C.C. gain when boring question.

[rusty rocket]

Im having a mechanic friend do some work on my motor while the frame is getting powder coated. At first I thought it was hard valve seals because the bike sat for many years and it smoked a bunch. My friend called and said he had bad news, you have a scored piston but I should be able to hone it and put a new set of standard pistons. Yesterday he called and said there were pits in the jug that are going to take 50 thousandths to get out. So long story longer what will the c.c.s be when it gets new 50 thousandths over pistons? Or is it so small it doest add much?

 

[fredintoon]

Hi Rusty,
it ain't much.
2 x (2PiR - 2Pir) Gives the increase in piston area.
That x stroke gives the increase in engine capacity.
Grab your math box and go!

 

[jay760]

Problem you have is xs pistons go up in 0.25mm not thousandths, think they advertise 1mm over as 670 or 680cc can't remember which

 

[5twins]

Plug the numbers in and let us know. Stock bore is 75mm and stock stroke is 74mm .....

http://www.nightrider.com/biketech/calc_displacement.htm

 

[chizler62]

Number of cylinders X 3.14 X (Bore-cm/2)^2 X Stroke-cm = displacement

example......... 2 X 3.14 X (7.525cm/2)^2 X 7.4cm = 657.88

 

[rusty rocket]

jay760 you are correct. it would be the .50mm over. going to get pistons thru 650 central.

 

[chizler62]

2x3.2014x (7.55/2)^2x7.4=662.26

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[hard_y_rd]

jay760 you are correct. it would be the .50mm over. going to get pistons thru 650 central.

1st size over is .25 over

 

[TwoManyXS1Bs]

For our 2-cylinder XS650 engines, with the standard 74mm stroke, you can simply use the bore (in millimeters) squared, times the constant of 0.116239 to find the displacement.

(Bore) x (Bore) x 0.116239 = Displacement in CC's

75 x 75 x 0.116239 = 653.84 cc

Bore => Displacement
75.00 => 653.8 cc (STD bore)
75.25 => 658.2 cc (1st over)
75.50 => 662.6 cc (2nd over)
75.75 => 667.0 cc (3rd over)
76.00 => 671.4 cc (4th over)
76.50 => 680.3 cc (6th over)
77.00 => 689.2 cc
78.00 => 707.2 cc
80.00 => 743.9 cc (750 kit)
80.25 => 748.6 cc
83.00 => 800.8 cc (Crazy big)

 

[chizler62]

For our 2-cylinder XS650 engines, with the standard 74mm stroke, you can simply use the bore (in millimeters) squared, times the constant of 0.116239 to find the displacement.

(Bore) x (Bore) x 0.116239 = Displacement in CC's

LOL I couldn't remember that constant off the top of my head.
long way still gets you there!

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[rusty rocket]

Kool, thanks guys. So it looks like im going to have a xs 662.