it with a larger sleeve for the purpose of increasing displacement a substantial amount. This IS a performance modification and its expensive, and requires some type of aftermarket sleeve, as well as a piston and rings made for the big bore kit. This is how they get the 440EX 240 Blaster, 300R, etc. Overbore adds very little to the actual displacement.

[Wickedfinger]

There is no difference because the two really have nothing to do with each other. An overbore is exactly what it is - an over bore of the original cylinder diameter, usually in increments of hundreths of an inch. A Bigbore refers to the larger displacement class of motors. Think in terms of muscle cars - Big Blocks v's Small Blocks. Back in the day, with ATV's, it pretty much meant anything over 350cc's - but today anything called a Bigbore would need to be at least 500+ cc's or greater. You really have three different classes of 4 stroke ( fullsize) motors now - 150 - 300cc's would be considered smallbore, anything 300 - 500cc's are mid-class size motors, and your 500+cc's are big bores. AT least this is the way I look at it.

[skippy]

nice through complete response tim sr! you said it all!